Strong Swelling and Symmetrization in Siliceous Zeolites due to Hydrogen Insertion at High Pressure.

Hydrogen and helium saturate the 1D pore systems of the high-silica (Si/Al>30) zeolites Theta-One (TON), and Mobile-Twelve (MTW) at high pressure based on x-ray diffraction, Raman spectroscopy and Monte Carlo simulations. In TON, a strong 22% volume increase occurs above 5 GPa with a transition from the collapsed P21 to a symmetrical, swelled Cmc21 form linked to an increase in H2 content from 12 H2/unit cell in the pores to 35 H2/unit cell in the pores and in the framework of the material. No transition and continuous collapse of TON is observed in helium indicating that the mechanism of H2 insertion is distinct from other fluids. The insertion of hydrogen in the larger pores of MTW results in a strong 11% volume increase at 4.3 GPa with partial symmetrization followed by a second volume increase of 4.5% at 7.5 GPa, corresponding to increases in hydrogen content from 43 to 67 and then to 93 H2/unit cell. Flexible 1D siliceous zeolites have a very high H2 capacity (1.5 and 1.7 H2/SiO2 unit for TON and MTW, respectively) due to H2 insertion in the pores and the framework, in contrast to other atoms and molecules, thereby providing a mechanism for strong swelling.

Emergence of Order in Origin-of-Life Scenarios on Mineral Surfaces: Polyglycine Chains on Silica.

The polymerization of amino acids (AAs) to peptides on oxide surfaces has attracted interest owing to its high importance in biotechnology, prebiotic chemistry, and origin of life theories. However, its mechanism is still poorly understood. We tried to elucidate the reactivity of glycine (Gly) from the vapor phase on the surface of amorphous silica under controlled atmosphere at 160 °C. Infrared (IR) spectroscopy reveals that Gly functionalizes the silica surface through the formation of ester species, which represent, together with the weakly interacting silanols, crucial elements for monomers activation and polymerization. Once activated, ß-turns start to form as initiators for the growth of long linear polypeptides (poly-Gly) chains, which elongate into ordered structures containing both ß-sheet and helical conformations. The work also points to the role of water vapor in the formation of further self-assembled ß-sheet structures that are highly resistant to hydrolysis.

Preparation of Confined One-Dimensional Boron Nitride Chains in the 1-D Pores of Siliceous Zeolites under High-Pressure, High-Temperature Conditions.

Low-dimensional boron nitride (BN) chains were prepared in the one-dimensional pores of the siliceous zeolites theta-one (TON) and Mobil-twelve (MTW) by the infiltration, followed by the dehydrocoupling and pyrolysis of ammonia borane under high-pressure, high-temperature conditions. High-pressure X-ray diffraction in a diamond anvil cell and in a large-volume device was used to follow in situ these different steps in order to determine the optimal conditions for this process. Based on these results, millimeter-sized samples of BN/TON and BN/MTW were synthesized. Characteristic B-N stretching vibrations of low-dimensional BN were observed by infrared and Raman spectroscopies. The crystal structures were determined using a combination of X-ray diffraction and density functional theory with one and two one-dimensional zig-zag (BN)x chains per pore in BN/TON and BN/MTW, respectively. These 1-D BN chains potentially have interesting photoluminescence properties in the far ultraviolet region of the electromagnetic spectrum.

Design, Characterization and Applications of Functional Nanomaterials.

Nanomaterials are commonly defined as particles existing in nature or artificially manufactured materials that have one or more external dimensions in the 1-100 nm range [...].

Amino acid encapsulation in zeolite MOR: Effect of spatial confinement.

In this study the absorption of glycine, α-alanine and ß-alanine amino acids into the pores of the synthetic zeolite Na-mordenite was investigated with the aim of: (i) evaluating the effectiveness of the MOR framework type in amino acid adsorption (via vapor and aqueous loading); (ii) understanding the host-guest and guest-guest interactions to possibly design a tailor made material and a loading procedure able to maximize the amino acid adsorption; (iii) studying the effect of pressure on the adsorbed amino acids such as, for instance, possible amino acid condensation. The structural characterization, carried out with the combination of diffractometric and infrared spectroscopy analyses, shows that MOR can adsorb amino acids, which are found both in protonated/deprotonated (possibly also generating zwitterions) form. Vapor loading is ineffective for α-alanine, while it is effective in ß-alanine and glycine adsorption, even if using different loading degrees. The shape and size of MOR channels make this zeolite suitable to accommodate a peptide. In a glycine loaded sample some molecules condensate to form cyclic dimers, while linear oligomers are detected only in a ß-alanine MOR hybrid. The sample loaded with α-L-alanine from aqueous solution does not show the presence of amide bond signals, indicating that the molecules are mostly hosted in zwitterionic form in Na-MOR channels. The application of external baric stimuli does not induce substantial modifications in the structure of the glycine loaded zeolite; this result may be explained by the low number of molecules hosted in the channels. The amino acid amount within the zeolite pores is the most important reactivity parameter and an increased loading could induce chemical modifications.

High-Pressure Synthesis and Gas-Sensing Tests of 1-D Polymer/Aluminophosphate Nanocomposites.

Recently, filling zeolites with gaseous hydrocarbons at high pressures in diamond anvil cells has been carried out to synthesize novel polymer-guest/zeolite-host nanocomposites with potential, intriguing applications, although the small amount of materials, 10-7 cm3, severely limited true technological exploitation. Here, liquid phenylacetylene, a much more practical reactant, was polymerized in the 12 Å channels of the aluminophosphate Virginia Polytechnic Institute-Five (VFI) at about 0.8 GPa and 140 °C, with large volumes in the order of 0.6 cm3. The resulting polymer/VFI composite was investigated by synchrotron X-ray diffraction and optical and 1H, 13C, and 27Al nuclear magnetic resonance spectroscopy. The materials, consisting of disordered π-conjugated polyphenylacetylene chains in the pores of VFI, were deposited on quartz crystal microbalances and tested as gas sensors. We obtained promising sensing performances to water and butanol vapors, attributed to the finely tuned nanostructure of the composites. High-pressure synthesis is used here to obtain an otherwise unattainable true technological material.

Nearly free surface silanols are the critical molecular moieties that initiate the toxicity of silica particles.

Inhalation of silica particles can induce inflammatory lung reactions that lead to silicosis and/or lung cancer when the particles are biopersistent. This toxic activity of silica dusts is extremely variable depending on their source and preparation methods. The exact molecular moiety that explains and predicts this variable toxicity of silica remains elusive. Here, we have identified a unique subfamily of silanols as the major determinant of silica particle toxicity. This population of "nearly free silanols" (NFS) appears on the surface of quartz particles upon fracture and can be modulated by thermal treatments. Density functional theory calculations indicates that NFS locate at an intersilanol distance of 4.00 to 6.00 Å and form weak mutual interactions. Thus, NFS could act as an energetically favorable moiety at the surface of silica for establishing interactions with cell membrane components to initiate toxicity. With ad hoc prepared model quartz particles enriched or depleted in NFS, we demonstrate that NFS drive toxicity, including membranolysis, in vitro proinflammatory activity, and lung inflammation. The toxic activity of NFS is confirmed with pyrogenic and vitreous amorphous silica particles, and industrial quartz samples with noncontrolled surfaces. Our results identify the missing key molecular moieties of the silica surface that initiate interactions with cell membranes, leading to pathological outcomes. NFS may explain other important interfacial processes involving silica particles.

The Case of Formic Acid on Anatase TiO2 (101): Where is the Acid Proton?

Carboxylic-acid adsorption on anatase TiO2 is a relevant process in many technological applications. Yet, despite several decades of investigations, the acid-proton localization-either on the molecule or on the surface-is still an open issue. By modeling the adsorption of formic acid on top of anatase(101) surfaces, we highlight the formation of a short strong hydrogen bond. In the 0 K limit, the acid-proton behavior is ruled by quantum delocalization effects in a single potential well, while at ambient conditions, the proton undergoes a rapid classical shuttling in a shallow two-well free-energy profile. This picture, supported by agreement with available experiments, shows that the anatase surface acts like a protecting group for the carboxylic acid functionality. Such a new conceptual insight might help rationalize chemical processes involving carboxylic acids on oxide surfaces.

Does the Abiotic Formation of Oligopeptides on TiO2 Nanoparticles Require Special Catalytic Sites? Apparently Not.

The oligomerization of non-activated amino acids catalyzed by nanostrucrured mineral oxide surfaces holds promises as a sustainable route for the industrial production of polypeptides. To analyze the influence of the surface type on the catalytic process, we performed, via a mild Chemical Vapor Deposition approach, the oligomerization of Glycine on two samples of TiO2 nanoparticles characterized by different relative amounts of defective surface terminations. Based on infrared spectroscopy and mass spectrometry data, we show herein that the formation of peptide bonds on titania nanoparticles does not require highly energetic surface terminations, but can occur also on the most abundant and thermodynamically most stable {101} facets of nanosized anatase.

The formation and self-assembly of long prebiotic oligomers produced by the condensation of unactivated amino acids on oxide surfaces.

In situ IR and mass spectrometry evidence for the catalytic formation on SiO2 and TiO2 surfaces of glycine oligomers (poly-Gly) up to 16 units long by successive feeding with monomers from the vapor phase is presented. Parallel experiments carried out on hydroxyapatite resulted in the unreactive adsorption of Gly, thus indicating that the oligomerization was specifically catalyzed by the surfaces of SiO2 and TiO2 . Furthermore, the poly-Gly moved on the surface when contacted with H2 O vapor and formed self-assembled aggregates containing both helical and ß-sheet-like structural motifs. These results indicate that polypeptides formed by the condensation of amino acids adsorbed on a mineral surface can evolve into structured supramolecular assemblies.