Thermal annealing of iridescent cellulose nanocrystal films.

The properties of chiral nematic and iridescent cellulose nanocrystal films with different monovalent cations (CNC-X) obtained through evaporation-induced self-assembly (EISA) can be modified by a variety of external stimuli. Here, we study the transformations of their optical and structural properties when the films are thermally annealed at 200 °C and 240 °C for up to 2 days. The chiral nematic structure of the most thermally stable films is not destroyed even after extensive heating due to the thermochemical stability of the cellulose backbone and the presence of surface alkali counterions, which suppress catalysis of early stage degradation. Despite the resilience of the cholesteric structure and the overall integrity of heated CNC-X films, thermal annealing is often accompanied by reduction of iridescence, birefringence, and transparency, as well as formation of degradation products. The versatility, sustainability, and stability of CNC-X films highlight their potential as temperature indicators and photonic devices.

Field-stepwise-swept QCPMG solid-state 115In NMR of indium oxide.

Experimental and theoretical investigations of indium-115 electric-field-gradient (EFG) tensors of indium(III) oxide, In2O3, have been presented. Field-stepwise-swept QCPMG solid-state 115In NMR experiments are carried out at T â€‹= â€‹120 â€‹K, observed at 52.695 â€‹MHz, and in the range of external magnetic fields between 4.0 and 6.5 â€‹T. The spectral simulations yield the quadrupolar coupling constant, CQ value, of 183(2) MHz and the asymmetry parameter, ηQ, of 0.05(5), for In(1), and that of 126(2) MHz and ηQ of 0.86(5) for In(2). Quantum chemical calculations are carried out to provide 115In EFG tensor orientations with respect to the molecular structure. A relationship between operative frequencies and variable ranges of external magnetic fields is briefly discussed for field-swept solid-state 115In NMR.

Solid-state 23Na NMR spectroscopy studies of ordered and disordered cellulose nanocrystal films.

Cellulose nanocrystal films with either disordered or chiral nematic structures of varying helical pitch were investigated using 23Na solid-state nuclear magnetic resonance (NMR) spectroscopy. Spin lattice relaxation of 1H correlated with 23Na analyzed by indirect observation using polarization transfer from 1H nuclei to 23Na nuclei showed that the Na+ cations are well hydrated in the cellulose nanocrystal films. Linewidth analysis in solid-state 23Na NMR showed that the Na+ cations move in confined spaces, and that the Na+ cations in the film having disordered structure are more dynamic than in the films having ordered structure. From lineshape analysis of the 23Na 2D nutation NMR spectra, we can distinguish the Na+ environments within the ordered and disordered films, and find trends in anisotropic interaction parameters between ordered samples with different pitches. These are the first detailed 23Na NMR spectroscopic studies of CNC-Na+ films, and they show that this technique may be a powerful probe for characterizing the extent of order in nanocellulose samples.

Investigation of the effects of sintering and indium-doping of zinc oxide using 67Zn magic angle spinning NMR analysis.

Indium-doped zinc oxide, a potential alternative material to indium tin oxide, was analyzed in powder form via 67Zn magic angle spinning nuclear magnetic resonance (MAS NMR). The 67Zn MAS NMR results show that the line shapes of zinc oxide were broadened by sintering, which was also observed for indium-doped zinc oxide, in which the broadening also depended on the sintering time. Furthermore, the line shapes of indium-doped zinc oxide were significantly broader than those of the corresponding zinc oxide, and were independent of the degree of indium doping. This indicates that indium atoms are associated into cluster-like structures in this compound.

An NMR study on the mechanisms of freezing and melting of water confined in spherically mesoporous silicas SBA-16.

Thermodynamic and dynamic properties of water confined in mesoporous silica glass SBA-16 were investigated by DSC, and (1,2)H NMR spectroscopy and (2)H NMR spin-lattice relaxation time (T1) as a function of pore size. SBA-16 possesses the main spherical pores, interconnecting channels and micropores (corona). Water in the characteristic spherical pores of SBA-16 freezes at the homogeneous nucleation temperature of water. Between room and freezing temperatures, the correlation time of the isotropic rotation of water in the pores of SBA-16 followed the Vogel-Fulcher-Tammann (VFT) relation, which reflects the formation and growth of clusters of fragile water for changing to the strong water. The vitrification of water in micropores around 200 K was observed by (2)H NMR. Above 200 K, the correlation time of the rotation of water in micropores exhibited non-Arrhenius behavior, which is correlated with the gradual decrease in the mobility of water due to the growth of hydrogen bonding, forming low density water before vitrification. After vitrification, the activation energy of the rotation of water in micropores was 25-33 kJ mol(-1), which was similar to that in ice Ih for all samples. The freedom of cluster formation and water rotation increased with the increasing the pore size.

Identification of physiological and toxic conformations in Abeta42 aggregates.

Aggregation of the 42-residue amyloid beta-protein (Abeta42) plays a crucial role in the pathogenesis of Alzheimer's disease (AD). Despite numerous structural studies on Abeta aggregates, the relationship between tertiary structure and toxicity remains unclear. Our proline scanning and solid-state NMR studies suggested that aggregates both of wild-type Abeta42 and of E22K-Abeta42 (one of the mutants related to cerebral amyloid angiopathy) contain two conformers: a major one with a turn at positions 25 and 26, and a minor one with a turn at positions 22 and 23. To identify the toxic conformer, the derivative Abeta42-lactam(22K-23E), in which the side chains at positions 22 and 23 were covalently linked, was synthesized as a minor conformer surrogate, along with Abeta42-lactam(25K-26E) as a major conformer surrogate. The Abeta42-lactam(22K-23E) showed stronger aggregation, neurotoxicity, radical generation, and oligomerization than wild-type Abeta42, whereas in Abeta42-lactam(25K-26E) were weak. The transition from the physiological conformation with a turn at positions 25 and 26 to the toxic conformation with a turn at positions 22 and 23 might be a key event in the pathogenesis of AD.

Verification of the intermolecular parallel beta-sheet in E22K-Abeta42 aggregates by solid-state NMR using rotational resonance: implications for the supramolecular arrangement of the toxic conformer of Abeta42.

Formation of the intermolecular beta-sheet is a key event in the aggregation of 42-residue amyloid-beta (Abeta42). We have recently identified a physiological and toxic conformer, the turn positions of which are slightly different from each other, in the aggregates of E22K-Abeta42 (one of the mutants related to cerebral amyloid angiopathy). However, it remains unclear whether the intermolecular beta-sheet in the E22K-Abeta42 aggregates is parallel or antiparallel. We prepared an equal mixture of E22K-Abeta42 aggregates labeled at C(alpha) and those labeled at C=O with (13)C, whose intermolecular (13)C-(13)C distance was estimated by solid-state NMR using rotational resonance (R2). The intermolecular proximity of beta-strands at positions 21 and 30 was less than 6 A, supporting the existence of the intermolecular parallel beta-sheet in the E22K-Abeta42 aggregates as well as in wild-type Abeta42 aggregates. The results also suggest that each conformer would not accumulate alternately, but form a relatively large assembly.

Verification of the C-terminal intramolecular beta-sheet in Abeta42 aggregates using solid-state NMR: implications for potent neurotoxicity through the formation of radicals.

Structural analysis of 42-residue amyloid beta (Abeta42) aggregates using rotational resonance in solid-state NMR verified that C(beta) and/or C(gamma) of Met-35 and the carboxyl carbon of Ala-42 are proximal enough to form an intramolecular antiparallel beta-sheet in the C-terminus. The S-oxidized radical cation at Met-35, an ultimate radical species responsible for neurotoxicity, could be stabilized by the carboxylate anion at the C-terminus, resulting in aggregation to cause long-term oxidative stress.

Asymmetric (13)C-(13)C polarization transfer under dipolar-assisted rotational resonance in magic-angle spinning NMR.

A two-dimensional (2D) homonuclear exchange NMR spectrum in solids often shows an asymmetric cross-peak pattern, which disturbs a quantitative analysis of peak intensities. When magnetization is prepared using cross polarization (CP), the asymmetry can naively be ascribed to nonequilibrium initial magnetization. We show, however, that the CP effect cannot fully explain the observed mixing-time dependence of the peak intensities in 2D (13)C-(13)C exchange spectra of [2,3-(13)C] l-alanine (2,3-Ala) under (13)C-(1)H dipolar-assisted rotational resonance (DARR) recoupling, which has recently been proposed for a broadband recoupling method under magic-angle spinning. We develop a theory to describe polarization transfer in a two-spin system under DARR recoupling. By taking into account the effects of the partial spectral overlap among (13)C signals, which is a unique feature of DARR recoupling, and (1)H-(1)H flip-flop exchange, we can successfully explain the observed mixing-time dependence of the peak intensities of 2D (13)C-(13)C DARR exchange spectra of 2,3-Ala. A simple initial-rate analysis is also examined.

Structure of beta-amyloid fibrils and its relevance to their neurotoxicity: implications for the pathogenesis of Alzheimer's disease.

Alzheimer's disease and cerebral amyloid angiopathy are characterized by the deposition of beta-amyloid fibrils consisting of 40- and 42-mer peptides (A beta 40 and A beta 42). Since the aggregation (fibrilization) of these peptides is closely related to the pathogenesis of these diseases, numerous structural analyses of A beta 40 and A beta 42 fibrils have been carried out. A beta 42 plays a more important role in the pathogenesis of these diseases since its aggregative ability and neurotoxicity are considerably greater than those of A beta 40. This review summarizes mainly our own recent findings from the structural analysis of A beta 42 fibrils and discusses its relevance to their neurotoxicity in vitro.

Verification of the turn at positions 22 and 23 of the beta-amyloid fibrils with Italian mutation using solid-state NMR.

The aggregation of 42-mer amyloid beta (Abeta42) plays a central role in the pathogenesis of Alzheimer's disease. Our recent research on proline mutagenesis of Abeta42 suggested that the formation of a turn structure at positions 22 and 23 could play a crucial role in its aggregative ability and neurotoxicity. Since E22K-Abeta42 (Italian mutation) aggregated more rapidly and with more potent neurotoxicity than wild-type Abeta42, the tertiary structure at positions 21-24 of E22K-Abeta42 fibrils was analyzed by solid-state NMR using dipolar-assisted rotational resonance (DARR) to identify the 'malignant' conformation of Abeta42. Two sets of chemical shifts for Asp-23 were observed in a ratio of about 2.6:1. The 2D DARR spectra at the mixing time of 500 ms suggested that the side chains of Asp-23 and Val-24 in the major conformer, and those of Lys-22 and Asp-23 in the minor conformer could be located on the same side, respectively. These data support the presence of a turn structure at positions 22 and 23 in E22K-Abeta42 fibrils. The formation of a salt bridge between Lys-22 and Asp-23 in the minor conformer might be a reason why E22K-Abeta42 is more pathogenic than wild-type Abeta42.