Highly Iso-Selective and Active Catalysts of Sodium and Potassium Monophenoxides Capped by a Crown Ether for the Ring-Opening Polymerization of <i>rac</i>-Lactide

Sodium and potassium complexes supported by a bulky monophenoxy with one xanthenyl group at the ortho-position and 18-crown-6 or 15-crown-5 as an auxiliary ligand were synthesized and characterized. These complexes are highly iso-selective and active catalysts for the controlled ring-opening polymerization of <i>rac</i>-lactide. The best isotacticity (<i>P</i>_m) achieved was 0.86, which is the highest iso-selectivity reported to date for an alkali-metal complex. In addition, the corresponding polymer exhibited a high <i>T</i>_m of 182 °C. Furthermore, the polymerization looks like an anti-Arrhenius reaction, which is slower at high temperatures than at low temperatures

Effect of 5-FU on the viability and morphological changes of A549 cells.

<p>(A) Cell viability was determined by MTT assay after treatment with different concentrations of 5-FU for 24 h and 48 h. IC50 was calculated by IC50 software program. (B) Morphological changes was observed after treating cells with 10 µmol/L 5-FU for 48 h by Inverted microscope(Olympus, Japan). All data are representative of at least three independent experiments.</p

3-MA increases the apoptotic cell death induced by 5-FU.

<p>Cells were pretreated with 5 mmol/L 3-MA for 1 h before exposure to 10 µmol/L 5-FU for 48 h. (A) The cell viability was measured with an MTT assay. Data represent means of four independent experiments. (B) Cell death rate was analyzed by the Annexin V assay by flow cytometry as described in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056679#s2" target="_blank">Materials and methods</a>. (C) Cell lysates were prepared and subjected to immunoblotting with antibodies to caspase-9, caspase-8, caspase-3, PARP, and β-actin. All data are representative of at least three independent experiments.</p

Induction of autophagy in A549 cells by 5-FU treatment.

<p>A549 cells were treated with 10 µmol/L 5-FU for different time as indicated, then the autophagosomes and the autophagic levels were detected. (A) The formation of autophagosomes in treated cells were checked by TEM. (B)LC3, Beclin-1 and p62 were examined by western blot. β-actin was a loading control. All data are representative of at least three independent experiments.</p

Inhibition of autophagy by Atg7 siRNA increases the apoptotic cell death to 5-FU.

<p>Cells were transfected with Atg7-targeted siRNA and the Control siRNA for 24 h before exposure to 10 mmol/L 5-FU for 48 h. (A) Cell lysates were prepared and subjected to immunoblotting with antibodies to LC3, Atg7, PARP, and b-actin. (B) Cell viability was measured using MTT assay. (C) Apoptotic cell death was analyzed by the Annexin V/PI assay. All data are representative of at least three independent experiments.</p

The effect of 3-MA on cell autophagy.

<p>Cells were pretreated with 5 mmol/L 3-MA for 1 h before exposure to 10 µmol/L 5-FU for 48 h, then acridine orange was used to stain AVOs, the fluorescence-activated cells were analyzed by flow cytometry (A). After treatment the cells were stained with acridine orange for AVO observation. The cells were visualized under a red filter fluorescence microscope(B). TO quantification of cells developing AVO in A549 cells, the percentage of developed AVOs was calculated based on the results of fluorescence-activated cell sorting assay(C). Fluorescent microscope by immunofluorescence staining for LC3 in the treated-A549 cells(D). Western blot analysis was carried out to detect LC3 protein levels. Blots were re-proved with anti-β-actin as a loading control(E). All data are representative of at least three independent experiments.</p

Inhibit autophagy by 3-MA stimulates ROS formation which is required for sensitization of A549 cells to 5-FU-induced apoptosis.

<p>Cells were pretreated with 10 mM NAC for 1 h prior to 10 µmol/L 5-FU (48 h) treatment in the presence or absence of 3-MA. (A)The ROS generation was detected using DCFDA by a flow cytometer. Data were processed with the CellQuest software and analyzed by densitometry. (B)Cell death was measured by Annexin V/PI staining. (C)Caspase-3 activity assay was performed as described in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056679#s2" target="_blank">Materials and Methods</a>. (D)The cyt-c level in cytosol fraction was detected by immunoblotting. All data are representative of at least three independent experiments.</p

Effect of 3-MA on the cytochrome c release and MMP change by 5-FU treatment.

<p>Cells were treated as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056679#pone-0056679-g003" target="_blank">Fig. 3</a>. (A)The mitochondria and the cytosol fractions were isolated as described in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056679#s2" target="_blank">Materials and methods</a>, and then were subjected to immunoblotting for the detection of cytochrome c. (B)The MMP change was assessed by JC-1 staining by flow cytometry as described in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056679#s2" target="_blank">Materials and methods</a>. All data are representative of at least three independent experiments.</p

Synthesis and Characterization of Multi-Alkali-Metal Tetraphenolates and Application in Ring-Opening Polymerization of Lactide

A series of alkali metal complexes supported by two bulky tetraphenols were synthesized and characterized. The reactions of α,α,α′,α′-tetra­(3,5-di-<i>tert</i>-butyl-2-hydroxyphenyl)-<i>p</i>-xylene­(<i>para</i>-tetraphenol) with ^<i>n</i>BuLi, sodium, and KSi­(NMe₂)₃ gave bimetallic complexes <b>1</b>, <b>2</b>, and <b>3</b>, respectively. Treatments of the α,α,α′,α′-tetra­(3,5-di-<i>tert</i>-butyl-2-hydroxyphenyl)-<i>m</i>-xylene­(<i>meta</i>-tetraphenol) with 2 or 4 equiv of ^<i>n</i>BuLi afforded complexes <b>4</b> or <b>5</b>, while the reactions of <i>meta</i>-tetraphenol with sodium and KSi­(NMe₂)₃ gave only trimetallic complexes <b>6</b> and <b>7</b> for the additional p−π interaction. Complexes <b>1</b>–<b>7</b> were all characterized by single-crystal X-ray diffraction techniques. In the presence of benzyl alcohol, all complexes are active catalysts for the ring-opening polymerization of l-lactide. Comparatively, bimetallic complexes <b>1</b>, <b>2</b>, and <b>3</b> are more efficient catalysts because of their symmetric structures, in which complex <b>3</b> presents as a rare highly active potassium catalyst for the ring-opening polymerization of lactide, leading to polymers with good molecular weight control and narrow molecular weight distributions

Electrosynthesis of Trisubstituted 2‑Oxazolines via Dehydrogenative Cyclization of β‑Amino Arylketones

An electrochemically intramolecular functionalization of C­(sp³)–H bonds with masked oxygen nucleophiles was developed. With KI as the catalyst and electrolyte, diverse trisubstituted 2-oxazolines were constructed in good to excellent yields. This newly developed electrochemical dehydrogenative approach features external oxidant-free and additive-free conditions