Intermolecular Interactions and Aggregation of <i>fac</i>-Tris(2-phenylpyridinato‑<i>C</i>²,<i>N</i>)iridium(III) in Nonpolar Solvents

The intermolecular interaction and aggregation of the neutral complex <i>fac</i>-tris­(2-phenylpyridinato-<i>C</i>²,<i>N</i>)­iridium­(III) (<i>fac</i>-Ir­(ppy)₃) in solution was investigated. Intermolecular interactions were found to effectively decrease the luminescence lifetime via self-quenching with increasing <i>fac</i>-Ir­(ppy)₃ concentrations. A Stern–Volmer plot for quenching in acetonitrile was linear, due to bimolecular self-quenching, but curved in toluene as the result of excimer formation. ¹H NMR spectra demonstrated a monomer–aggregate equilibrium which resulted in spectral shifts depending on solvent polarity. X-ray crystallography provided structural information concerning the aggregate, which is based on a tetramer consisting of two Δ-<i>fac</i>-Ir­(ppy)₃–Λ-<i>fac</i>-Ir­(ppy)₃ pairs. Offset π–π stacking of ppy ligands and electrostatic dipole–dipole interactions between complex molecules play an important role in the formation of these molecular pairs

Four-Electron Oxidative Dehydrogenation Induced by Proton-Coupled Electron Transfer in Ruthenium(III) Complex with 2‑(1,4,5,6-Tetrahydropyrimidin-2-yl)phenolate

New ruthenium­(II or III) complexes with general formula [Ru­(O-N)­(bpy)₂]^<i>n</i>+ (O-N = unsymmetrical bidentate phenolate ligand; bpy = 2,2′-bipyridine) were synthesized, and their crystal structures and electrochemical properties were characterized. Ru^II complexes with 2-(2-imidazolinyl)­phenolate (Himn^–) or 2-(1,4,5,6-tetrahydropyrimidin-2-yl)­phenolate (Hthp^–) could be deprotonated by addition of excess KO^<i>t</i>Bu, although the deprotonated species were easily reprotonated by exposure to air. Unlike these Ru^II complexes, their Ru^III analogs showed interesting ligand oxidation reactions upon addition of bases. With [Ru^III(Himn)­(bpy)₂]²⁺, two-electron oxidation of Himn^– and reduction of the Ru^III center resulted in conversion of the 2-imidazolinyl group to a 2-imidazolyl group. On the other hand, the corresponding Hthp^– complex exhibited four-electron oxidation of the ligand to form 2-(2-pyrimidyl)­phenolate (pym^–). These aromatization reactions of imidazolinyl and 1,4,5,6-tetrahydropyrimidyl groups were also achieved by the electrochemically generated Ru^III complexes

Intermolecular Interactions and Aggregation of <i>fac</i>-Tris(2-phenylpyridinato‑<i>C</i>²,<i>N</i>)iridium(III) in Nonpolar Solvents

The intermolecular interaction and aggregation of the neutral complex <i>fac</i>-tris­(2-phenylpyridinato-<i>C</i>²,<i>N</i>)­iridium­(III) (<i>fac</i>-Ir­(ppy)₃) in solution was investigated. Intermolecular interactions were found to effectively decrease the luminescence lifetime via self-quenching with increasing <i>fac</i>-Ir­(ppy)₃ concentrations. A Stern–Volmer plot for quenching in acetonitrile was linear, due to bimolecular self-quenching, but curved in toluene as the result of excimer formation. ¹H NMR spectra demonstrated a monomer–aggregate equilibrium which resulted in spectral shifts depending on solvent polarity. X-ray crystallography provided structural information concerning the aggregate, which is based on a tetramer consisting of two Δ-<i>fac</i>-Ir­(ppy)₃–Λ-<i>fac</i>-Ir­(ppy)₃ pairs. Offset π–π stacking of ppy ligands and electrostatic dipole–dipole interactions between complex molecules play an important role in the formation of these molecular pairs

Four-Electron Oxidative Dehydrogenation Induced by Proton-Coupled Electron Transfer in Ruthenium(III) Complex with 2‑(1,4,5,6-Tetrahydropyrimidin-2-yl)phenolate

New ruthenium­(II or III) complexes with general formula [Ru­(O-N)­(bpy)₂]^<i>n</i>+ (O-N = unsymmetrical bidentate phenolate ligand; bpy = 2,2′-bipyridine) were synthesized, and their crystal structures and electrochemical properties were characterized. Ru^II complexes with 2-(2-imidazolinyl)­phenolate (Himn^–) or 2-(1,4,5,6-tetrahydropyrimidin-2-yl)­phenolate (Hthp^–) could be deprotonated by addition of excess KO^<i>t</i>Bu, although the deprotonated species were easily reprotonated by exposure to air. Unlike these Ru^II complexes, their Ru^III analogs showed interesting ligand oxidation reactions upon addition of bases. With [Ru^III(Himn)­(bpy)₂]²⁺, two-electron oxidation of Himn^– and reduction of the Ru^III center resulted in conversion of the 2-imidazolinyl group to a 2-imidazolyl group. On the other hand, the corresponding Hthp^– complex exhibited four-electron oxidation of the ligand to form 2-(2-pyrimidyl)­phenolate (pym^–). These aromatization reactions of imidazolinyl and 1,4,5,6-tetrahydropyrimidyl groups were also achieved by the electrochemically generated Ru^III complexes

Differential Effect of HDAC3 on Cytoplasmic and Nuclear Huntingtin Aggregates

<div><p>Histone deacetylases (HDACs) are potential therapeutic targets of polyglutamine (pQ) diseases including Huntington’s disease (HD) that may function to correct aberrant transcriptional deactivation caused by mutant pQ proteins. HDAC3 is a unique class 1 HDAC found in both the cytoplasm and in the nucleus. However, the precise functions of HDAC3 in the two cellular compartments are only vaguely known. HDAC3 directly binds to huntingtin (Htt) with short pQ and this interaction is important for suppressing neurotoxicity induced by HDAC3. With long pQ Htt, the interaction with HDAC3 is inhibited, and this supposedly promotes neuronal death, indicating that HDAC3 would be a good therapeutic target for HD. However, the knockout of one HDAC3 allele did not show any efficacy in reducing neurodegenerative symptoms in a mouse model of HD. Therefore, the role of HDAC3 in the pathogenesis of HD has yet to be fully elucidated. We attempted to resolve this issue by focusing on the different roles of HDAC3 on cytoplasmic and nuclear Htt aggregates. In addition to supporting the previous findings, we found that HDAC3 preferentially binds to nuclear Htt over cytoplasmic ones. Specific HDAC3 inhibitors increased the total amount of Htt aggregates by increasing the amount of nuclear aggregates. Both cytoplasmic and nuclear Htt aggregates were able to suppress endogenous HDAC3 activity, which led to decreased nuclear proteasome activity. Therefore, we concluded that Htt aggregates impair nuclear proteasome activity through the inhibition of HDAC3. Our findings provide new insights regarding cross-compartment proteasome regulation.</p></div

MOESM1 of Effective cleaning of rust stained marble

Additional file 1: Fig S1. ATR-FTIR spectrum of the white precipitate. The ATR-FTIR spectrum of the white precipitate identifies it as cystine

Effect of HDAC3 on cytoplasmic and nuclear Htt aggregates.

<p><b>A:</b> Aspartate at the 166^th and 168^th amino acid of HDAC3 is crucial for its activity. An empty plasmid (–), FLAG tagged wild-type (wt), or D166A + D168A mutant (DA) of HDAC3 were overexpressed in 293T cells. After immunoprecipitation using anti-FLAG antibodies, pan-histone deacetylase activity was measured by fluorometric analysis. *P≤0.05 vs. empty plasmid by ANOVA and multiple comparisons. N = 3. Anti-FLAG and anti-actin western blots from cell lysates are shown below. <b>B–C:</b> HDAC3 overexpression reduces nuclear Htt-ex1 aggregates. Empty vector (–), FLAG-tagged wild-type or DA mutant HDAC3 were transfected to E3 and N3 cells. Amount of aggregate measured by filter trap assay are shown in B and C. *significant against – and DA by ANOVA and multiple comparisons. N = 3. <b>D–G</b>: Empty vector (–), FLAG-tagged wild-type or DA mutant HDAC3 were transfected to E3 and N3 cells. Cells harboring inclusion bodies are counted and their fraction in total cells was plotted in 2D and E. Representative GFP images of low powered magnification fields are shown in 2F and 2G. *significant against – and DA by ANOVA and multiple comparisons. <b>H:</b> HDAC3 shRNA reduces HDAC3 amount by 70%. Molecular weight markers are shown at the left side. <b>I–J:</b> HDAC3 knockdown increases nuclear aggregates. HDAC3 shRNA was transfected into E3 or N3 cells and the 1% TritonX-100 insoluble fraction was subjected to filter trap assay. *P = 0.0003 by <i>t</i>-test. N = 3.</p

HDAC3 preferably binds to nuclear Htt with long Qs.

<p><b>A:</b> GST-HDAC3 binds directly to either cytoplasmic or nuclear Htt-ex1. GST pull-down assay of E1, E2, E3 (cytoplasm), and N1, N2, N3 (nuclear) HeLa cell lysates is shown. Pulled-down fraction was analyzed by anti-GFP or GST antibodies. *Non-specific band. <b>B:</b> HDAC3 immunoprecipitates almost exclusively with nuclear Htt-ex1s. E1, E3 (cytoplasm), N1, and N3 (nuclear) HeLa cells were transfected with FLAG-tagged HDAC3 and those lysates were immunoprecipitated with anti-FLAG antibodies immobilized to protein G agarose beads. The pre-IP fraction and the IPed fraction were analyzed using anti-FLAG or anti-GFP antibodies. Molecular weight markers are shown on the left. <b>C:</b> HDAC3 associates exclusively with nuclear inclusion bodies. E3 or N3 cells were fixed and stained with anti-HDAC3 antibodies and visualized by Alexa 546 conjugated secondary antibodies. Arrowheads: inclusion bodies with no HDAC3 signals associated. Arrows: HDAC3 signal-associated inclusion bodies. Bar = 20 µm.</p

Hydrogen-Bonded Supramolecular Structures of Cobalt(III) Complexes with Unsymmetrical Bidentate Ligands: <i>mer</i>/<i>fac</i> Interconversion Induced by Hydrogen-Bonding Interactions

Cobalt­(III) complexes with three unsymmetrical bidentate ligands containing a noncoordinating N–H bond and a phenolate-<i>O</i> donor as hydrogen-bond donor and acceptor, respectively, were prepared and characterized. ¹H NMR spectroscopy indicated that all the tris-chelate Co­(III) complexes prepared favor the <i>mer</i> configuration in solution. [Co­(Hthp)₃] and [Co­(Himn)₃] also possess the <i>mer</i> configuration in the crystals (Hthp^– = 2-(1,4,5,6-tetrahydropyrimidin-2-yl)­phenolate, Himn^– = 2-(2-imidazolinyl)­phenolate). On the other hand, [Co­(Himl)₃] takes the <i>fac</i> configuration in the crystal (Himl^– = 2-(2-imidazolyl)­phenolate). These Co­(III) complexes showed three types of characteristic supramolecular structures: ladder, distorted hexagonal sheet, and honeycomb sheet structure, constructed by intermolecular hydrogen bonds. Heating [Co­(Himn)₃] and [Co­(Himl)₃] in methanol selectively afforded precipitates of the <i>fac</i> isomer due to the low solubility of the hydrogen-bonded supramolecular structures. This <i>mer</i> to <i>fac</i> isomerization upon crystallization in methanol is presumably induced by the formation of highly ordered hydrogen-bond networks via the methanol molecule. The <i>fac</i> isomers remained intact in dimethyl sulfoxide (DMSO) for longer than a week at room temperature. Upon heating, however, <i>fac</i> to <i>mer</i> geometrical isomerization of both <i>fac</i>-[Co­(Himn)₃] and <i>fac</i>-[Co­(Himl)₃] was observed in DMSO. Thus, <i>mer</i>/<i>fac</i> interconversion was achieved by heating in two different solvents, due to the formation of a supramolecular assembly of hydrogen-bond networks

HDAC3 inhibitors have differential effects on cytoplasmic and nuclear Htt-ex1 aggregates.

<p><b>A:</b> HDAC3 inhibitors increase aggregated nuclear Htt-ex1. For filter trap analysis, three independently made insoluble fractions were analyzed on one single membrane; thus, there are error bars shown for 0×IC50s. *P≤0.05, ***P≤0.001 vs. each 0×IC50 by ANOVA and multiple comparisons. N = 3. <b>B:</b> HDAC3 inhibitors reduce cytoplasmic soluble Htt-ex1s. The effect of various HDAC inhibitors on 1% TritonX-100 soluble cytoplasmic Htt-ex1s. Indicated amount of HDAC inhibitors were added to E3 (cytoplasmic) or N3 (nuclear) cells for 48 h. Quantitated band intensity was normalized to each band without HDAC inhibitors (0×IC50); thus, there are no error bars. **P≤0.01, ***P≤0.001 vs. each 0×IC50 by ANOVA with multiple comparisons. N = 3. Anti-actin blots are shown for loading control.</p