Sidechain control of porosity closure in multiple peptide-based porous materials by cooperative folding

Porous materials find application in separation, storage and catalysis. We report a crystalline porous solid formed by coordination of metal centres with a glycylserine dipeptide. We prove experimentally that the structure evolves from a solvated porous into a non-porous state as result of ordered displacive and conformational changes of the peptide that suppress the void space in response to environmental pressure. This cooperative closure, which recalls the folding of proteins, retains order in three-dimensions and is driven by the hydroxyl groups acting as H-bond donors in the peptide sequence through the serine residue. This ordered closure is also displayed by multipeptide solid solutions in which the combination of different sequences of amino acids controls their guest response in a non-linear way. This functional control can be compared to the effect of single point mutations in proteins, where the exchange of single amino acids can radically alter structure and functio

Multinuclear solid-state NMR characterization of the Bronsted/Lewis acid properties in the BP HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieve using adsorbed TMPO and TBPO probe molecules

The acid properties of a dehydrated borosilicate, HAMS-1B (H-[B]-ZSM-5), including the acid types, strengths, location, and quantities are investigated by means of trialkylphosphine oxides through multinuclear ID/2D MAS NMR experiments. B-11 DQF-STMAS combined with H-1 MAS NMR studies revealed B-OH and distinct Si-OH protons associated with trigonal boron. P-31 NMR spectra of TMPO-treated HAMS-1B reveal three Bronsted and three Lewis acid sites. We have found a number of limitations applying the TMPO/TBPO method to identify internal/external acidity. Therefore, we propose a new approach to unambiguously discriminate external/internal acid sites by treating a pore-free and pore-blocked HAMS-1B zeolite. This method provided unique structural insight regarding the identification of boron species/coordinations associated with Bronsted/Lewis acid sites. Additionally, ICP analysis in tandem with solid-state NMR enabled full assignment of the detected internal/external acid species and the study of their acid strength. Moreover, we identify the nature of TMPO complexes arising from Bronsted/Lewis interactions. (C) 2014 Elsevier Inc. All rights reserved

Probing the molecular level structure in aluminum containing bifunctional mesoporous organosilicas: A solid-state NMR study

Aluminum containing-CH2CH2-/-CH=CH-PMOs have been synthesized and fully characterized at both the macro- and molecular level using PXRD, N2 adsorption and solid-state NMR. 1H- 29Si HETCOR experiments confirmed the homogenous distribution of organic functionalities within the framework. Whereas 1H- 27Al HETCOR NMR indicated the aluminum to be evenly distributed throughout the framework and located near both organic bridges

Solid acid catalysts based on H3PW12O40 heteropoly acid: Acid and catalytic properties at a gas–solid interface

Solid acid catalysts prepared by supporting 15 wt%H3PW12O40 heteropoly acid (HPA) on TiO2, ZrO2 and Nb2O5 with a sub-monolayer HPA coverage were characterised at a gas–solid interface, regarding their acid properties and chemical structure of HPA on the catalyst surface and compared to “standard” HPA catalysts such as bulk and silica-supported H3PW12O40 and Cs2.5H0.5PW12O40. In contrast to the parent acid, H3PW12O40, possessing strong Brønsted acid sites, the catalysts supported on TiO2, ZrO2 and Nb2O5 have both Brønsted and Lewis acid sites, with the latter mainly originating from the oxide support. The strength of acid sites in these catalysts is weaker than that in H3PW12O40 and Cs2.5H0.5PW12O40. The catalytic activity (turnover frequency) in gas-phase isopropanol dehydration decreases in the order: H3PW12O40 > Cs2.5H0.5PW12O40 > 15%H3PW12O40/SiO2 > 15%H3PW12O40/TiO2 > 15%H3PW12O40/Nb2O5 > 15%H3PW12O40/ZrO2, which is in line with the acid strength as determined by NH3 adsorption calorimetry. Ammonia adsorption calorimetry, 31P{1H} MAS NMR and FTIR indicate increasing interaction between support and HPA in the following order of supports: SiO2 < TiO2 < Nb2O5 < ZrO2. -------------------------------------------------------------------------------

Boron removal and reinsertion studies in B-10-B-11 exchanged HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieves using solid-state NMR

Novel atomic-level insight in boron removal and reinsertion into the framework of a HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieve was obtained by a combination of wet chemistry and one-/twodimensional B-11 solid-state NMR (SSNMR) spectroscopy. Uncalcined HAMS-1B shows only tetrahedral boron. However, three boron species are observed in B-11 SSNMR spectra of as-prepared and then calcined HAMS-1B: tetrahedral framework boron (B-[4](fr)), trigonal framework boron (B-[3](fr)), and non-framework trigonal boron (B-[3](NF)). A picture has emerged as to the origins of these three species. Trigonal boron species are formed via hydrolysis by reaction with the water formed from water release and water formed by oxidation and removal of the template during calcination. The trigonal boron species are readily removed from the framework by slurrying in water or mild acid solutions. Tetrahedral boron remains at a concentration about equal to that in the calcined sieve not slurried, indicating that it is more difficult to remove. The extent of boron removal and reinsertion is pH dependent. We demonstrate that boron is removed to a greater extent at low pH and can be reinserted when pH is increased. Boron reinsertion into the framework is proven by B-11 SSNMR on a series of B-10-B-11 exchanged borosilicate zeolites. We found that when boron is reinserted it enters at higher concentrations (similar to 40% more) as tetrahedral boron, not trigonal boron, thus reversing partial hydrolysis and removal during calcination. (C) 2015 Elsevier Inc. All rights reserved

Ethenylene-Bridged Periodic Mesoporous Organosilicas: FromEtoZ

A novel class of periodic mesoporous organosilicas with E- and/or Z-configured ethenylene bridges was prepared under acidic conditions using the triblock copolymer Pluronic P123 as a structure directing agent. The isomeric configuration of the precursor has a drastic effect on the properties of the resulting PMO materials. The diastereoisomerically pure E-configured ethenylene bridged PMOs reveal higher structural ordering, narrower pore size distributions, and enhanced hydrothermal stability than their diastereoisomerically impure counterparts. These properties have been correlated with the molecular level structure of pore walls probed by solid-state NMR spectroscopy

Sulfonated Graphene Oxide as Effective Catalyst for Conversion of 5-( Hydroxymethyl)-2-furfural into Biofuels

The acid-catalyzed reaction of 5-(hydroxymethyl)-2-furfural with ethanol is a promising route to produce biofuels or fuel additives within the carbohydrate platform; specifically, this reaction may give 5-ethoxymethylfurfural, 5-(ethoxymethyl)furfural diethylacetal, and/or ethyl levulinate (bioEs). It is shown that sulfonated, partially reduced graphene oxide (S-RGO) exhibits a more superior catalytic performance for the production of bioEs than several other acid catalysts, which include sulfonated carbons and the commercial acid resin Amberlyst-15, which has a much higher sulfonic acid content and stronger acidity. This was attributed to the cooperative effects of the sulfonic acid groups and other types of acid sites (e.g., carboxylic acids), and to the enhanced accessibility to the active sites as a result of the 2D structure. Moreover, the acidic functionalities bonded to the S-RGO surface were more stable under the catalytic reaction conditions than those of the other solids tested, which allowed its efficient reuse

A water-stable porphyrin-based metal-organic framework active for visible-light photocatalysis

Light-harvesting MOFs: A new porous porphyrinic metal-organic framework (MOF; see picture) was obtained by hydrothermal synthesis. The chemical and thermal stability of the material allows a postsynthetic insertion of zinc in the center of the porphyrin. The visible-light photocatalytic activity of this porphyrin-based material is shown for the sacrificial hydrogen evolution from water

Melilite glass-ceramic sealants for solid oxide fuel cells: effects of ZrO2 additions assessed by microscopy, diffraction and solid-state NMR

The influence of adding 0-5 mol% zirconia (ZrO2) to a series of melt-quenched alkaline-earth aluminosilicate glasses designed in the gehlenite (Ca2Al2SiO7)-akermanite (Ca2MgSi2O7) system has been investigated for their potential application as sealants for solid oxide fuel cells (SOFCs). The work was implemented with a dual aim of improving the sintering ability of the glass system under consideration and gaining insight into the structural changes induced by ZrO2 additions in the glasses consequentially leading to their enhanced long-term thermal stability. That the degree of condensation of SiO4 tetrahedra increased with increasing amounts of zirconia was confirmed by Si-29 magic-angle (MAS) NMR. 1D Al-27, B-11 MAS as well as two-dimensional (2D) B-11 MQMAS/STMAS NMR experiments gave structural insight into the number and nature of aluminum and boron sites found in the glass and glass-ceramic (GC) samples. Irrespective of the heat treatment time, increasing the zirconia content in glasses suppressed their tendency towards devitrification, while the glasses exhibited good sintering behavior resulting in mechanically strong GCs with higher amounts of residual glassy phase making them suitable for self-healing during SOFC operation. All the GCs exhibited low total electrical conductivity; appropriate coefficients of thermal expansion (CTE), good joining and minimal reactivity with SOFC metallic components at the fuel cell operating temperature, thus, qualifying them for further appraisal in SOFC stacks

Mesoporous carbon-silica solid acid catalysts for producing useful bio-products within the sugar-platform of biorefineries

Useful bio-products are obtainable via the catalytic conversion of biomass or derived intermediates as renewable carbon sources. In particular, furanic ethers and levulinate esters (denoted bioEs) have wide application profiles and can be synthesised via acid-catalysed reactions of intermediates such as fructose, 5-hydroxymethyl-2-furaldehyde (HMF) and furfuryl alcohol (FA) with ethanol. Solid acid catalysts are preferred for producing the bioEs with environmental benefits. Furthermore, the versatility of the catalyst in obtaining the bioEs from different intermediates is attractive for process economics, and in the case of porous catalysts, large pore sizes can be beneficial for operating in the kinetic regime. Carbon-based materials are attractive acid catalysts due to their modifiable surface, e.g. with relatively strong sulfonic acid groups (SO3H). Considering these aspects, here, we report the preparation of mesoporous (SO3H)-functionalised-carbon/silica (C/S) composites with large pores and high amounts of acid sites (up to 2.3 mmol g(-1)), and their application as versatile solid acid catalysts for producing bioEs from fructose, HMF and FA. The mesoporous composites were prepared by activation of an organic compound deposited on the ordered mesoporous silicas MCF (mesostructured cellular foam) and SBA-15, where the organic compound (p-toluenesulfonic acid) acted simultaneously as the carbon and SO3H source. The atomic-level characterisation of the acid nature and strengths was performed by P-31 solid-state NMR studies of an adsorbed base probe, in combination with FT-IR and XPS. Comparative catalytic studies showed that the C/S composites are interesting catalysts for obtaining bioEs in high yields, in comparison with classical solid acid catalysts such as sulfonic acid resin Amberlyst (TM)-15 and nanocrystalline (large pore) zeolite H-beta