Photochemical Carbon Dioxide Capture and Conversion by Metal-Organic Frameworks

Although photocatalytic CO2 reduction using several zirconium metal-organic frameworks (MOFs) has been reported, mechanistic understanding of photocatalytic CO2 reduction in zirconium MOFs with photoresponsive ligands is lacking. An often proposed generalized pathway involving ligand-to-metal charge transfer to form high energy Zr(III) intermediates is inconsistent with ligand-centered frontier orbitals. The mechanism of photochemical CO2 reduction to formate by PCN-136, a Zr-based metal−organic framework (MOF) that incorporates light-harvesting nanographene ligands, has been investigated using steady-state and time-resolved spectroscopy and density functional theory (DFT) calculations. The catalysis was found to proceed via a “photoreactive capture” mechanism, where Zr-based nodes serve to capture CO2 in the form of Zr-bicarbonates, while the nanographene ligands have a dual role of absorbing light and storing one-electron equivalents for catalysis. We also find that the process occurs via a “two-for-one” route, where a single photon initiates a cascade of electron/hydrogen atom transfers from the sacrificial donor to the CO2-bound MOF. Direct photoreduction of MOF-bound bicarbonate to formate provides further support of the proposed mechanism. The new mechanism proposed in this study elucidates a low-energy photoreactive CO2 capture pathway with an energy barrier surmountable by visible light and may henceforth provide guidance for the design of CO2 reduction MOF photocatalysts. In a follow-up study, we demonstrate a facile approach to optical gap tuning via postsynthetic modifications of pbz-MOF-1, a Zr-based MOF with polyphenylene ligands. A simple reaction of pbz-MOF-1 with FeCl3 was shown to induce three different chemical reactions: oxidative dehydrogenation, chlorination, and one-electron oxidation of the ligands. The result of these reactions was a gradual decrease in the optical gap from 2.95 eV to as little as 0.69 eV. Steady-state and time-resolved optical spectroscopy, mass spectrometry, and electron paramagnetic resonance spectroscopy, coupled with density functional theory calculations, provide insights into the chemical transformations that affect the optical properties of the MOF. In a latest study, we synthesized a new MOF using a ligand with a perchlorinated, contorted hexabenzocoronene core. Preliminary transient absorption studies on the Zr-MOF show long-lived excited states. Additionally, the light-responsive Zr-MOF has been shown to photochemically reduce CO2 to CO and formate

An Aliphatic Solvent-Soluble Lithium Salt of the Perhalogenated Weakly Coordinating Anion [Al(OC(CCl₃)(CF₃)₂)₄]⁻

The facile synthesis of a new highly aliphatic solvent-soluble Li⁺ salt of the perhalogenated weakly coordinating anion [Al­(OC­(CCl₃)­(CF₃)₂)₄]⁻ and its application in stabilizing the Ph₃C⁺ cation were investigated. The lithium salt Li­[Al­(OC­(CCl₃)­(CF₃)₂)₄] (<b>4</b>) was prepared by the treatment of 4 mol equiv of HOC­(CCl₃)­(CF₃)₂ with purified LiAlH₄ in <i>n</i>-hexane from −20 °C to room temperature. Compound <b>4</b> is highly soluble in both polar and nonpolar solvents, and it bears both CCl₃ and CF₃ groups, resulting in a lower symmetry around the Al center compared to that of Li­[Al­(OC­(CF₃)₃)₄] (<b>1</b>). Treatment of <b>4</b> with Ph₃CCl afforded the ionic compound [Ph₃C]­[Al­(OC­(CCl₃)­(CF₃)₂)₄] (<b>5</b>) bearing the Ph₃C⁺ cation with concomitant elimination of LiCl, suggesting the potential application of [Al­(OC­(CCl₃)­(CF₃)₂)₄]⁻ in stabilizing reactive cationic species. Compounds <b>4</b> and <b>5</b> were fully characterized by spectroscopic and structural methods

Caveolin-1 Is Up-Regulated by GLI1 and Contributes to GLI1-Driven EMT in Hepatocellular Carcinoma

<div><p>Caveolin-1 (Cav-1) has been recently identified to be over-expressed in hepatocellular carcinoma (HCC) and promote HCC cell motility and invasion ability via inducing epithelial-mesenchymal transition (EMT). However, the mechanism of aberrant overexpression of Cav-1 remains vague. Here, we observed that Cav-1 expression was positively associated with GLI1 expression in HCC tissues. Forced expression of GLI1 up-regulated Cav-1 in Huh7 cells, while knockdown of GLI1 decreased expression of Cav-1 in SNU449 cells. Additionally, silencing Cav-1 abolished GLI1-induced EMT of Huh7 cells. The correlation between GLI1 and Cav-1 was confirmed in tumor specimens from HCC patients and Cav-1 was found to be associated with poor prognosis after hepatic resection. The relationship between protein expression of GLI1 and Cav-1 was also established in HCC xenografts of nude mice. These results suggest that GLI1 may be attributed to Cav-1 up-regulation which plays an important role in GLI1-driven EMT phenotype in HCC.</p></div

GLI1 was found to promote growth of Huh7 xenografts and result in more Cav-1 expression and EMT phenotype in Huh7 xenograft tissues.

<p>(A) The size of xenografts from Huh7 GLI1 group was significantly larger than one from Huh7 Vector group (P = 0.002); (B) The representative IHC staining of Cav-1 in xenografts from both Huh7 GLI1 group (a) and Huh7 Vector group (b). Cav-1 protein was detected in both cell membrane (as labelled by a black arrow) and cytoplasm (as labelled by a white arrow). Cav-1 expression in xenografts from Huh7 GLI1 group was apparently more than one in xenografts from Huh7 Vector group; (C) The representative IHC staining of E-cadherin in xenografts from both Huh7 GLI1 group (a) and Huh7 Vector group (b). E-cadherin protein located mainly in cell membrane, as labelled by black arrows. There were less E-cadherin expression in xenograft tissues from Huh7 GLI1 group than ones from Huh7 Vector group; (D) The representative IHC staining of N-cadherin in xenografts from both Huh7 GLI1 group (a) and Huh7 Vector group (b). N-cadherin expression expressing basically in cytoplasm (labelled by white arrows) was increased clearly in xenograft parenchymal tissues from Huh7 GLI1 group than ones from Huh7 Vector group. Cytoplasmic N-cadherin expression was also found in xenograft mesenchymal tissues from both groups, as labelled by black arrows.</p

Characterization of an Archaeal Two-Component System That Regulates Methanogenesis in <i>Methanosaeta harundinacea</i>

<div><p>Two-component signal transduction systems (TCSs) are a major mechanism used by bacteria in response to environmental changes. Although many sequenced archaeal genomes encode TCSs, they remain poorly understood. Previously, we reported that a methanogenic archaeon, <i>Methanosaeta harundinacea</i>, encodes FilI, which synthesizes carboxyl-acyl homoserine lactones, to regulate transitions of cellular morphology and carbon metabolic fluxes. Here, we report that <i>filI</i>, the cotranscribed <i>filR2</i>, and the adjacent <i>filR1</i> constitute an archaeal TCS. FilI possesses a cytoplasmic kinase domain (histidine kinase A and histidine kinase-like ATPase) and its cognate response regulator. FilR1 carries a receiver (REC) domain coupled with an ArsR-related domain with potential DNA-binding ability, while FilR2 carries only a REC domain. In a phosphorelay assay, FilI was autophosphorylated and specifically transferred the phosphoryl group to FilR1 and FilR2, confirming that the three formed a cognate TCS. Through chromatin immunoprecipitation–quantitative polymerase chain reaction (ChIP-qPCR) using an anti-FilR1 antibody, FilR1 was shown to form <i>in vivo</i> associations with its own promoter and the promoter of the <i>filI-filR2</i> operon, demonstrating a regulatory pattern common among TCSs. ChIP-qPCR also detected FilR1 associations with key genes involved in acetoclastic methanogenesis, <i>acs4</i> and <i>acs1</i>. Electrophoretic mobility shift assays confirmed the <i>in vitro</i> tight binding of FilR1 to its own promoter and those of <i>filI-filR2</i>, <i>acs4</i>, and <i>mtrABC</i>. This also proves the DNA-binding ability of the ArsR-related domain, which is found primarily in Archaea. The archaeal promoters of <i>acs4</i>, <i>filI</i>, <i>acs1</i>, and <i>mtrABC</i> also initiated FilR1-modulated expression in an <i>Escherichia coli lux</i> reporter system, suggesting that FilR1 can up-regulate both archaeal and bacterial transcription. In conclusion, this work identifies an archaeal FilI/FilRs TCS that regulates the methanogenesis of <i>M. harundinacea</i>.</p></div

EMSAs showed FilR1 binding to the promoters of its own and the operon <i>filI-filR2</i>.

<p>Purified recombinant FilR1 protein was incubated with 0.5-labeled DNA in the standard binding reaction mixture at 25°C for 20 min, and then run on a native PAGE. Concentration of purified FilR1 protein was shown at the top of each lane. Unlabeled <i>filI-filR2</i> promoter (NP<i>_filI-filR2</i>) was used as a competitor substrate of FilR1, which was added at the final concentrations of 5, 25, 125 and 250 nM in lane 6 and 15, 7 and 16, 8 and 17, and 9 and 18, respectively. (A) P<i>_filI-R2</i>, promoter of the <i>filI-filR2</i> operon; (B) P<i>_filR1</i>, promoter of <i>filR1</i>, and (C) U<i>_filI</i>, an internal DNA fragment of gene <i>filI</i>.</p

ChIP assays showed FilR1 binding to the promoters of its own (P<i>_filR1</i>) and <i>filI-filR2</i> operon (P<i>_filR1-filR2</i>) inside the cells of <i>M. hurandiacea</i> 6AC.

<p>(A) PCR products of the promoters of its own (P<i>_filR1</i>) and <i>filI-filR2</i> operon (P<i>_filR1-filR2</i>) were amplified from the anti-FilR1 antibody immunoprecipitated DNA (Ab_FilR1), and input DNA sample before immunoprecipitation (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095502#s4" target="_blank">Material and Methods</a>) as a positive control (Input). Almost no PCR products were amplified from the mock-IP DNA (CK) samples. (B) qPCR detected the enrichment folds of the DNA fragments in anti-FilR1 antibody immunoprecipitated DNA (Ab_FilR1, gray bar) over mock-IP control (CK, black bar). PCR amplifications were performed using the specific primers for the promoter regions of <i>filR1</i> (P<i>_filR1</i>) and <i>filI-filR2</i> operon (P<i>_filI-R2</i>). An intragenic DNA fragment of the16S rRNA gene (16 s) was included as the negative control.</p

There were different level of Cav-1 expression in all five HCC cell lines and forced expression of Cav-1 leaded to up-regulation of cell migration and invasion and EMT phenotype of Huh7 cells.

<p>(A) The Cav-1 expression was different in five kinds of HCC cell lines; (B) Cav-1 expression in Huh7 cells was confirmed to be increased significantly after transfected with Cav-1 expressing plasmid by both qRT-PCR and Western immunoblotting; (C) As assessed by the wound healing assay, cell migration rate was increased in Huh7 cells by enforced expression of Cav-1 at both 24 and 48hours; (D) As assessed by Millicell invasion chamber assay, invasion capacity of Huh7 cells was increased apparently after overexpression of Cav-1; (E) After overexpression of Cav-1, E-cadherin expression was repressed and expression of mesenchymal markers including N-cadherin, Fibronectin and Vimentin was enhanced clearly.</p

Expression of the archaeal promoters in the <i>E. coli ex vivo</i> reporter system.

a.<p>Values are shown as relative light units and the average of at least three independent readings.</p>b.<p>Genes and operons shown in each reporter plasmid are listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095502#pone.0095502.s004" target="_blank">Table S1</a>.</p>c.<p>Fold difference of the luciferase activity are calculated from those determined for <i>E. coli</i> strain carrying plasmid pairs of FilR1-vacant p184 plus pO^x-lux over that of the strain carrying pOx-lux alone (+p184/−), strain with FilR1 plus pO^x-lux over that with pO^x-lux alone (+pFilR1/−), and strain with FilR1 plus pO^x-lux over that with FilR1-vacant p184 plus pO^x-lux (+pFilR1/+p184).</p

Schematic representation of the domain structures of FilI and FilR proteins.

<p>(A) Domain structure of FilI analyzed using programs of Pfam and NCBI blast. (B) Location analysis of domains in FilI through the programs of TMHMM, TMpred and SOSUI. (C) Domain structures of FilR1 and FilR2 were analyzed by programs of Pfam and NCBI blast. In addition, the amino acid identity (%) for the aligned fragments of FilR1 and FilR2 is shown on the right. (D) Protein sequence alignment of the REC domains of FilR1 (C-terminal 276–446aa) and FilR2 (the whole length) by software GeneDoc. Identical amino acids are shown with a black background, while similar amino acids are shown with a gray background.</p