Nickel-Catalyzed C(sp3)-O Hydrogenolysis via a Remote-Concerted Oxidative Addition and Its Application to Degradation of a Bisphenol A-Based Epoxy Resin.

In this work, we developed a nickel-catalyzed transfer hydrogenolysis of 1-aryloxy-3-amino-2-propanols, which is a model compound of an amine-cured bisphenol A (BPA)-based epoxy resin. Mechanistic investigation revealed that the hydroxy group acts as the hydrogen donor to generate α-aryloxy ketone, which undergoes an unprecedented remote-concerted oxidative addition of the C(sp3)-O bond as suggested by DFT calculation. Successful application of this method was demonstrated by the degradation of a diamine-cured BPA-based epoxy resin, in which BPA was directly recovered from the resin.

Rational design of a ratiometric fluorescent aptasensor for patulin in traditional Chinese medicine through the studies of the interaction mechanism between its DNA aptamer and the target molecule.

Patulin (PAT) is a kind of mycotoxin which must be monitored for the sake of quality and safety in traditional Chinese medicine (TCM) owing to its harm to human health. On this account, a rationally designed ratiometric fluorescent aptasensor was developed based on the studies of the interaction mechanism between PAT and its aptamer (PAT-APT). First, CD spectroscopy, molecular docking, and molecular dynamic simulation were applied to investigate the details on how PAT-APT binds with its target molecule. The results indicated that the structure of PAT-APT changed to a certain extent and was stabilized after binding with PAT. C-11, C-37 and C-38 were the key sites for the recognition and interaction between PAT-APT and its target. Second, based on these results, a ratiometric aptasensor was designed using fluorescence resonance energy transfer (FRET) and synchronous fluorescence spectroscopy. A complementary sequence (cDNA) to the aptamer with an appropriate length and hybridization position was obtained through rational design and optimization. Both PAT-APT and cDNA were labeled using a pair of fluorophores, which could generate FRET when the two single-stranded oligonucleotides hybridized. The accurate detection of PAT could be realized according to the change ratio of the fluorescence intensity at the corresponding wavelengths of the two fluorophores before and after the assay. The aptasensor achieved an ultralow limit of detection of 0.16 nM, perfect selectivity, and satisfactory practicability in complex TCM samples. To our knowledge, this is the first aptasensor for PAT designed through the interaction mechanism between its aptamer and the target molecule. Moreover, the assay for PAT is cost-effective, does not need complicated pretreatment and only takes less than an hour. In summary, this study makes a contribution to the safety control of TCM and provides a thinking mode from mechanism to rational design to conquer the problem of sensitive aptasensing of one component in a complex system.

Response of Cd, Zn Translocation and Distribution to Organic Acids Heterogeneity in Brassica juncea L.

In order to investigate the translocation, distribution, and organic acid heterogeneity characteristics in Brassica juncea L., a pot experiment with the exogenous application of Cd and Zn was conducted to analyze the effects of Cd, Zn, and organic acid contents and heterogeneity on the translocation and distribution of Cd and Zn. The results showed that the Cd and Zn contents of B. juncea were mainly accumulated in the roots. The Cd content in the symplast sap was 127.66-146.50% higher than that in the apoplast sap, while the opposite was true for Zn. The distribution of Cd in xylem sap occupied 64.60% under 20 mg kg-1 Cd treatment, and Zn in xylem sap occupied 60.14% under 100 mg kg-1 Zn treatment. The Cd was predominantly distributed in the vacuole, but the Zn was predominantly distributed in the cell walls. In addition, oxalic and malic acids were present in high concentrations in B. juncea. In the vacuole, correlation analysis showed that the contents of Cd were negatively correlated with the contents of oxalic acid and succinic acid, and the contents of Zn were positively correlated with the contents of malic acid and acetic acid. The contents of Cd and Zn were negatively related to the contents of oxalic acid and citric acid in xylem sap. Therefore, Cd in B. juncea was mainly absorbed through the symplast pathway, and Zn was mainly absorbed through the apoplast pathway, and then Cd and Zn were distributed in the vacuole and cell walls. The Cd and Zn in B. juncea are transferred upward through the xylem and promoted by oxalic acid, malic acid, and citric acid.

Fluorescence-based aptasensors for small molecular food contaminants: From energy transfer to optical polarization.

Small molecular food contaminants, such as mycotoxins, pesticide residues and antibiotics, are highly probable to be passively introduced in food at all stages of its processing, including planting, harvest, production, transportation and storage. Owing to the high risks caused by the unknowing intake and accumulation in human, there is an urgent need to develop rapid, sensitive and efficient methods to monitor them. Fluorescence-based aptasensors provide a promising platform for this area owing to its simple operation, high sensitivity, wide application range and economical practicability. In this paper, the common sorts of small molecular contaminants in foods, namely mycotoxins, pesticides, antibiotics, etc, are briefly introduced. Then, we make a comprehensive review, from fluorescence resonance energy transfer (in turn-on, turn-off, and ratiometric mode, as well as energy upconversion) to fluorescence polarization, of the fluorescence-based aptasensors for the determination of these food contaminants reported in the last five years. The principle of signal generation, the advances of each sort of fluorescent aptasensors, as well as their applications are introduced in detail. Additionally, we also discussed the challenges and perspectives of the fluorescent aptasensors for small molecular food contaminants. This work will offer systematic overview and inspiration for amateurs, researchers and developers of fluorescence-based aptasensors for the detection of small molecules.

LAMP-H+-responsive electrochemical ratiometric biosensor with minimized background signal for highly sensitive assay of specific short-stranded DNA.

Herein, the sequence-specific short-stranded biomarker DNA (hDNA, 21-nt) is acted as targeting out-primer to implement the loop-mediated isothermal amplification for releasing hydrogen ions (LAMP-H+). Using LAMP-H+ as signaling transducer, we report a highly sensitive electrochemical ratiometric biosensor for hDNA with minimized background signal, which is achieved via magnetic separation using AuNPs-modified Fe3O4 (Au@Fe3O4) as micro-reactor. In Au@Fe3O4, a double-stranded complex of a pH-responsible strand (I*) and a substrate strand (S*) is bound via Au-N bonds, where the treatment with LAMP-H+ leads to I* folding into i-motif conformation and S* dehybridization. The S* further hybridizes a catalytic strand (C*) to assemble Mg2+-DNAzymes that are cleaved by Mg2+, releasing C* for repeated formation and robust nicking of Mg2+-DNAzymes. The resultant output fuel strands (F*) are introduced in a modified electrode to drive the strand displacement of two hairpins individually labeled with two electron mediators. Through F*-mediated recycled amplification, the ratio of their electrochemical currents changed in opposite is highly sensitive to the varied hDNA down to 2.1 fM. By integrating LAMP-H+-stimulated i-motif switching with Mg2+-DNAzyme cleavage, this logic transduction of LAMP-H+(i-motif/Mg2+-DNAzyme)F* efficiently minimizes the inherent background of traditional LAMP-based assays. Resultantly, our electrochemical ratiometric strategy would be applicable to diverse short-stranded DNAs or even RNAs as targeting primers of LAMP.