Beta Amyloid Oligomers with Higher Cytotoxicity have Higher Sidechain Dynamics.

The underlying biophysical principle governing the cytotoxicity of the oligomeric aggregates of ß-amyloid (Aß) peptides has long been an enigma. Here we show that the size of Aß40 oligomers can be actively controlled by incubating the peptides in reverse micelles. Our approach allowed for the first time a detailed comparison of the structures and dynamics of two Aß40 oligomers of different sizes, viz., 10 and 23 nm, by solid-state NMR. From the chemical shift data, we infer that the conformation and/or the chemical environments of the residues from K16 to K28 are different between the 10-nm and 23-nm oligomers. We find that the 10-nm oligomers are more cytotoxic, and the molecular motion of the sidechain of its charged residue K16 is more dynamic. Interestingly, the residue A21 exhibits unusually high structural rigidity. Our data raise an interesting possibility that the cytotoxicity of Aß40 oligomers could also be correlated to the motional dynamics of the sidechains.

Uncovering the Role of Bicarbonate in Calcium Carbonate Formation at Near-Neutral pH.

Mechanistic pathways relevant to mineralization are not well-understood fundamentally, let alone in the context of their biological and geological environments. Through quantitative analysis of ion association at near-neutral pH, we identify the involvement of HCO3- ions in CaCO3 nucleation. Incorporation of HCO3- ions into the structure of amorphous intermediates is corroborated by solid-state nuclear magnetic resonance spectroscopy, complemented by quantum mechanical calculations and molecular dynamics simulations. We identify the roles of HCO3- ions as being through (i) competition for ion association during the formation of ion pairs and ion clusters prior to nucleation and (ii) incorporation as a significant structural component of amorphous mineral particles. The roles of HCO3- ions as active soluble species and structural constituents in CaCO3 formation are of fundamental importance and provide a basis for a better understanding of physiological and geological mineralization.

Materials Engineering of Violin Soundboards by Stradivari and Guarneri.

We investigated the material properties of Cremonese soundboards using a wide range of spectroscopic, microscopic, and chemical techniques. We found similar types of spruce in Cremonese soundboards as in modern instruments, but Cremonese spruces exhibit unnatural elemental compositions and oxidation patterns that suggest artificial manipulation. Combining analytical data and historical information, we may deduce the minerals being added and their potential functions-borax and metal sulfates for fungal suppression, table salt for moisture control, alum for molecular crosslinking, and potash or quicklime for alkaline treatment. The overall purpose may have been wood preservation or acoustic tuning. Hemicellulose fragmentation and altered cellulose nanostructures are observed in heavily treated Stradivari specimens, which show diminished second-harmonic generation signals. Guarneri's practice of crosslinking wood fibers via aluminum coordination may also affect mechanical and acoustic properties. Our data suggest that old masters undertook materials engineering experiments to produce soundboards with unique properties.

Chemical distinctions between Stradivari's maple and modern tonewood.

Violins made by Antonio Stradivari are renowned for having been the preferred instruments of many leading violinists for over two centuries. There have been long-standing questions about whether wood used by Stradivari possessed unique properties compared with modern tonewood for violin making. Analyses of maple samples removed from four Stradivari and a Guarneri instrument revealed highly distinct organic and inorganic compositions compared with modern maples. By solid-state 13C NMR spectroscopy, we observed that about one-third of hemicellulose had decomposed after three centuries, accompanied by signs of lignin oxidation. No apparent changes in cellulose were detected by NMR and synchrotron X-ray diffraction. By thermogravimetric analysis, historical maples exhibited reduced equilibrium moisture content. In differential scanning calorimetry measurements, only maples from Stradivari violins, but not his cellos, exhibited unusual thermooxidation patterns distinct from natural wood. Elemental analyses by inductively coupled plasma mass spectrometry suggested that Stradivari's maples were treated with complex mineral preservatives containing Al, Ca, Cu, Na, K, and Zn. This type of chemical seasoning was an unusual practice, unknown to later generations of violin makers. In their current state, maples in Stradivari violins have very different chemical properties compared with their modern counterparts, likely due to the combined effects of aging, chemical treatments, and vibrations. These findings may inspire further chemical experimentation with tonewood processing for instrument making in the 21st century.

Characterization of Phosphorus Species in Human Dentin by Solid-State NMR.

The rat has been considered as an appropriate animal model for the study of the mineralization process in humans. In this work, we found that the phosphorus species in human dentin characterized by solid-state NMR spectroscopy consist mainly of orthophosphate and hydrogen phosphate. Some orthophosphates are found in a disordered phase, where the phosphate ions are hydrogen-bonded to structural water, some present a stoichiometric apatite structure, and some a hydroxyl-depleted apatite structure. The results of this study are largely the same as those previously obtained for rat dentin. However, the relative amounts of the various phosphorus species in human and rat dentin are dramatically different. In particular, stoichiometric apatite is more abundant in human dentin than in rat dentin, whereas the converse is true for disordered-phase orthophosphates. Furthermore, spatial proximity among all phosphorus species in human dentin is identical within experimental error, in contrast to what observed for rat dentin. Although it is not clear how these spectroscopic data could relate to the hierarchical structure or the mechanical properties of teeth, our data reveal that the molecular structures of human and rat dentin at different growth stages are not exactly the same.

Fibrillization of ß-Amyloid Peptides via Chemically Modulated Pathway.

The aggregation of ß-amyloid peptides is closely associated with Alzheimer's disease. We have used liposomes to modulate the early aggregation events of 40-residue ß-amyloid peptides. The spatial confinement provided by liposomes leads to the formation of nonfibrillar aggregates of ß-amyloid peptides. These on-pathway ß-sheet intermediates were used to seed the fibrillization of the monomer peptides. Solid-state NMR spectroscopy revealed that the resultant fibrils have a more uniform structure than those formed in liposome-free solution.

High-Magnesium Calcite Mesocrystals: Formation in Aqueous Solution under Ambient Conditions.

Mesocrystals of high-magnesian calcites are commonly found in biogenic calcites. Under ambient conditions, it remains challenging to prepare mesocrystals of high-magnesian calcite in aqueous solution. We report that mesocrystals of calcite with magnesium content of about 20 mol % can be obtained from the phase transformation of magnesian amorphous calcium carbonate (Mg-ACC) in lipid solution. The limited water content on the Mg-ACC surface would reduce the extent of the dissolution-reprecipitation process and bias the phase transformation pathway toward solid-state reaction. We infer from the selected area electron diffraction patterns and the dark-field transmission electron microscopic images that the formation of Mg-calcite mesocrystals occurs through solid-state secondary nucleation, for which the phase transformation is initiated near the mineral surface and the crystalline phase propagates gradually toward the interior part of the microspheres of Mg-ACC.

Probing the spatial organization of bacteriochlorophyll C by solid-state nuclear magnetic resonance.

Green sulfur bacteria, which live in extremely low-light environments, use chlorosomes to harvest light. A chlorosome is the most efficient, and arguably the simplest, light-harvesting antenna complex, which contains hundreds of thousands of densely packed bacteriochlorophylls (BChls). To harvest light efficiently, BChls in a chlorosome form supramolecular aggregates; thus, it is of great interest to determine the organization of the BChls in a chlorosome. In this study, we conducted a (13)C solid-state nuclear magnetic resonance and Mg K-edge X-ray absorption analysis of chlorosomes from wild-type Chlorobaculum tepidum. The X-ray absorption results indicated that the coordination number of the Mg in the chlorosome must be >4, providing evidence that electrostatic interactions formed between the Mg of a BChl and the carbonyl group or the hydroxyl group of the neighboring BChl molecule. According to the intermolecular distance constraints obtained on the basis of (13)C homonuclear dipolar correlation spectroscopy, we determined that the molecular assembly of BChls is dimer-based and that the hydrogen bonds among the BChls are less extensive than commonly presumed because of the twist in the orientation of the BChl dimers. This paper also reports the first (13)C homonuclear correlation spectrum acquired for carotenoids and lipids-which are minor, but crucial, components of chlorosomes-extracted from wild-type Cba. tepidum.

Purification of recombinant nacre-associated mineralization protein AP7 fused with maltose-binding protein.

Formation of biominerals often involves specific proteins that modulate the process of matrix assembly, nucleation, and crystal growth. AP7 is an aragonite-associated protein of 7 kDa and is intrinsically disordered. The structural disorder of AP7 makes it very difficult to express in Escherchiacoli. In this work, we report the first successful expression and purification of recombinant AP7 using the maltose-binding protein (MBP) fusion approach. We obtain a high-yield production of recombinant MBP-AP7 protein inE. coli (∼60 mg/L). We also establish an efficient protocol to remove the MBP fusion protein by Factor Xa, followed by purification using size-exclusion chromatography. Characterization of the recombinant AP7 protein has been carried out using MALDI-TOF, peptide mass fingerprinting, and circular dichroism (CD). The mass data confirm that the purified recombinant protein is AP7. The CD data suggest that the recombinant AP7 protein exists as partially disordered structure at neutral pH. The calcium carbonate precipitation assay shows that both MBP-AP7 and AP7 exhibit morphological modification on calcite crystallites. The co-precipitation of MBP-tagged AP7 derivatives and calcium carbonate generate different types of AP7 composite calcite and vaterite crystals. This system should be helpful to establish a model for understanding the structure/function relationship between the protein and inorganic mineral interaction.

Wood cellulose microfibrils have a 24-chain core-shell nanostructure in seed plants.

Wood cellulose microfibril (CMF) is the most abundant organic substance on Earth but its nanostructure remains poorly understood. There are controversies regarding the glucan chain number (N) of CMFs during initial synthesis and whether they become fused afterward. Here, we combined small-angle X-ray scattering, solid-state nuclear magnetic resonance and X-ray diffraction analyses to resolve CMF nanostructures in native wood. We developed small-angle X-ray scattering measurement methods for the cross-section aspect ratio and area of the crystalline-ordered CMF core, which has a higher scattering length density than the semidisordered shell zone. The 1:1 aspect ratio suggested that CMFs remain mostly segregated, not fused. The area measurement reflected the chain number in the core zone (Ncore). To measure the ratio of ordered cellulose over total cellulose (Roc) by solid-state nuclear magnetic resonance, we developed a method termed global iterative fitting of T1ρ-edited decay (GIFTED), in addition to the conventional proton spin relaxation editing method. Using the formula N = Ncore/Roc, most wood CMFs were found to contain 24 glucan chains, conserved between gymnosperm and angiosperm trees. The average CMF has a crystalline-ordered core of ~2.2 nm diameter and a semidisordered shell of ~0.5 nm thickness. In naturally and artificially aged wood, we observed only CMF aggregation (contact without crystalline continuity) but not fusion (forming a conjoined crystalline unit). This further argued against the existence of partially fused CMFs in new wood, overturning the recently proposed 18-chain fusion hypothesis. Our findings are important for advancing wood structural knowledge and more efficient use of wood resources in sustainable bio-economies.

Hydrogen phosphates play a critical structural role in amorphous calcium phosphates.

Amorphous calcium phosphate (ACP) is an intriguing mineral phase of calcium phosphate in its own right, in addition to its relevance in biomineralization. We hereby demonstrate that ACPs prepared by different synthetic routes such as the crosslinking of inorganic oligomers and polymer-induced liquid precursors have distinctive relative compositions of orthophosphate and hydrogen phosphate, and the extent of their hydrogen bonding with water. For all the ACPs or ACP-derived materials studied in this work, the species of hydrogen phosphate is the most important structural element. Depending on the synthetic pathways, orthophosphate and water, as well as their associated hydrogen bonds, may also play a role in the structural formation of ACPs.

Site specific NMR characterization of abeta-40 oligomers cross seeded by abeta-42 oligomers.

Extracellular accumulation of ß amyloid peptides of 40 (Aß40) and 42 residues (Aß42) has been considered as one of the hallmarks in the pathology of Alzheimer's disease. In this work, we are able to prepare oligomeric aggregates of Aß with uniform size and monomorphic structure. Our experimental design is to incubate Aß peptides in reverse micelles (RMs) so that the peptides could aggregate only through a single nucleation process and the size of the oligomers is confined by the physical dimension of the reverse micelles. The hence obtained Aß oligomers (AßOs) are 23 nm in diameter and they belong to the category of high molecular-weight (MW) oligomers. The solid-state NMR data revealed that Aß40Os adopt the structural motif of ß-loop-ß but the chemical shifts manifested that they may be structurally different from low-MW AßOs and mature fibrils. From the thioflavin-T results, we found that high-MW Aß42Os can accelerate the fibrillization of Aß40 monomers. Our protocol allows performing cross-seeding experiments among oligomeric species. By comparing the chemical shifts of Aß40Os cross seeded by Aß42Os and those of Aß40Os prepared in the absence of Aß42Os, we observed that the chemical states of E11, K16, and E22 were altered, whereas the backbone conformation of the ß-sheet region near the C-terminus was structurally invariant. The use of reverse micelles allows hitherto the most detailed characterization of the structural variability of Aß40Os.

Faster magic angle spinning reveals cellulose conformations in woods.

We present a first report on the detection of three different C6 conformers of cellulose in spruce, as revealed by solid-state 1H-13C correlation spectra. The breakthrough in 1H resolution is achieved by magic-angle spinning in the regime of 150 kHz. The suppression of dense dipolar network of 1H provides inverse detected 13C spectra at a good sensitivity even in natural samples. We find that the glycosidic linkages are initially more ordered in spruce than maple, but a thermal treatment of spruce leads to a more heterogeneous packing order of the remaining cellulose fibrils.

Formation and Near-Infrared Emission of CsPbI3 Nanoparticles Embedded in Cs4PbI6 Crystals.

Cs4PbI6, as a rarely investigated member of the Cs4PbX6 (X is a halogen element) family, has been successfully synthesized at low temperatures, and the synthetic conditions have been optimized. Metal iodides such as LiI, KI, NiI2, CoI2, and ZnI2, as additives, play an important role in enhancing the formation of the Cs4PbI6 microcrystals. ZnI2 with the lowest dissociation energy is the most efficient additive to supply iodide ions, and its amount of addition has also been optimized. Strong red to near-infrared (NIR) emission properties have been detected, and its optical emission centers have been identified to be numerous embedded perovskite-type α-CsPbI3 nanocrystallites (∼5 nm in diameter) based on investigations of temperature- and pressure-dependent photoluminescent properties. High-resolution transmission electron microscopy was used to detect these hidden nanoparticles, although the material was highly beam-sensitive and confirmed a "raisin bread"-like structure of the Cs4PbI6 crystals. A NIR mini-LED for the biological application has been successfully fabricated using as-synthesized Cs4PbI6 crystals. This work provides information for the future development of infrared fluorescent nanoscale perovskite materials.

Formation of nano-magnesite in the calcareous spicules prepared under ambient conditions.

We report that high-Mg calcite spherulites can undergo a coarsening process to form calcareous spicules of ∼30 microns in width and several hundred microns in length after an aging process in air for a prolonged period. During the aging process, the crystallinity of the calcitic structure has been improved substantially with a significant migration of Mg ions toward the mineral surface. In a thin-foil sample of the spicule aged for 20 months, nanocrystallites of magnesite with minor substitution level of Ca ions have been found near the surface of the spicule.

Manifold of self-assembly of a de novo designed peptide: amyloid fibrils, peptide bundles, and fractals.

We report that a peptide with the sequence of EGAGAAAAGAGE can have different aggregation states, viz., amyloid fibrils, peptide bundles, and fractal assembly under different incubation conditions. The chemical state of the Glu residue played a pivotal regulating role in the aggregation behavior of the peptide. The mechanism of the fractal assembly of this peptide has been unraveled as follows. The peptide fragments adopting the beta-sheet conformation are well dispersed in alkaline solution. In the buffer of sodium bicarbonate, peptide rods are formed with considerable structural rigidity at the C- and N-termini. The peptide rods undergo random trajectory in the solution and form a fractal pattern on a two-dimensional surface via the diffusion-limited aggregation process.

Anhydrous amorphous calcium carbonate (ACC) is structurally different from the transient phase of biogenic ACC.

Amorphous calcium carbonate (ACC) is an important precursor phase of biogenic calcite. In this work, an in situ Ca L-edge X-ray absorption spectroscopic study has been carried out to monitor the phase transformation process of hydrated ACC from room temperature to 773 K in the presence of water vapor pressure at 0.4 mbar. The L2,3 crystal field splittings of the near edge X-ray absorption fine structure (NEXAFS) spectra acquired for hydrated and anhydrous ACC are indistinguishable. The transformation process from anhydrous ACC to calcite is greatly facilitated by the presence of water moisture. Our data acquired for nano-calcite are in close resemblance to those reported for "type 2" ACC in sea urchin larval spicules. We suggest that "type 2 ACC" or the "transient phase of ACC" is a disordered calcium carbonate phase with a nascent calcitic structure at the nanometer length scale.

Preparation and Structural Characterization of Free-Standing Octacalcium-Phosphate-Rich Thin Films.

Free-standing films of calcium phosphates exhibit many favorable properties for tissue engineering. In this work, a thin film of calcium phosphate is prepared in a liposome suspension using the method of ammonia gas diffusion. The thickness of the film is about 10 µm, and the lateral dimensions are on the length scale of millimeter. The results of powder X-ray diffraction and transmission electron microscopy show that the thin films contain the mineral phases of hydroxyapatite and octacalcium phosphate (OCP). Using solid-state NMR spectroscopy, in particular the technique of heteronuclear correlation spectroscopy with variable contact time, the major crystalline phase of the thin film has been confirmed to be OCP.

Preparation of fibril nuclei of beta-amyloid peptides in reverse micelles.

We report the preparation of protofibrils from oligomeric Aß40 aggregates, which have been incubated under spatially constrained conditions. The molecular structure of the resultant protofibrils is highly homogeneous, suggesting that the phenomenon of structural polymorphism commonly observed in Aß40 fibrils may be largely due to multiple nucleation events.

A novel sol-gel-derived calcium silicate cement with short setting time for application in endodontic repair of perforations.

Mineral trioxide aggregate (MTA) is the most frequently used repair material in endodontics, but the long setting time and reduced mechanical strength in acidic environments are major shortcomings. In this study, a novel sol-gel-derived calcium silicate cement (sCSC) was developed using an initial Ca/Si molar ratio of 3, with the most effective mixing orders of reactants and optimal HNO3 catalyst volumes. A Fourier transform infrared spectrometer, scanning electron microscope with energy-dispersive X-ray spectroscopy, and X-ray powder diffractometer were used for material characterization. The setting time, compressive strength, and microhardness of sCSC after hydration in neutral and pH 5 environments were compared with that of MTA. Results showed that sCSC demonstrated porous microstructures with a setting time of ~30 min, and the major components of sCSC were tricalcium silicate, dicalcium silicate, and calcium oxide. The optimal formula of sCSC was sn200, which exhibited significantly higher compressive strength and microhardness than MTA, irrespective of neutral or pH 5 environments. In addition, both sn200 and MTA demonstrated good biocompatibility because cell viability was similar to that of the control. These findings suggest that sn200 merits further clinical study for potential application in endodontic repair of perforations.