Facile synthesis of magnetic intelligent sensors for the pH-sensitive controlled capture of Cr(vi).

In this work, intelligent pH-sensitive sensors (Fe3O4/RhB@PAM) for Cr(vi) detection were successfully synthesized based on polyacrylamide (PAM) and Rhodamine B (RhB) co-modified Fe3O4 nanocomposites. The characterization results indicated that the sensors had many favorable properties, including suitable size, stable crystal structure and excellent magnetic response performance (47.59 emu g-1). In addition, the fluorescence changes during the detection process indicated that Fe3O4/RhB@PAM were "ON-OFF" intelligent sensors. When the Fe3O4/RhB@PAM sensors were placed in acidic Cr(vi) solution (pH 4), PAM acted as a pH-responsive "gatekeeper" releasing RhB, and the fluorescence intensity of released RhB was weakened by the complexation of Cr(vi). Furthermore, the fluorescence changes of the magnetic sensors were remarkably specific for Cr(vi) even in the presence of other competitive cations, and the limit of detection (LOD) for Cr(vi) was lower (0.347 µM) than the value recommended by the World Health Organization (0.96 µM). All the results presented in this study showed that the Fe3O4/RhB@PAM sensors had significant potential for Cr(vi) detection in acidic environmental samples.

Synthesis and characterization of magnetic polymeric nanocomposites for pH-sensitive controlled release of methotrexate.

As one of the well-known anticancer drugs, methotrexate (MTX) has been limited in clinical application due to its side effects on normal tissues. This study focused on the one-step hydrothermal synthesis and in vitro evaluation of Fe3O4/RGO-PEI as MTX carriers for targeted anticancer therapy. In which, the Fe3O4 provided magnetic response properties; RGO acted as a stage for Fe3O4 loading and improved the dispersion of Fe3O4; polyethylenimine (PEI) was used as a surface modifier and a storehouse for MTX. The prepared Fe3O4/RGO-PEI nanocomposites exhibited a suitable size, good stability and magnetic responsibility. And the MTX loading content and loading efficiency were calculated to be 26.6% and 90.5%, respectively. What's more, due to the diffusion and dissolution of PEI, the Fe3O4/RGO-PEI-MTX exhibited excellent pH-sensitivity, the values of MTX release rate (%) within 48 h at pH 5.8 and 4.0 were 64.3% and 87.4%, respectively. Furthermore, MTT assays in cancer cells (HepG2) and normal cells (HUVEC) demonstrated that Fe3O4/RGO-PEI-MTX exhibited high anticancer activity while low toxicity to normal cells, and also the Fe3O4/RGO-PEI composites were practically non-toxic. Thus, our results revealed that Fe3O4/RGO-PEI-MTX would be a competitive candidate for targeted delivery and controlled release of MTX.

pH-sensitive magnetic drug delivery system via layer-by-layer self-assembly of CS/PEG and its controlled release of DOX.

Cancer is one of the biggest killers threat to human life and health and is still difficult to treat mainly due to the lack of targeted drug delivery stages and limitations associated with delivering drugs to targeted cancer tissues. The goal of this work was to develop a magnetic, pH-sensitive formulation for targeted delivery of chemotherapeutic agents to cancer cells. Then the functional drug delivery system (Fe3O4@CS/PEG-DOX) was synthesized by the layer-by-layer (LbL) self-assembly technique. And the drug loading content is calculated to be 19.1%. In addition, the Fe3O4@CS/PEG-DOX exhibited excellent pH-sensitivity, 73.1% DOX was released within 48 h at pH 4.0. Furthermore, all the release behaviors fit the Higuchi model very well and the dissolution of CS/PEG layers played a key role on DOX release from Fe3O4@CS/PEG-DOX. The results of toxicity analysis in human liver hepatocellular carcinoma cells (HepG2) revealed that Fe3O4@CS/PEG-DOX exhibited high anti-tumor activity, while the Fe3O4@CS/PEG nanocomposites were practically non-toxic. Therefore, all the results demonstrated that the Fe3O4@CS/PEG-DOX could have an important impact on the development of targeted intracellular delivery nanodevices for cancer therapy.

Biosynthesis of (S)-4-chloro-3-hydroxybutanoate ethyl using Escherichia coli co-expressing a novel NADH-dependent carbonyl reductase and a glucose dehydrogenase.

A novel NADH-dependent carbonyl reductase (PsCR II) gene with an open reading frame of 855bp encoding 285 amino acids was cloned from Pichia stipitis. Analysis of the amino acid sequence of PsCR II revealed less than 55% identity to known reductases that produce (S)-4-chloro-3-hydroxybutanoates ethyl [(S)-CHBE]. When NADH was provided as an electron donor, Escherichia coli with pET-22b-PsCRII exhibited an activity of 15U/mg protein using 4-chloro-3-oxobutanoate ethyl (COBE) as a substrate. This activity was the highest ever reported for reductases, with the exception of PsCR I, which in our previous analysis required NADPH for catalysis. Biocatalysis of COBE to (S)-CHBE was investigated using E. coli with a polycistronic plasmid pET-BP II co-expressing PsCR II and a glucose dehydrogenase in a water/butyl acetate system for 24h. The transformants gave a molar yield of 91%, and an optical purity of the (S)-isomer of higher than 99% enantiomeric excess.