A novel hydrazone-based fluorescent "off-on-off" probe for relay sensing of Ga3+ and PPi ions.

A novel hydrazone-based fluorescent probe (E)-3-((2-(benzo[d]thiazol-2-yl)hydrazono)methyl)-4H-chromen-4-one (BTC) has been rationally designed and synthesized. BTC can subsequently detect Ga3+ and PPi ions through the absorption and emission off-on-off response with high specificity. Importantly, fluorescent probe BTC can well discriminate Ga3+ from Al3+ and In3+. The association constant (K) was calculated as 2.06 × 104M-1, and the limit of detection (LOD) was calculated as 4.88 × 10-2µM. Competitive binding studies also illustrated good results of the probe BTC towards Ga3+. Job's plot and HRMS results substantiated the 1:1 stoichiometry between BTC and Ga3+ ion. The interaction binding mode of BTC with Ga3+ was proposed by HRMS, 1H NMR spectral titration, UV-vis absorption and fluorescence spectral measurements. The combination of the restraint of the photo-induced electron transfer (PET) process and the chelation enhanced fluorescence (CHEF) process is responsible for the fluorescence enhancement of this probe. The in situ chelated BTC-Ga3+ could further monitor pyrophosphate ion (PPi) by demetallization process with quenching fluorescence emission. Additionally, the BTC and BTC-Ga3+ showed good cell permeability and could detect Ga3+ and PPi ions in onioninner epidermal cells, respectively.

Fenton-like reaction of the iron(II)-histidine complex generates hydroxyl radicals: implications for oxidative stress and Alzheimer's disease.

The hydroxyl radical (˙OH), generated from Fenton/Fenton-like reactions of iron(II) species in biology, can oxidatively damage biomolecules, inducing oxidative stress and diseases. However, this common understanding has been questioned recently after a carbonate radical was observed from the Fenton-like reaction of the iron(II)-carbonate complex. Herein, we report that the Fenton-like reaction of the iron(II)-histidine complex, one major iron(II) species in blood plasma, can occur at neutral pH to generate ˙OH, not iron(IV). Our findings and critical analyses on relevant studies clarify the above doubt, reveal a new pathway of causing oxidative stress by the iron(II) species, and have implications for Alzheimer's disease.

A hydrazone-based spectroscopic off-on probe for sensing of basic arginine and lysine.

A simple probe BHN based on naphthol and benzothiazole is reported for detecting of arginine (Arg) and lysine (Lys) with high selectivity and sensitivity. The BHN in aqueous solution upon reacting with Arg or Lys induced a visible color change from colorless to yellow. The probe BHN can also be employed for fluorescence turn-on sensing of Arg and Lys with the limits of detection (LOD) of 5.20 × 10-2 µM and 3.69 × 10-2 µM, respectively. The naked eye colorimetric and fluorimetric detecting is lack of sensitive to other common amino acids including Gly, Ala, Ser, Pro, Val, Thr, Cys, Leu, Ile, Asn, Asp, Glu, Gln, Met, His, and Phe. The sensing mechanism has been proposed by pH investigation and 1H NMR spectra.

Selective sensing of PPi by fluorogenic Al(III)-probe complex in aqueous medium.

A newly designed Schiff base probe JN has been synthesized. It is highly selective and sensitive towards Al3+ in nearly 100% aqueous medium by exhibiting a dramatic "turn-on" fluorescence response at 495 nm (λex = 450 nm). The sensing mechanism of JN towards Al3+ ions was proposed as the combination of PET, ICT, ESIPT, and CHEF processes according to spectra studies and theory calculations. The in situ generated mononuclear Al(III) complex JN-Al3+ could sequentially detect PPi ions by turn-off fluorescence response. The selectivity and sensitivity of the JN-Al3+ complex towards PPi ions are based on demetalization process. Interestingly, the fact that Al3+ can bind with 1, 2, or 3 PPi has been revealed by HRMS study. The probes JN and JN-Al3+ complexes were able to capture Al3+ and PPi ions, respectively, as demonstrated by fluorescence imaging of the adult zebrafish and onion inner epidermal cells samples.

Selective monitoring ATP using a fluorogenic Al(III)-probe complex in aqueous medium.

A simple commercially available probe 8-hydroxyjulolidine-9-aldehyde (HJ) has been developed as a turn-on fluorescent probe specifically for Al3+ and characterized systemically. The probe HJ for Al3+ ion exhibits strong green fluorescence under ultraviolet light. The HJ acted as an OFF-ON-OFF type fluorescent probe for Al3+ and ATP in nearly 100% aqueous media. The 1:1 binding stoichiometry between probe and Al3+ has been established from Job's plot and HRMS studies. The limit of detection for Al3+ ion is found to be 5.75 × 10-8 M. The large association constant between HJ and Al3+ ion is 1.05 × 105 M-1. Detailed insights of probe-metal interaction mechanisms have been studied by the density functional theory (DFT) as well as the time dependent-DFT (TDDFT) calculations. Moreover, benefiting from the water solubility and biocompatibility of the probe HJ and its HJ-Al3+ complex, they have also been successfully applied to detect Al3+ and ATP by bioimaging in onion epidermal cells and adult zebrafish respectively.

Detection and identification of the oxidizing species generated from the physiologically important Fenton-like reaction of iron(II)-citrate with hydrogen peroxide.

The Fenton-like reaction of iron(II)-citrate with hydrogen peroxide is physiologically important because it is associated with the oxidative stress and pathological processes induced by the redox-active iron pool in vivo. However, the oxidizing species generated from this reaction at neutral pH has not been convincingly identified because two extremely unstable and hard-to-differentiate species, the hydroxyl radical (•OH) and iron(IV) (ferryl) species, can be produced. Identifying this species is essential for understanding the reaction mechanism. Although there were few data that reported the detection of •OH from this reaction by using the EPR and fluorescence techniques, most of these data were obtained without the necessary assessment with a •OH scavenger. Furthermore, these two techniques may not be able to differentiate the •OH and iron(IV) species. Thus, these reported data cannot lead to a convincing conclusion that the •OH, not the iron(IV) species, was generated. Therefore, in the study reported herein, we carried out systematic investigations first by using the EPR and fluorescence techniques combined with a •OH scavenger to detect the oxidizing species generated from this Fenton-like reaction. Then we utilized NMR spectroscopy and for the first time obtained convincing evidence to demonstrate that this oxidizing species is the •OH rather than iron(IV) species. We also determined the second-order rate constant of the reaction, 3.6 × 103 M-1s-1 (pH7.0, 25 °C), by using the stopped-flow spectrophotometry. On the basis of these findings, a scheme is proposed for the mechanism of this physiologically important Fenton-like reaction.

Monitoring ADP and ATP in vivo using a fluorescent Ga(iii)-probe complex.

A naphthol-based sensor (L) was designed and synthesized for the specific recognition of Ga3+ using fluorescence enhancement. An in situ generated L-Ga3+ ensemble detected ADP and ATP more selectively through a fluorescence "switch off" response, which was confirmed both in cells and in adult zebrafish.

Synthesis of a Novel Fluorescent Ruthenium Complex with an Appended Ac4GlcNAc Moiety by Click Reaction.

The O-linked ß-N-acetylglucosamine (O-GlcNAc) modification is an abundant post-translational modification in eukaryotic cells, which plays a fundamental role in the activity of many cells and is associated with pathologies like type II diabetes, Alzheimer's disease or some cancers. However, the precise connexion between O-GlcNAc-modified proteins and their function in cells is largely undefined for most cases. Confocal microscopy is a powerful and effective tool for in-cell elucidation of the function of biological molecules. Chemical labeling of non-ultraviolet or non-fluorescent carbohydrates with fluorescent tag is an essential step that makes intra-cellular microscopic inspection possible. Here we report a strategy based on the 1,3-dipolar cycloaddition, called click chemistry, between unnatural N-acetylglucosamine (GlcNAc) analogues Ac4GlcNAc (substituted with an azido group) and the corresponding fluorescent tag Ru(bpy)2(Phen-alkyne)Cl2 (4) to synthesize the fluorescent dye Ru(bpy)2(Phen-Ac4GlcNAc)Cl2 (5) under mild and neutral reaction conditions. Moreover, 5 showed good stability, desirable fluorescence characteristics, and exhibited rather low levels of cytotoxicity against sensitive MCF-7 cells. Additionally, we have achieved successful fluorescent imaging of 5 transported in living MCF-7 cells. Cell images displayed that proteins are potentially labelled with 5 in the cytoplasm.

Constraining the conformation of peptides with Au nanorods to construct multifunctional therapeutic agents with targeting, imaging, and photothermal abilities.

We demonstrated an easy-to-use strategy, instead of the tedious cyclization of the peptide backbone, to constrain the freedom of an RGD (arginine, glycine, aspartic acid) sequence with gold nanorods. We further constructed a multifunctional therapeutic agent which showed targeting, application in two-photon photoluminescence imaging, and near-infrared photothermal ability, suggesting the potential of this novel strategy in the development of RGD-containing drugs for biomedical applications.

Shelf-life extension of semi-dried buckwheat noodles by the combination of aqueous ozone treatment and modified atmosphere packaging.

The present study investigated the combined effects of aqueous ozone treatment and modified atmosphere packaging (MAP) on prolonging the shelf-life of semi-dried buckwheat noodles [SBWN; moisture content (22.5±0.5%)] at 25°C. Firstly, the different concentrations of ozonated water were used to make SBWN. Subsequently, SBWN prepared with ozonated water were packaged under six different conditions and stored for 11days. Changes in microbial, chemical-physical, textural properties and sensorial qualities of SWBN were monitored during storage. Microbiological results indicated that adopting 2.21mg/L of ozonated water resulted in a 1.8 log10 CFU/g reduction of the initial microbial loads in SBWN. In addition, MAP suppressed the microbial growth with a concomitant reduction in the rates of acidification and quality deteriorations of SBWN. Finally, the shelf-life of sample packed under N2:CO2=30:70 was extended to 9days, meanwhile textural and sensorial characteristics were maintained during the whole storage period.