Retraction Note: Impact of different promoters, promoter mutation, and an enhancer on recombinant protein expression in CHO cells.

This paper has been retracted at the request of the authors.

Impact of different promoters, promoter mutation, and an enhancer on recombinant protein expression in CHO cells.

In the present study, six commonly used promoters, including cytomegalovirus major immediate-early (CMV), the CMV enhancer fused to the chicken beta-actin promoter (CAG), human elongation factor-1α (HEF-1α), mouse cytomegalovirus (mouse CMV), Chinese hamster elongation factor-1α (CHEF-1α), and phosphoglycerate kinase (PGK), a CMV promoter mutant and a CAG enhancer, were evaluated to determine their effects on transgene expression and stability in transfected CHO cells. The promoters and enhancer were cloned or synthesized, and mutation at C-404 in the CMV promoter was generated; then all elements were transfected into CHO cells. Stably transfected CHO cells were identified via screening under the selection pressure of G418. Flow cytometry, qPCR, and qRT-PCR were used to explore eGFP expression levels, gene copy number, and mRNA expression levels, respectively. Furthermore, the erythropoietin (EPO) gene was used to test the selected strong promoter. Of the six promoters, the CHEF-1α promoter yielded the highest transgene expression levels, whereas the CMV promoter maintained transgene expression more stably during long-term culture of cells. We conclude that CHEF-1α promoter conferred higher level of EPO expression in CHO cells, but the CMV promoter with its high levels of stability performs best in this vector system.

The anion recognition properties of hydrazone derivatives containing anthracene.

A series of artificial receptors, hydrazone derivatives containing anthracene, have been designed and synthesized. The interaction of these receptors with biologically important anions was determined by UV-vis, fluorescence and 1H NMR titration experiments and theoretical investigation. Results indicate that the receptor (1) without NO2 shows no binding ability for various anions. The other receptors (2 and 3) show the highest binding ability for acetate (AcO-) among studied anions (fluoride (F-), dihydrogen phosphate (H2PO4-), chloride (Cl-), bromide (Br-), iodide (I-)); and the binding ability for AcO- is not interfered by the existence of other anions. The additions of AcO-, F- and H2PO4- can arouse different degrees of fluorescence quenching. 1H NMR titration shows that the interaction between the receptor 2 and F- firstly depends on the hydrogen-bond formation; later the interacted site NH is deprotonated and the added F- forms hydrogen bond with the near CH in Schiff base. Moreover, visual color changes accompany guest binding, enabling this system to act as colorimetric anion sensors.

Anion recognition and sensing of ruthenium(II) and cobalt(II) sulfonamido complexes.

A series of artificial receptors, based on a sulfonamido system, have been designed and synthesized. The interaction of these receptors with biologically important anions was determined by UV-vis, (1)H NMR titration and electrochemical experiments. Results indicate that these receptors show high recognition abilities for fluoride (F(-)) or acetate (AcO(-)), moderate affinities for dihydrogen phosphate (H(2)PO(4)(-)) or hydroxyl (OH(-)) and almost no affinities for chloride (Cl(-)), bromide (Br(-)) or iodide (I(-)). (1)H NMR titration shows that the interaction between the receptors and anions depends on the hydrogen-bond formation. The Co(III)/Co(II) redox signals of receptor and disappear gradually when the fluoride or acetate anions are added. Moreover, visual color changes accompany guest binding, enabling this system to act as colorimetric anion sensors. The colorimetric properties of these sensors are ascribed to the hydrogen-bond formation and the colorimetric group quinoxaline.

The anion recognition properties of Schiff base or its reductive system based on 2,2'-bipyridine derivatives.

Two novel artificial receptors, 2,2'-bipyridine derivatives containing phenol group, have been designed and synthesized. The interaction of the receptors containing Schiff base or its reductive system with biologically important anions was determined by UV-vis and (1)H NMR titration experiments. Results indicate that receptors 1 and 2 show the strong binding ability for dihydrogen phosphate (H(2)PO(4)(-)), fluoride (F(-)), acetate (AcO(-)) and almost no binding ability for chloride (Cl(-)), bromide (Br(-)), iodide (I(-)). At the same time, the strongest binding ability of receptor 1 for H(2)PO(4)(-) among studied anions is not influenced by the existence of other anions; as well as receptor 2 for F(-). In addition, the binding ability of receptor 1 (Schiff base system) with various anions is stronger than that of receptor 2 (the reductive Schiff base system) due to the difference of electronic effect.

Studies on synthesis and anion recognition properties of (3'-nitrobenzo)[2,3-d]-(3''-nitrobenzo)[9,10-d]-1,4,8,11-tetraazacyclotetradecane-5,7,12,14-tetraone.

A novel artificial receptor, (3'-nitrobenzo)[2,3-d]-(3''-nitrobenzo)[9,10-d]-1,4,8,11-tetraazacyclotetradecane-5,7,12,14-tetraone, was designed and synthesized. The interactions of this receptor with different anions were determined by UV-vis and (1)H NMR titration experiments, and their affinity constants to different anions were compared with those of other similar/different systems. The results indicated that this receptor showed a high selective and recognitive ability for F(-) among F(-), Cl(-), Br(-), I(-), AcO(-), OH(-), and H(2)PO(4)(-). Moreover, the low energy configuration of this receptor was further determined by means of theoretical investigations.

Effects of the receptors bearing phenol group and copper(II) on the anion recognition and their analytical application.

Two novel artificial receptors based on diamide and bearing phenol group and copper(II) have been synthesized. Their anion-binding properties are evaluated for F(-), Cl(-), Br(-), I(-), AcO(-), H(2)PO(4)(-) and OH(-) by UV-vis and (1)H NMR titration experiments to further elucidate the impact of phenol group and copper(II) on the chemistry of anion-recognition. Results indicate that the interacted model of fluoride anion with receptor 1 is different from other anions and the (1)H NMR signals of receptor 2 occur changes after the addition of fluoride anion. This may be related with the small radius and strong electronegative property of fluoride. The receptors should have many chemical and analytical applications and the sensing principle should be widely applicable to the sensing of other receptors.