Bin Liu

Naphthol-based fluorescent sensors for aluminium ion and application to bioimaging

Three naphthol Schiff base-type fluorescent sensors, 1,3-Bis(2-hydroxy-1-naphthylideneamino)propane (L1), 1,3-Bis(1-naphthylideneamino)-2-hydroxypropane (L2) and 1,3-Bis(2-hydroxy-1-naphthylideneamino)-2-hydroxypropane (L3), have been synthesized. Their recognition abilities for Al(3+) are studied by fluorescence spectra. Coordination with Al(3+) inhibited the CN isomerization of Schiff base which intensely increase the fluorescence of L1-L3. Possessing a suitable space coordination structure, L3 is a best selective probe for Al(3+) over other metal ions in MeOH-HEPES buffer (3/7, V/V, pH=6.6, 25°C, λem=435nm). A turn-on ratio over 140-fold is triggered with the addition of 1.0 equiv. Al(3+) to L3. The binding constant Ka of L3-Al(3+) is found to be 1.01×10(6.5)M(-1) in a 1:1 complex mode. The detection limit for Al(3+) is 0.05μM. Theoretical calculations have also been included in support of the configuration of the L3-Al(3+) complex. Importantly, the probe L3 has been successfully used for fluorescence imaging in colon cancer SW480 cells.

Probing chromium(III) from chromium(VI) in cells by a fluorescent sensor

Cellular uptake of Cr(VI), followed by its reduction to Cr(III) with the formation of kinetically inert Cr(III) complexes, is a complex process. To better understand its physiological and pathological functions, efficient methods for the monitoring of Cr(VI) are desired. In this paper a selective fluorescent probe L, rhodamine hydrazide bearing a benzo[b]furan-2-carboxaldehyde group, was demonstrated as a red chemosensor for Cr(III) at about 586 nm. This probe has been used to probe Cr(III) which is reduced from Cr(VI) by reductants such as glutathione (GSH), vitamin C, cysteine (Cys), H2O2 and Dithiothreitol (DTT) by fluorescence spectra. Cr(VI) metabolism in vivo is primarily driven by Vc and GSH. Vc could reduce CrO4(2-) to Cr(III) in a faster rate than GSH. The indirectly detection limit for Cr(VI) by L+GSH system was determined to be 0.06 μM at pH=6.2. Moreover, the confocal microscopy image experiments indicated that Cr(VI) can be reduced to Cr(III) inside cells rapidly and the resulted Cr(III) can be captured and imaged timely by L.

Application of nanodiamonds in Cu(II)-based rhodamine B probes for NO detection and cell imaging

Nitric oxide functions as an important signalling molecule in many biological systems. Nanodiamonds (NDs) have attracted enormous attention in the field of biomaterial science for biosensing applications and drug/gene delivery. In this work, one novel Cu(ii)-based rhodamine B probe for NO detection was composed which was covalently bound to the nanodiamond (ND) surface. The results showed that the covalently conjugated ND probe could detect Cu2+ and NO sequentially with high sensitivity, high stability and good reusability compared to a free rhodamine B probe in CH3CN/HEPES (pH 6.8, v/v, 1 : 1). The detection limit for NO was estimated to be 10.5 nM. In addition, the response to NO was reversible in the presence of O3, which has attracted attention in the fields of biology and environmental science. Further analysis of confocal fluorescence microscopy images and the MTT assay indicated that the conjugated ND probe has favorable biocompatibility and low toxicity. This new Cu2+ and NO selective fluorescent ND probe may have potential applications in environmental science and biology.

Spectroscopic analysis of the interaction between gallium(III) and apoovotransferrin

Ovotransferrin is a main member of transferrin family and has a dual role in both the transport of iron and antibacterial function. Gallium-67 is widely used as an imaging agent for tumors. It has been reported that Ga(3+) can bind to apoovotransferrin at two sites, one in the N-terminal lobe and another in the C-terminal lobe. However, several details of the interaction between Ga(3+) and apoOTf remain unclear. Here, we report detailed investigations into the interactions of Ga(3+) with apoovotransferrin at the molecular level. First, the characteristics of Ga(3+) binding to apoovotransferrin were analyzed using UV difference spectra. The results show that Ga(3+) prefers to bind to the N-terminal site rather than the C-terminal site under the experimental conditions. Effective stability constants of logK(N)=18.88+/-0.24 and logK(C)=17.65+/-0.12 were determined. Second, conformational changes in apoovotransferrin during Ga(3+) binding were studied using 2-p-toluidinylnaphthalene-6-sulfonate (TNS) as a fluorescence probe. Apoovotransferrin undergoes a large conformational change when Ga(3+) binds to the N-terminal site, and a smaller conformational change when the ion binds to the C-terminal site. UV difference spectra were also used to measure the rate at which EDTA removes Ga(3+) from ovotransferrin carrying one Ga(3+) at the N-terminal site. Ga(3+) removal from the N-terminal binding site follows simple saturation kinetics.

Chemical properties and biotoxicity of several chromium picolinate derivatives

As a man-made additive, chromium picolinate Cr(pic)3 has become a popular dietary supplement worldwide. In this paper Cr(pic)3 and its new derivatives Cr(6-CH3-pic)3 (1), [Cr(6-NH2-pic)2(H2O)2]NO3 (2) and Cr(3-NH2-pic)3 (3) were synthesized, and complexes 1 and 2 were characterized by X-ray crystal structure (where pic=2-carboxypyridine). The relationship between the chemical properties and biotoxicity of these complexes was fully discussed: (1) The dynamics stability of chromium picolinate complexes mainly depends on the CrN bonds length. (2) There is a positive correlation between the dynamics stability, electrochemical potentials and generation of reactive oxygen species through Fenton-like reaction. (3) However, no biological toxicity was observed through MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and sub-chronic oral toxicity study for these chromium picolinate compounds. Together, our findings establish a framework for understanding the structure-property-toxicity relationships of the chromium picolinate complexes.

The photochromism, light harvesting and self-assembly activity of a multi-function Schiff-base compound based on the AIE effect

Aggregation-induced emission (AIE) luminogens with photochromic properties show strong potential in molecular switches, photo-controllable materials, photo-patterning, etc. In this paper one Schiff-base compound 1 exhibited reversible photo-controllable colour changes in solid states due to the typical ESIPT effect: the crystal turned from colourless to yellow after ultraviolet light irradiation and became colourless again in the dark. Second, 1 presented a good aggregation-induced emission (AIE) activity in aqueous solution. Third, highly efficient light-harvesting systems are successfully fabricated in aqueous solution based on AIE(1) and rhodamine B, where AIE(1) acts as an energy donor and rhodamine B acts as an acceptor. Fourth, addition of Al3+ or Cu2+ ions destructed the N⋯H–O hydrogen bond and induced the rearrangement or destruction of AIE(1) with a different emission. Last, theoretical calculations of deprotonated 1 indicated that the protons on phenolic hydroxyl groups have a great influence on the fluorescence properties of 1. These results demonstrated that compound 1 is a multi-functional organic luminescent material exhibiting excellent photochromism, light-harvesting and AIE properties.

Two colorimetric and ratiometric fluorescence probes for hydrogen sulfide based on AIE strategy of α–cyanostilbenes

Aggregation-induced emission (AIE) active fluorescent probes have attracted great potential in biological sensors. In this paper two cyanostilbene based fluorescence chemoprobe Cya-NO2 (1) and Cya-N3 (2) were developed and evaluated for the selective and sensitive detection of hydrogen sulfide (H2S). Both of these probes behave aggression-induced emission (AIE) activity which fluoresces in the red region with a large Stokes shift. They exhibit rapid response to H2S with enormous colorimetric and ratiometric fluorescent changes. They are readily employed for assessing intracellular H2S levels.

Assembly and disassembly activity of two AIEE model compounds and its potential application

Aggregation-induced emission (AIE) has received great attention. In this paper, Cu2+ induced self-assembly and H2S induced disassembly of two aggregation-induced emission enhancement (AIEE) compounds were reported in this paper. Two salicylaldehyde azine Schiff base were synthesized and characterized. It is found that 1 and 2 are AIEE active molecular both in aqueous solution and crystal state with strong yellow fluorescence. Theirs fluorescence can be selectively quenched in the presence of Cu2+ ions with the formation of self-assembly system [1-Cu2+]n. The interaction mechanism has been researched by multiple means. Depending on this reaction, energy changes (ΔG) from 1 to [1-Cu2+]n was also estimated by Scatchard formula. Moreover, the quenching fluorescence was further restored by H2S both in tube and live cells along with the releasing of AIEE molecular 1. That is, a reversible process between AIEE, self-assembly and disaggregation can be found in the model compound.