Solid-state NMR ¹³C homonuclear through-space correlation spectra of [U⁻¹³C, ¹⁵N] Aβ(1–40) bound to DMPC MLVs acquired by DARR/RAD with mixing times of (A) 10 ms and (B) 100 ms, respectively.

<p>All measurements were performed at 20°C for the sample (DMPC/Aβ(1–40) molar ratio = 10/1) in lyophilized and dry state.</p

Solid-state NMR correlation spectra of [U-¹³C, ¹⁵N] Aβ(1–40) bound to DMPC bilayers for signal assignments.

<p>(A) ¹³C-CTUC-COSY homonuclear correlation spectrum. (B) NCO and (C) NCA heteronuclear correlation spectra based on DCP. All measurements were performed at 20°C for the sample (DMPC/Aβ(1–40) molar ratio = 10/1) in lyophilized and dry state.</p

Structural model of Aβ(1–40) bound to DMPC bilayers characterized by solid-state NMR analyses together with amino acid sequence of Aβ(1–40).

<p>Structural model of Aβ(1–40) bound to DMPC bilayers characterized by solid-state NMR analyses together with amino acid sequence of Aβ(1–40).</p

Formal Aryne/Carbon Monoxide Copolymerization To Form Aromatic Polyketones/Polyketals

A palladium-catalyzed alternating copolymerization of [2.2.1]­oxabicyclic alkenes <b>1</b> with carbon monoxide afforded isomer mixtures of polyketones <b>2</b>_<b>ktn</b> and polyketals <b>2</b>_<b>ktl</b>. Subsequent acid-induced dehydration of polymer <b>2</b> furnished novel aromatic polymers consisting of polyketones <b>3</b>_<b>ktn</b> and polyketals <b>3</b>_<b>ktl</b> units. This formal aryne/carbon monoxide copolymerization thus generated the first example of poly­(aryne-<i>alt</i>-carbon monoxide)­s, in which <i>o</i>-arylene and carbonyl units are incorporated in an alternating fashion

Electron Localization of Polyoxomolybdates with ε‑Keggin Structure Studied by Solid-State ⁹⁵Mo NMR and DFT Calculation

We report electron localization of polyoxomolybdates with ε-Keggin structure investigated by solid-state ⁹⁵Mo NMR and DFT calculation. The polyoxomolybdates studied are the basic ε-Keggin crystals of [Me₃NH]₆[H₂Mo₁₂O₂₈(OH)₁₂{MoO₃}₄]·2H₂O (<b>1</b>), the crystals suggested to have a disordered {ε-Mo₁₂} core of [PMo₁₂O₃₆(OH)₄{La­(H₂O)_2.75Cl_1.25}₄]·27H₂O (<b>2</b>), and the paramagnetic Keggin crystals of [H₂Mo₁₂O₃₀(OH)₁₀{Ni­(H₂O)₃}₄]·14H₂O (<b>3</b>). The spectra of ⁹⁵Mo static NMR of these samples were measured under moderate (9.4 and 11.7 T) and ultrahigh magnetic fields (21.8 T). From spectral simulation and quantum chemical calculation, the NMR parameters of the chemical shift and quadrupole interactions for ⁹⁵Mo were estimated. By the analysis based on the result for <b>1</b>, it was found for <b>2</b> that although the {ε-Mo₁₂} core is disordered, the eight d¹ electrons in it are not completely localized on four Mo–Mo bonds. Furthermore, it was shown for <b>3</b> that the d¹ electrons are localized to make the Mo–Mo bonds, while the unpaired electrons are also almost localized on the paramagnetic Ni^II ions

Quantitative Analysis of Solid-State Homonuclear Correlation Spectra of Antiparallel β‑Sheet Alanine Tetramers

Poly-l-alanine (PLA) sequences are a key element in the structure of the crystalline domains of spider dragline silks, wild silkworm silks, antifreeze proteins, and amyloids. To date, no atomic-level structures of antiparallel (AP)-PLA longer than Ala₄ have been reported using the single-crystal X-ray diffraction analysis. In this work, dipolar-assisted rotational resonance solid-state NMR spectra were observed to determine the effective internuclear distances of ¹³C uniformly labeled alanine tetramer with antiparallel (AP) β-sheet structure whose atomic coordinates are determined from the X-ray crystallographic analysis. Initial build-up rates, <i>R</i>_{<i>j</i>,<i>k</i>}, were obtained from the build-up curves of the cross peaks by considering the internuclear distances arising in the master equation. Subsequently, experimentally obtained effective internuclear distances, <i>r</i>^eff_{<i>j</i>,<i>k</i>}(obs), were compared with the calculated <i>r</i>^eff_{<i>j</i>,<i>k</i>}(calc) values obtained from the X-ray crystallographic data. Fairly good correlation between <i>r</i>^eff_{<i>j</i>,<i>k</i>}(obs) and <i>r</i>^eff_{<i>j</i>,<i>k</i>}(calc) was obtained in the range of 1.0–6.0 Å, with the standard deviation of 0.244 Å, without considering the zero-quantum line-shape functions. It was further noted that the internuclear distances of intermolecular contributions provide details relating to the molecular packing in solid-state samples. Thus, the present data agree well with AP-β-sheet packing but do not agree with P-β-sheet packing

Determination of Accurate ¹H Positions of (Ala-Gly)n as a Sequential Peptide Model of Bombyx mori Silk Fibroin before Spinning (Silk I)

The accurate ¹H positions of alanine-glycine alternating copolypeptide, (AG)₁₅ with Silk I structure were determined. For the purpose, the geometry optimization was performed starting with the atomic coordinates of the hetero atoms reported previously (Macromolecules 2005, 38, 7397−7403) and applied only for protons under periodic boundary conditions. The agreement between the calculated and observed chemical shifts of all ¹H,¹³C and ¹⁵N nuclei was excellent, indicating strongly that the determination of all the atomic-coordinate including ¹H nuclei was performed with high accuracy. Here the ¹H chemical shift was obtained by using both 1 mm microcoil MAS NMR probe-head for mass-limited solid-state samples developed by us and ultrahigh field NMR at 920 MHz. The DQ correlations in the ¹H DQMAS NMR spectra were also used to confirm the intra- and intermolecular structures obtained here. The characteristic structure of Silk I which can be easily converted to Silk II by external forces was discussed together with the generation of Silk I structure from the aqueous solution of the silk fibroin