Zeolites and zeolite-like materials are continually finding new applications. Because of the uniformity of these solids, the expression of macroscale materials properties that are controlled by the ...materials chemistry at the atomic/molecular scale are achievable. In this Perspective, I discuss the following areas of current interest in zeolites and zeolite-like materials that rely on manipulation of the materials chemistry for their preparation and provide new opportunities for application: (i) exploitation of organic structure-directing agents (SDAs) for new materials, (ii) the synthesis of zeolites without SDAs, (iii) the synthesis of very hydrophobic materials, (iv) conversions of two-dimensional (2D) to 3D materials and vice versa, (v) hierarchically organized materials, (vi) chiral materials, and (vii) direction of tetrahedral atoms to specific framework positions.
In the past decade or so, small-pore zeolites have received greater attention than large- and medium-pore molecular sieves that have historically dominated the literature. This is primarily due to ...the commercialization of two major catalytic processes, NOx exhaust removal and methanol conversion to light olefins, that take advantage of the properties of these materials with smaller apertures. Small-pore zeolites possess pores that are constructed of eight tetrahedral atoms (Si4+ and Al3+), each time linked by a shared oxygen These eight-member ring pores (8MR) provide small molecules access to the intracrystalline void space, e.g., to NOx during car exhaust cleaning (NOx removal) or to methanol en route to its conversion into light olefins, while restricting larger molecule entrance and departure that is critical to overall catalyst performance. In total, there are forty-four structurally different small-pore zeolites. Forty-one of these zeolites can be synthesized, and the first synthetic zeolite (KFI, 1948) was in fact a small-pore material. Although the field of 8MR zeolite chemistry has expanded in many directions, the progress in synthesis is framework-specific, leaving insights and generalizations difficult to realize. This review first focuses on the relevant synthesis details of all 8MR zeolites and provides some generalized findings and related insights. Next, catalytic applications where 8MR zeolites either have been commercialized or have dominated investigations are presented, with the aim of providing structure–activity relationships. The review ends with a summary that discusses (i) both synthetic and catalytic progress, (ii) a list of opportunities in the 8MR zeolite field, and (iii) a brief future outlook.
Experimental therapeutics developed to exploit RNA interference (RNAi) are now in clinical studies. Here, the translation from concept to clinic for the first experimental therapeutic to provide ...targeted delivery of synthetic, small interfering RNA (siRNA) in humans is described. This targeted, nanoparticle formulation of siRNA, denoted as CALAA-01, consists of a cyclodextrin-containing polymer (CDP), a polythethylene glycol (PEG) steric stabilization agent, and human transferrin (Tf) as a targeting ligand for binding to transferrin receptors (TfR) that are typically upregulated on cancer cells. The four component formulation is self-assembled into nanoparticles in the pharmacy and administered intravenously (iv) to patients. The designed features of this experimental therapeutic are described, and their functions illustrated.
This paper explores the evolving renewable energy ‘prosumer’ phenomenon in the United Kingdom (UK). It identifies and evaluates how prosumer business models can exist beyond direct subsidy and the ...range of prosumer business model archetypes currently in operation. Through a series of in-depth interviews and document analysis, the paper identifies the key opportunities and challenges for these innovative energy business models. The analysis shows that recent developments in technology such as the diffusion of smart meters, li-ion batteries, peer-to-peer trading platforms and electric vehicles are opening up a range of new value propositions, which in turn are beginning to be exploited by a range of new business models. In many cases the regulatory, financing and institutional governance landscape of the UK lags behind, however, inhibiting these emerging business models. Moreover, these business models rely on managing a complex set of values for consumers that reach deeper into their lives than traditional tariffs. Thus, successful business models must manage this complexity if they are to be adopted by the disengaged majority. Energy policy and energy practitioners can leverage these emerging trends in service of a low carbon energy transition by adopting ‘ten principles’ of prosumerism; and six UK policy recommendations.
•Prosumers –who produce and consume renewable energy – are key actors in energy transitions.•Traditional prosumer business models are increasingly unviable without subsidies.•New business models should play an increasing role in this post subsidy environment.•These include microgrids; local energy companies; P2P, aggregators, ESCOs and V2G models.•We outline drivers and barriers for these models and propose ‘10 principles of prosumerism’.
Most therapeutic agents are excluded from entering the central nervous system by the blood–brain barrier (BBB). Receptor mediated transcytosis (RMT) is a common mechanism used by proteins, including ...transferrin (Tf), to traverse the BBB. Here, we prepared Tf-containing, 80-nm gold nanoparticles with an acid-cleavable linkage between the Tf and the nanoparticle core to facilitate nanoparticle RMT across the BBB. These nanoparticles are designed to bind to Tf receptors (TfRs) with high avidity on the blood side of the BBB, but separate from their multidentate Tf–TfR interactions upon acidification during the transcytosis process to allow release of the nanoparticle into the brain. These targeted nanoparticles show increased ability to cross an in vitro model of the BBB and, most important, enter the brain parenchyma of mice in greater amounts in vivo after systemic administration compared with similar high-avidity nanoparticles containing noncleavable Tf. In addition, we investigated this design with nanoparticles containing high-affinity antibodies (Abs) to TfR. With the Abs, the addition of the acid-cleavable linkage provided no improvement to in vivo brain uptake for Ab-containing nanoparticles, and overall brain uptake was decreased for all Ab-containing nanoparticles compared with Tf-containing ones. These results are consistent with recent reports of high-affinity anti-TfR Abs trafficking to the lysosome within BBB endothelium. In contrast, high-avidity, Tf-containing nanoparticles with the acid-cleavable linkage avoid major endothelium retention by shedding surface Tf during their transcytosis.
Terephthalic acid (PTA), a monomer in the synthesis of polyethylene terephthalate (PET), is obtained by the oxidation of petroleum-derived p-xylene. There is significant interest in the synthesis of ...renewable, biomass-derived PTA. Here, routes to PTA starting from oxidized products of 5-hydroxymethylfurfural (HMF) that can be produced from biomass are reported. These routes involve Diels-Alder reactions with ethylene and avoid the hydrogenation of HMF to 2,5-dimethylfuran. Oxidized derivatives of HMF are reacted with ethylene over solid Lewis acid catalysts that do not contain strong Brønsted acids to synthesize intermediates of PTA and its equally important diester, dimethyl terephthalate (DMT). The partially oxidized HMF, 5-(hydroxymethyl)furoic acid (HMFA), is reacted with high pressure ethylene over a pure-silica molecular sieve containing framework tin (Sn-Beta) to produce the Diels-Alder dehydration product, 4-(hydroxymethyl)benzoic acid (HMBA), with 31% selectivity at 61% HMFA conversion after 6 h at 190 °C. If HMFA is protected with methanol to form methyl 5-(methoxymethyl)furan-2-carboxylate (MMFC), MMFC can react with ethylene in the presence of Sn-Beta for 2 h to produce methyl 4-(methoxymethyl) benzenecarboxylate (MMBC) with 46% selectivity at 28% MMFC conversion or in the presence of a pure-silica molecular sieve containing framework zirconium (Zr-Beta) for 6 h to produce MMBC with 81% selectivity at 26% MMFC conversion. HMBA and MMBC can then be oxidized to produce PTA and DMT, respectively. When Lewis acid containing mesoporous silica (MCM-41) and amorphous silica, or Brønsted acid containing zeolites (Al-Beta), are used as catalysts, a significant decrease in selectivity/yield of the Diels-Alder dehydration product is observed.
Small interfering RNA (siRNA)-based therapies are emerging as a promising new anticancer approach, and a small number of Phase I clinical trials involving patients with solid tumours have now been ...completed. Encouraging results from these pioneering clinical studies show that these new therapeutics can successfully and safely inhibit targeted gene products in patients with cancer, and have taught us important lessons regarding appropriate dosages and schedules. In this Review, we critically assess these Phase I studies and discuss their implications for future clinical trial design. Key challenges and future directions in the development of siRNA-containing anticancer therapeutics are also considered.
Engineered systems designed to remove CO
2
from the atmosphere need better adsorbents. Here, we report on zeolite-based adsorbents for the capture of low-concentration CO
2
. Synthetic zeolites with ...the mordenite (MOR)-type framework topology physisorb CO
2
from low concentrations with fast kinetics, low heat of adsorption, and high capacity. The MOR-type zeolites can have a CO
2
capacity of up to 1.15 and 1.05 mmol/g for adsorption from 400 ppm CO
2
at 30 °C, measured by volumetric and gravimetric methods, respectively. A structure–performance study demonstrates that Na
+
cations in the O33 site located in the side-pocket of the MOR-type framework, that is accessed through a ring of eight tetrahedral atoms (either Si
4+
or Al
3+
: eight-membered ring 8MR), is the primary site for the CO
2
uptake at low concentrations. The presence of N
2
and O
2
shows negligible impact on CO
2
adsorption in MOR-type zeolites, and the capacity increases to ∼2.0 mmol/g at subambient temperatures. By using a series of zeolites with variable topologies, we found the size of the confining pore space to be important for the adsorption of trace CO
2
. The results obtained here show that the MOR-type zeolites have a number of desirable features for the capture of CO
2
at low concentrations.
The capture of low concentration CO2 presents numerous challenges. Here, we report that zinc containing chabazite (CHA) zeolites can realize high capacity, fast adsorption kinetics, and low ...desorption energy when capturing ca. 400 ppm CO2. Control of the state and location of the zinc ions in the CHA cage is critical to the performance. Zn2+ loaded onto paired anionic sites in the six‐membered rings (6MRs) in the CHA cage are the primary sites to adsorb ca. 0.51 mmol CO2/g‐zeolite with Si/Al=ca. 7, a 17‐fold increase compared to the parent H‐form. The capacity is increased further to ca. 0.67 mmol CO2/g‐zeolite with Si/Al=ca. 2 due to more paired sites for zinc exchange. Zeolites with double six‐membered rings (D6MRs) that orient 6MRs into the cages give enhanced uptakes for CO2 adsorption with zinc exchange. The results reveal that zinc exchanged CHA and several other small pore, cage containing zeolites merit further investigation for the capture of low concentration CO2.
Low concentration CO2 is adsorbed in zinc containing CHA‐type zeolites with a high capacity of 0.67 mmol CO2/g‐zeolite. The materials exhibit higher CO2 capacity, faster kinetics, lower desorption energy than low‐silica 13X zeolites. Zeolite framework and the states and locations of zinc ions play crucial roles in the adsorption performance.
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•Glucose and lactose isomerization are catalyzed by Lewis acidic zeolites.•Order-of-magnitude higher turnover rates on hydrophobic than hydrophilic solids.•Reactant diffusion does not ...limit rates even when pores are filled with solvent.•Rate constants reflect transition state stability relative to bound solvent.•Solvent molecules bind more strongly at Ti centers in defective environments.
Lewis acid sites isolated within low-defect, hydrophobic molecular sieves (Sn-Beta-F, Ti-Beta-F) catalyze monosaccharide (glucose–fructose) and disaccharide (lactose–lactulose) aldose–ketose isomerization reactions in liquid water at initial turnover rates (per total metal atom; 373K) that are, respectively, ∼10–30 and ∼103–104 factors higher than sites isolated within highly defective, hydrophilic molecular sieves (Ti-Beta-OH) or amorphous co-precipitated oxides (TiO2–SiO2). Glucose-H2/glucose-D2 kinetic isotope effects of ∼2 (at 373K) for intramolecular C2–C1 hydride shift isomerization to fructose indicate that glucose transport to active sites within Ti-Beta-F or Ti-Beta-OH does not limit turnover rates in liquid water or methanol, in spite of dramatic differences in the volumetric occupation of hydrophobic and hydrophilic void spaces by physisorbed solvent molecules. Glucose isomerization turnover rates (per total Ti; 373K) in liquid water are first-order in aqueous glucose concentration (at least up to 1.5% (w/w)). The mechanistic interpretation of measured first-order isomerization rate constants indicates that they reflect free energies of kinetically relevant isomerization transition states relative to two bound solvent molecules, which adsorb competitively with sugars at Lewis acid sites and are the most abundant surface intermediates during steady-state catalysis. The lower isomerization rate constants on Ti centers in highly defective environments, in part, reflect stronger coordination of solvent molecules to Ti centers via additional hydrogen bonding interactions with proximal surface hydroxyl groups. The direct measurement of glucose isomerization rate constants in the liquid phase provides a rigorous and quantitative description of the catalytic differences prevalent among Lewis acidic silica-based solids with hydrophobic or hydrophilic properties, and their interpretation using a mechanism-based rate equation provides further clarity into the inhibition of catalytic turnovers at Lewis acid sites by solvent coordination.
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