Microporous Metal–Organic Framework Based on a Bifunctional Linker for Selective Sorption of CO₂ over N₂ and CH₄

A bifunctional organic linker 4-(4-carboxyphenyl)-1,2,4-triazole (HCPT), incorporating both carboxylate and triazole groups, has been successfully used in the construction of a 2-fold interpenetrated dynamic metal–organic framework (MOF), {[Cu₃(CPT)₄(μ₃-OH)]·NO₃·7H₂O·EtOH}<i>_n</i> (<b>1</b>) based on a triangular Cu­(II)-hydroxo cluster as secondary building unit (SBU). Upon solvation/desolvation and temperature, the crystal cell parameters of <b>1</b> could be fine-tuned. More importantly, a transformation from disordered phase to a more ordered phase after activation was observed via a single-crystal-to-single-crystal mode. Gas sorption studies reveal that the activated <b>1</b> exhibits highly selective sorption of CO₂ over N₂ and CH₄ at room temperature

Microporous Metal–Organic Framework Based on a Bifunctional Linker for Selective Sorption of CO₂ over N₂ and CH₄

A bifunctional organic linker 4-(4-carboxyphenyl)-1,2,4-triazole (HCPT), incorporating both carboxylate and triazole groups, has been successfully used in the construction of a 2-fold interpenetrated dynamic metal–organic framework (MOF), {[Cu₃(CPT)₄(μ₃-OH)]·NO₃·7H₂O·EtOH}<i>_n</i> (<b>1</b>) based on a triangular Cu­(II)-hydroxo cluster as secondary building unit (SBU). Upon solvation/desolvation and temperature, the crystal cell parameters of <b>1</b> could be fine-tuned. More importantly, a transformation from disordered phase to a more ordered phase after activation was observed via a single-crystal-to-single-crystal mode. Gas sorption studies reveal that the activated <b>1</b> exhibits highly selective sorption of CO₂ over N₂ and CH₄ at room temperature

A Family of Binuclear Dysprosium(III) Radical Compounds with Magnetic Relaxation in ON and OFF States

Four binuclear dysprosium compounds incorporating the radical ligand 2-(4-oxidopyridyl)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide (PyNONIT) have been successfully synthesized under appropriate conditions. Centrosymmetric bimetallic Dy₂O₂ cores in all of the compounds through double-μ₂-oxygen atoms of the <i>N</i>-oxide groups are realized in a metal–radical approach for the first time. Dimers <b>1</b> and <b>2</b>, of the same formula {[Dy­(hfac)₃(PyNONIT)]₂}₂ (hfac = hexafluoroacetylacetonate) but obtained by different methods, which contain almost identical local symmetry of <i>D</i>_4<i>d</i> and Dy–(O)₂–Dy bridging fashion, however, display no out-of-phase alternating-current (ac) signal for <b>1</b> and slow relaxation of the magnetization for <b>2</b> corresponding to the difference of the crystal packing mode. The adduct ([Dy­(hfac)₃(PyNONIT)]₂[Dy_0.5(hfac)_1.5(H₂O)]₂) (<b>3</b>) consists of two items, the dimer [Dy­(hfac)₃(PyNONIT)]₂ and the monomer [Dy­(hfac)₃(H₂O)₂], where the symmetry of Dy^III ion in Dy₂O₂ decreases to <i>D</i>_2<i>d</i>, showing slow relaxation of the magnetization at lower temperature. Interestingly, a moisture-mediated reversible solid transformation between <b>1</b> and ([Dy­(hfac)₃(H₂O)­(PyNONIT)]₂) (<b>4</b>) has been investigated. Spongelike <b>1</b> can undergo a transition from eight to nine coordination at room temperature through hydration. A different coordination field is mostly responsible for no ac signal noticed for <b>4</b>. The structural diversity of the Dy₂ family provides an opportunity to expand the investigation on 4f single-molecule magnets. Approaches that the relaxation of the supramolecular dimer can be tuned to ON and OFF states modulated by the packing mode and ligand field are presented

A Family of Binuclear Dysprosium(III) Radical Compounds with Magnetic Relaxation in ON and OFF States

Four binuclear dysprosium compounds incorporating the radical ligand 2-(4-oxidopyridyl)-4,4,5,5-tetramethylimidazolin-1-oxyl-3-oxide (PyNONIT) have been successfully synthesized under appropriate conditions. Centrosymmetric bimetallic Dy₂O₂ cores in all of the compounds through double-μ₂-oxygen atoms of the <i>N</i>-oxide groups are realized in a metal–radical approach for the first time. Dimers <b>1</b> and <b>2</b>, of the same formula {[Dy­(hfac)₃(PyNONIT)]₂}₂ (hfac = hexafluoroacetylacetonate) but obtained by different methods, which contain almost identical local symmetry of <i>D</i>_4<i>d</i> and Dy–(O)₂–Dy bridging fashion, however, display no out-of-phase alternating-current (ac) signal for <b>1</b> and slow relaxation of the magnetization for <b>2</b> corresponding to the difference of the crystal packing mode. The adduct ([Dy­(hfac)₃(PyNONIT)]₂[Dy_0.5(hfac)_1.5(H₂O)]₂) (<b>3</b>) consists of two items, the dimer [Dy­(hfac)₃(PyNONIT)]₂ and the monomer [Dy­(hfac)₃(H₂O)₂], where the symmetry of Dy^III ion in Dy₂O₂ decreases to <i>D</i>_2<i>d</i>, showing slow relaxation of the magnetization at lower temperature. Interestingly, a moisture-mediated reversible solid transformation between <b>1</b> and ([Dy­(hfac)₃(H₂O)­(PyNONIT)]₂) (<b>4</b>) has been investigated. Spongelike <b>1</b> can undergo a transition from eight to nine coordination at room temperature through hydration. A different coordination field is mostly responsible for no ac signal noticed for <b>4</b>. The structural diversity of the Dy₂ family provides an opportunity to expand the investigation on 4f single-molecule magnets. Approaches that the relaxation of the supramolecular dimer can be tuned to ON and OFF states modulated by the packing mode and ligand field are presented

Rad54-2A exhibits a dsDNA binding defect.

<p><b>A</b>. Rad54 (left panel) and Rad54-2A (right panel) were incubated with pUC19 supercoiled dsDNA at the indicated stoichiometries (bp DNA:Rad54 monomer) in the absence of nucleotide cofactor (upper panels), in the presence of 5 mM ATP and an ATP-regeneraton system (middle panels) or in the presence of 5 mM ATP-γ-S (lower panels) at 30°C for 15 minutes. The DNA-protein complexes were fixed by glutaraldehyde (GA) and visualized on a 1% agarose gel. <b>B</b>. Quantification of the DNA protein complexes from <i>A</i>.</p

Rad54-2A is defective in D-loop extension catalyzed by Klenow polymerase.

<p><b>A</b>. Reaction scheme of <i>in vitro</i> reconstitution system for Rad54-supported D-loop formation and D-loop extension by Klenow DNA polymerase. <b>B</b>. D-loop formation and extension by Klenow (lanes 1–10) in the presence of Rad54 (lanes 1–5) and Rad54-2A (lanes 6–10), respectively. <b>C</b>. Quantification of reactions in <i>B</i> for total D-loops at 0 min DNA polymerase extension time. <b>D.</b> Quantification of D-loop extension as a function of time.</p

A Conserved Sequence Extending Motif III of the Motor Domain in the Snf2-Family DNA Translocase Rad54 Is Critical for ATPase Activity

<div><p>Rad54 is a dsDNA-dependent ATPase that translocates on duplex DNA. Its ATPase function is essential for homologous recombination, a pathway critical for meiotic chromosome segregation, repair of complex DNA damage, and recovery of stalled or broken replication forks. In recombination, Rad54 cooperates with Rad51 protein and is required to dissociate Rad51 from heteroduplex DNA to allow access by DNA polymerases for recombination-associated DNA synthesis. Sequence analysis revealed that Rad54 contains a perfect match to the consensus PIP box sequence, a widely spread PCNA interaction motif. Indeed, Rad54 interacts directly with PCNA, but this interaction is not mediated by the Rad54 PIP box-like sequence. This sequence is located as an extension of motif III of the Rad54 motor domain and is essential for full Rad54 ATPase activity. Mutations in this motif render Rad54 non-functional <i>in vivo</i> and severely compromise its activities <i>in vitro</i>. Further analysis demonstrated that such mutations affect dsDNA binding, consistent with the location of this sequence motif on the surface of the cleft formed by two RecA-like domains, which likely forms the dsDNA binding site of Rad54. Our study identified a novel sequence motif critical for Rad54 function and showed that even perfect matches to the PIP box consensus may not necessarily identify PCNA interaction sites.</p></div

Rad54-2A is deficient in D-loop formation in reconstituted D-loop reactions containing PCNA.

<p><b>A</b>, Reaction scheme of <i>in vitro</i> reconstitution system for Rad54-supported D-loop formation and D-loop extension by DNA polymerase δ. <b>B.</b> Analysis of D-loop formation and extension products in reactions with Rad54 (lanes 1–8) and Rad54-2A (lanes 9–16) by 1% native agarose gel electrophoresis in the presence of PCNA and RFC (lanes 1–4 and 9–12) or in the absence of PCNA (lanes 5–8 and 13–16). <b>C</b>. Quantification of reactions in <i>B</i> for total D-loops at 0 min DNA polymerase extension time. <b>D.</b> Quantification of D-loop extension as a function of time.</p

<i>In vitro</i> interaction between Rad54 and PCNA.

<p><b>A.</b> Bacterial cell extracts and purified PCNA used in the GST pulldown assay. Lane 1, size markers; lane 2, 5 µg BL21(DE3) cell extract (Control CE); lane 3, 5 µg cell extract from BL21(DE3) overexpressing yeast PCNA (PCNA CE). PCNA was expressed significantly without IPTG induction. Lane 4 contains 2 µg GST-affinity purified PCNA. Left panel, Coomassie stained SDS-PAGE gel; right panel, immunoblots with anti-yeast PCNA anti-serum. <b>B.</b> Rad54 and PCNA (purified or in cell extract) interaction demonstrated by GST pulldown assays. Lane 1, size markers; lane 2, PCNA loading control (2 µg); lane 3–6, GST pulldown control; lane 7–10, GST-Rad54 pulldown assay. <b>C.</b> The Rad54-PCNA interaction does not depend on the canonical PIP box sequence. The interaction of GST-Rad54 and GST-Rad54-Y494A-F495A (GST-Rad54-2A) with purified PCNA and PCNA from cell extract was detected with GST pulldown assay visualized by both Coomassie (upper panel) and immunoblotting with yeast PCNA anti-serum (lower panel). Left panel, GST pulldown with cell extracts. Right panel, GST pulldown with PCNA cell extract (PCNA CE, 10 µg) and purified PCNA (2 µg). Lane 1 & 11, size markers; lane 2–4 & 12–14 were from GST (2 µg) pulldown control; lanes 5–7 & 15–17 were from GST-Rad54 (2 µg) pulldown, lanes 8–10 & 18–20 were from GST-Rad54-2A (2 µg) pulldown. Molecular weight markers are given in kDa.</p

Rad54-2A is not functional <i>in vivo</i> and is expressed at normal protein levels.

<p><b>A.</b>. <i>rad54-2A</i> cells are extremely MMS-sensitive. Cell cultures of wild type (WDHY2217), <i>rad54-Y494A, F495A ( = rad54-2A</i>, WDHY2625), and <i>rad54-Δ</i> (WDHY2571) were grown in YPD, diluted to OD₆₀₀ of 1, followed by 6 five-fold serial dilutions. Cells were plated onto YPD containing 0.0025% or 0.01% MMS and grown at 30°C for 2 days and images were acquired to document cell growth. <b>B.</b> Comparison of endogenous wild type Rad54 and Rad54-2A protein levels. Extracts (100 µg) from wild type (WDHY2217), <i>rad54-2A</i> (WDHY2625) and <i>rad54-Δ</i> (WDHY2571) cells were immunoblotted with anti-<i>S. cerevisiae</i> Rad54 serum. The Rad54 protein levels were quantified using a crossreacting band as loading control. The ratios of the intensity of Rad54/control are indicated.</p