Unexpected Nonresponsive Behavior of a Flexible Metal-Organic Framework under Conformational Changes of a Photoresponsive Guest Molecule

In this article, we describe the synthesis, characterization, and optical properties of a photochromic-guest-incorporated metal-organic framework (MOF). The photochromic guest molecule, 2-phenylazopyridine (PAP), was introduced into a pre-synthesized porous crystalline host MOF, [Zn₂(1,4-bdc)₂(dabco)]<i>_n</i> (<b>1</b>). The successful embedment of PAP has been confirmed by elemental analysis, powder X-ray diffraction measurements, IR spectroscopy, etc. The number of PAP molecules per unit cell of host was 1.0, as evidenced by elemental and thermogravimetric analyses of the host–guest composite, <b>1⊃PAP</b>. The <b>1⊃PAP</b> composite did not adsorb N₂, revealed by the adsorption isotherm of <b>1⊃PAP</b>, which indicates the pore blockage by the close contact of the host framework with the guest PAP in the trans form. The light-induced trans/cis isomerization with partial reversibility of the guest molecule (PAP) in this hybrid host–guest compound (<b>1⊃PAP</b>) has been investigated by detailed IR spectroscopy and UV–vis spectroscopy. The structural transformation from tetragonal in <b>1</b> to orthorhombic in <b>1⊃PAP</b> exhibits dynamic nature of the framework upon inclusion of guest in the framework, which remarkably becomes nonresponsive with the photoirradiation of guest PAP, retaining its orthorhombic structure in the photoirradiated complex, <b>1⊃PAP­(UV)</b>

Palladium(II) Complexes of the First Pincer (Se,N,Se) Ligand, 2,6-Bis((phenylseleno)methyl)pyridine (L): Solvent-Dependent Formation of [PdCl(L)]Cl and Na[PdCl(L)][PdCl₄] and High Catalytic Activity for the Heck Reaction

The reaction of PhSe− with 2,6-bis(chloromethyl)pyridine has resulted in the first pincer (Se,N,Se) ligand, 2,6-bis((phenylseleno)methyl)pyridine (L), which has formed two types of complexes, [PdCl(L)]Cl (1) and Na[PdCl(L)][PdCl4](2), when reacted with Na2[PdCl4], depending upon the solvent. The complex 2 is formed in methanolic medium and 1 in an acetone−water (2:1) mixture. L, 1, and 2 have been characterized by proton, carbon-13, and selenium-77 NMR spectra and single-crystal X-ray crystallography. The Pd−Se bond length is between 2.3891(1) and 2.4313(7) Å due to the trans influence of two Se donor atoms on each other and the rigidity of L. The noncovalent interactions (hydrogen bonding) present in the crystal of 1 make a ring structure comprising its six molecules. In the case of complex 2, a dimeric unit is formed due to such interactions. The geometry around Pd is nearly square planar for both the complexes. 1 and 2 are both efficient as catalysts for the Heck coupling (C−C) reaction, as the yield and TON values are up to 97% and 97 000, respectively. For complex 2 yields and TON values are higher in comparison to those obtained with 1

Palladium(II) Complexes of the First Pincer (Se,N,Se) Ligand, 2,6-Bis((phenylseleno)methyl)pyridine (L): Solvent-Dependent Formation of [PdCl(L)]Cl and Na[PdCl(L)][PdCl₄] and High Catalytic Activity for the Heck Reaction

The reaction of PhSe− with 2,6-bis(chloromethyl)pyridine has resulted in the first pincer (Se,N,Se) ligand, 2,6-bis((phenylseleno)methyl)pyridine (L), which has formed two types of complexes, [PdCl(L)]Cl (1) and Na[PdCl(L)][PdCl4](2), when reacted with Na2[PdCl4], depending upon the solvent. The complex 2 is formed in methanolic medium and 1 in an acetone−water (2:1) mixture. L, 1, and 2 have been characterized by proton, carbon-13, and selenium-77 NMR spectra and single-crystal X-ray crystallography. The Pd−Se bond length is between 2.3891(1) and 2.4313(7) Å due to the trans influence of two Se donor atoms on each other and the rigidity of L. The noncovalent interactions (hydrogen bonding) present in the crystal of 1 make a ring structure comprising its six molecules. In the case of complex 2, a dimeric unit is formed due to such interactions. The geometry around Pd is nearly square planar for both the complexes. 1 and 2 are both efficient as catalysts for the Heck coupling (C−C) reaction, as the yield and TON values are up to 97% and 97 000, respectively. For complex 2 yields and TON values are higher in comparison to those obtained with 1

Sensitive Valence Structures of [(pap)₂Ru(Q)]^<i>n</i> (<i>n</i> = +2, +1, 0, −1, −2) with Two Different Redox Noninnocent Ligands, Q = 3,5-Di-<i>tert</i>-butyl-<i>N</i>-aryl-1,2-benzoquinonemonoimine and pap = 2-Phenylazopyridine

The complexes [(pap)2Ru(Q)]ClO4, [1]ClO4−[4]ClO4, with two different redox noninnocent ligands, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine (-aryl = m-(Cl)2C6H3 (1+), C6H5 (2+), m-(OCH3)2C6H3 (3+), and m-(tBu)2C6H3 (4+)) and pap = 2-phenylazopyridine, have been synthesized and characterized using various analytical techniques. The single-crystal X-ray structure of the representative [2]ClO4·C7H8 exhibits multiple intermolecular C−H···O hydrogen bondings and C−H···π interactions. The C1−O1 = 1.287(4) (density functional theory, DFT, 1.311) and C6−N1 = 1.320(4) (DFT, 1.353) Å and intraring bond distances associated with the sensitive quinine (Q) moiety along with the azo(pap) bond distances, N3−N4 = 1.278(4) (DFT, 1.297) and N6−N7 = 1.271(4) (DFT, 1.289) Å, in 2+ justify the [(pap)2RuII(Q•−)]+ valence configuration at the native state of 1+−4+. Consequently, Mulliken spin densities on Q, pap, and Ru in 2+ are calculated to be 0.8636, 0.1040, and 0.0187, respectively, and 1+−4+ exhibit free radical sharp EPR spectra and one weak and broad transition around 1000 nm in CH3CN due to interligand transition involving a singly occupied molecular orbital (SOMO) of Q•− and the vacant π* orbital of pap. Compounds 1+−4+ undergo a quasi-reversible oxidation and three successive reductions. The valence structure of the electron paramagnetic resonance (EPR)-inactive oxidized state in 12+−42+ has been established as [(pap)2RuII(Q°)]2+ instead of the alternate formalism of antiferromagnetically coupled [(pap)2RuIII(Q•−)]2+ on the basis of the DFT calculations on the optimized 2+, which predict that the singly occupied molecular orbital is primarily composed of Q with 77% contribution. Accordingly, the optimized structure of 22+ predicts shorter C1−O1 (1.264) and C6−N1 (1.317 Å) distances and longer Ru1−O1 (2.080) and Ru1−N1 (2.088 Å) distances. Compounds 12+−42+ exhibit the lowest energy transitions around 600 nm, corresponding to Ru(dπ)/Q(π) → pap(π*). The presence of two sets of strongly π-acceptor ligands, pap and Q, in 12+−42+ stabilizes the Ru(II) state to a large extent such that the further oxidation of {RuII−Q°} → {RuIII−Q°} has not been detected within +2.0 V versus a saturated calomel electrode. The EPR-inactive reduced states 1−4 have been formulated as [(pap)2RuII(Q2−)] over the antiferromagnetically coupled alternate configuration, [(pap)(pap•−)RuII(Q•−)]. The optimized structure of 2 predicts sensitive C1−O1 and C6−N1 bond distances of 1.337 and 1.390 Å, respectively, close to the doubly reduced Q2− state, whereas the NN distances of pap, N3−N4 = 1.299 and N6−N7 = 1.306 Å, remain close to the neutral state. In corroboration with the doubly reduced Q2− state, 1−4 exhibit a moderately strong interligand π(Q2−) → π*(pap) transition in the near-IR region near 1300 nm. The subsequent two reductions are naturally centered around the azo functions of the pap ligands

DataSheet1_An interplay between BRD4 and G9a regulates skeletal myogenesis.docx

Histone acetylation and methylation are epigenetic modifications that are dynamically regulated by chromatin modifiers to precisely regulate gene expression. However, the interplay by which histone modifications are synchronized to coordinate cellular differentiation is not fully understood. In this study, we demonstrate a relationship between BRD4, a reader of acetylation marks, and G9a, a writer of methylation marks in the regulation of myogenic differentiation. Using loss- and gain-of-function studies, as well as a pharmacological inhibition of its activity, we examined the mechanism by which BRD4 regulates myogenesis. Transcriptomic analysis using RNA sequencing revealed that a number of myogenic differentiation genes are downregulated in Brd4-depleted cells. Interestingly, some of these genes were upregulated upon G9a knockdown, indicating that BRD4 and G9a play opposing roles in the control of myogenic gene expression. Remarkably, the differentiation defect caused by Brd4 knockdown was rescued by inhibition of G9a methyltransferase activity. These findings demonstrate that the absence of BRD4 results in the upregulation of G9a activity and consequently impaired myogenic differentiation. Collectively, our study identifies an interdependence between BRD4 and G9a for the precise control of transcriptional outputs to regulate myogenesis.</p

Temperature-Independent Catalytic Two-Electron Reduction of Dioxygen by Ferrocenes with a Copper(II) Tris[2-(2-pyridyl)ethyl]amine Catalyst in the Presence of Perchloric Acid

Selective two-electron plus two-proton (2e^–/2H⁺) reduction of O₂ to hydrogen peroxide by ferrocene (Fc) or 1,1′-dimethylferrocene (Me₂Fc) in the presence of perchloric acid is catalyzed efficiently by a mononuclear copper­(II) complex, [Cu^II(tepa)]²⁺ (<b>1</b>; tepa = tris­[2-(2-pyridyl)­ethyl]­amine) in acetone. The <i>E</i>_1/2 value for [Cu^II(tepa)]²⁺ as measured by cyclic voltammetry is 0.07 V vs Fc/Fc⁺ in acetone, being significantly positive, which makes it possible to use relatively weak one-electron reductants such as Fc and Me₂Fc for the overall two-electron reduction of O₂. Fast electron transfer from Fc or Me₂Fc to <b>1</b> affords the corresponding Cu^I complex [Cu^I(tepa)]⁺ (<b>2</b>), which reacts at low temperature (193 K) with O₂, however only in the presence of HClO₄, to afford the hydroperoxo complex [Cu^II(tepa)­(OOH)]⁺ (<b>3</b>). A detailed kinetic study on the homogeneous catalytic system reveals the rate-determining step to be the O₂-binding process in the presence of HClO₄ at lower temperature as well as at room temperature. The O₂-binding kinetics in the presence of HClO₄ were studied, demonstrating that the rate of formation of the hydroperoxo complex <b>3</b> as well as the overall catalytic reaction remained virtually the same with changing temperature. The apparent lack of activation energy for the catalytic two-electron reduction of O₂ is shown to result from the existence of a pre-equilibrium between <b>2</b> and O₂ prior to the formation of the hydroperoxo complex <b>3</b>. No further reduction of [Cu^II(tepa)­(OOH)]⁺ (<b>3</b>) by Fc or Me₂Fc occurred, and instead <b>3</b> is protonated by HClO₄ to yield H₂O₂ accompanied by regeneration of <b>1</b>, thus completing the catalytic cycle for the two-electron reduction of O₂ by Fc or Me₂Fc

Acid-Induced Mechanism Change and Overpotential Decrease in Dioxygen Reduction Catalysis with a Dinuclear Copper Complex

Catalytic four-electron reduction of O₂ by ferrocene (Fc) and 1,1′-dimethylferrocene (Me₂Fc) occurs efficiently with a dinuclear copper­(II) complex [Cu^II₂(XYLO)­(OH)]²⁺ (<b>1</b>), where XYLO is a <i>m</i>-xylene-linked bis­[(2-(2-pyridyl)­ethyl)­amine] dinucleating ligand with copper-bridging phenolate moiety], in the presence of perchloric acid (HClO₄) in acetone at 298 K. The hydroxide and phenoxo group in [Cu^II₂(XYLO)­(OH)]²⁺ (<b>1</b>) undergo protonation with HClO₄ to produce [Cu^II₂(XYLOH)]⁴⁺ (<b>2</b>) where the two copper centers become independent and the reduction potential shifts from −0.68 V vs SCE in the absence of HClO₄ to 0.47 V; this makes possible the use of relatively weak one-electron reductants such as Fc and Me₂Fc, significantly reducing the effective overpotential in the catalytic O₂-reduction reaction. The mechanism of the reaction has been clarified on the basis of kinetic studies on the overall catalytic reaction as well as each step in the catalytic cycle and also by low-temperature detection of intermediates. The O₂-binding to the fully reduced complex [Cu^I₂(XYLOH)]²⁺ (<b>3</b>) results in the reversible formation of the hydroperoxo complex ([Cu^II₂(XYLO)­(OOH)]²⁺) (<b>4</b>), followed by proton-coupled electron-transfer (PCET) reduction to complete the overall O₂-to-2H₂O catalytic conversion

Oxidation State Analysis of a Four-Component Redox Series [Os(pap)₂(Q)]^<i>n</i> Involving Two Different Non-Innocent Ligands on a Redox-Active Transition Metal

Complexes [Os(pap)2(Q)] (1–4) have been obtained and structurally characterized for pap = 2-phenylazopyridine and Q = 4,6-di-tert-butyl-N-aryl-o-iminobenzoquinone (aryl = phenyl (1), 3,5-dichlorophenyl (2), 3,5-dimethoxyphenyl (3), or 3,5-di-tert-butylphenyl (4)). The oxidized form (3)(ClO4)2 was also crystallographically characterized while the odd-electron intermediates [Os(pap)2(Q)]+ (1+–4+) and [Os(pap)2(Q)]− (2–) were investigated by electron paramagnetic resonance (EPR) and UV–vis–NIR spectroelectrochemistry in conjunction with density functional theory (DFT) spin density and time-dependent DFT (TD-DFT) calculations. The results from the structural, spectroscopic, and electrochemical experiments and from the computational studies allow for the assignments [OsII(pap0)2(Q0)]2+, [OsII(pap0)2(Q•–)]+, [OsIV(pap•–)2(Q2–)], and [OsII(pap•–)(pap0)(Q2–)]−, with comproportionation constants Kc ≈ 103.5, 1010, 1018, and 105, respectively. The redox potentials and the comproportionation constants exhibit similarities and differences between Ru and Os analogues. While the Q-based redox reactions show identical potentials, the more metal-involving processes exhibit cathodic shifts for the osmium systems, leading to distinctly different comproportionation constants for some intermediates, especially to a stabilization of the neutral osmium compounds described in this article. The example [Os(pap)2(Q)]n illustrates especially the power of combined structural and EPR analysis with support from DFT towards the valence state description of transition metal complexes incorporating redox non-innocent ligands

Oxidation State Analysis of a Four-Component Redox Series [Os(pap)₂(Q)]^<i>n</i> Involving Two Different Non-Innocent Ligands on a Redox-Active Transition Metal

Complexes [Os(pap)2(Q)] (1–4) have been obtained and structurally characterized for pap = 2-phenylazopyridine and Q = 4,6-di-tert-butyl-N-aryl-o-iminobenzoquinone (aryl = phenyl (1), 3,5-dichlorophenyl (2), 3,5-dimethoxyphenyl (3), or 3,5-di-tert-butylphenyl (4)). The oxidized form (3)(ClO4)2 was also crystallographically characterized while the odd-electron intermediates [Os(pap)2(Q)]+ (1+–4+) and [Os(pap)2(Q)]− (2–) were investigated by electron paramagnetic resonance (EPR) and UV–vis–NIR spectroelectrochemistry in conjunction with density functional theory (DFT) spin density and time-dependent DFT (TD-DFT) calculations. The results from the structural, spectroscopic, and electrochemical experiments and from the computational studies allow for the assignments [OsII(pap0)2(Q0)]2+, [OsII(pap0)2(Q•–)]+, [OsIV(pap•–)2(Q2–)], and [OsII(pap•–)(pap0)(Q2–)]−, with comproportionation constants Kc ≈ 103.5, 1010, 1018, and 105, respectively. The redox potentials and the comproportionation constants exhibit similarities and differences between Ru and Os analogues. While the Q-based redox reactions show identical potentials, the more metal-involving processes exhibit cathodic shifts for the osmium systems, leading to distinctly different comproportionation constants for some intermediates, especially to a stabilization of the neutral osmium compounds described in this article. The example [Os(pap)2(Q)]n illustrates especially the power of combined structural and EPR analysis with support from DFT towards the valence state description of transition metal complexes incorporating redox non-innocent ligands