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Current CO2 separation technologies by liquid solvents suffer from either high regeneration costs or low selectivity/capacity of the solvent. Dispersing ca. 12.5 wt% CO2-selective zeolite rho solid into the commercial CO2 capture solvent Genosorb® converts it into a porous liquid with at least 2.5 times greater CO2 capacity and CO2/CH4 selectivity compared to Genosorb® itself. This is predicted to result in more economical separation processes, particularly for biogas upgrading.

Porous materials contain regions of empty space into which guest molecules can be selectively adsorbed and sometimes chemically transformed. This has made them useful in both industrial and domestic applications, ranging from gas separation, energy storage and ion exchange to heterogeneous catalysis and green chemistry. Porous materials are often ordered (crystalline) solids. Order—or uniformity—is frequently held to be advantageous, or even pivotal, to our ability to engineer useful properties in a rational way. Here we highlight the growing evidence that topological disorder can be useful in creating alternative properties in porous materials. In particular, we highlight here several concepts for the creation of novel porous liquids, rationalize routes to porous glasses and provide perspectives on applications for porous liquids and glasses. Highly ordered crystalline porous solids are useful for many applications. This Perspective explores the evolution of these systems from the ordered state to the glassy and liquid states, discusses the different types of porous liquid and considers possible applications of these disordered systems.

It remains a challenge to detect n-alkanes, which contain only C–C and C–H groups. Herein pillararene sensors are developed toward n-alkane vapours. Fluorescence properties involving aggregation-induced emission have been innovatively demonstrated for pillar[5]arene compounds, including dimethoxypillar[5]arene (DMP[5]), difunctionalized (DBP[5] and DAP[5]) and perfunctionalized pillar[5]arene compounds (DEOP[5] and EOP[5]). The longer-wavelength emission at around 450 nm endows pillar[5]arene films with the ability to respond visually to various VOC (volatile organic compound) gases. DMP[5] and DEOP[5] films display fluorescent responses to nitrobenzene with high sensitivities (140 and 50 ppb). Notably, the luminescence of a transparent difunctionalized DBP[5] film displays both significant enhancements in fluorescence intensity and reduction in transparency toward n-alkane vapours (hexane, pentane and heptane) owing to host–guest interactions. The film sensors exhibit good recyclability in VOC sensing. The results highlight an innovative strategy to develop responsive sensors toward alkane vapours that are difficult to detect.

A continuous, scalable, and solvent-free method for the synthesis of various naphthalic imides and perylene diimides (PDIs) using twin-screw extrusion (TSE) is reported. Using TSE, naphthalic imides were obtained quantitatively without the need for excess amine reactant or product purification. With good functional-group tolerance, alkyl and benzyl amine derived PDIs (incl. commercial dyes) were obtained in 50-99 % yield. Use of K2 CO3 , enabled synthesis of more difficult aniline-derived PDIs. Furthermore, an automated continuous TSE process for Pigments Black 31 and 32 is demonstrated, with a throughput rate of about 1500 g day-1 , corresponding to a space time yield of about 30×103 kg m-3 day-1 , which is 1-2 orders of magnitude greater than for solvent-based batch methods. These methods provide substantial waste reductions and improved efficiency compared to conventional solvent-based methods.

A range of Pt and Pt–Re catalysts on titania were mechanochemically prepared and compared to conventional catalysts made by wet impregnation for the selective hydrogenation of stearic acid. Mechanochemically prepared catalysts showed superior selectivity toward stearyl alcohol compared to the conventional catalysts. It was possible to achieve 100% selectivity to stearyl alcohol using mechanochemically prepared Pt/TiO2.

The scale-up of mechanochemical methods could play a transformative role in making manufacturing processes in the pharmaceutical industry greener by eliminating solvent use and recovery. Combined with energy-efficient continuous processing that consolidates reaction steps, mechanochemistry’s environmental and economic benefits may translate across product supply chains. Here, we evaluate numerous sustainability and green chemistry metrics for producing nitrofurantoin, an active pharmaceutical ingredient (API), via mechanochemical continuous twin-screw extrusion (TSE) and conventional solvent-batch synthesis methods. We find a significant reduction in all metrics for TSE including energy, climate change, and human and ecological health, as well as cost due to reducing excess reactant consumption and eliminating solvents while maintaining high product selectivity. In addition, replacing the direct energy source to drive the chemical reaction from mostly thermal to electrical sources does not increase the net life cycle energy consumed to produce functionally equivalent API. We conclude that mechanochemical synthesis via TSE holds multiple sustainability benefits for manufacturing APIs and potentially other chemical products.

Porous Liquids (PLs) are a new class of material that possess both fluidity and permanent porosity. As such they can act as enhanced, selective solvents and may ultimately find applications which are not possible for porous solids, such as continuous flow separation processes. Type II PLs consist of empty molecular hosts dissolved in size-excluded solvents and to date have mainly been based on hosts that have limited chemical and thermal stability. Here we identify Noria, a rigid cyclic oligomer as a new host for the synthesis of more robust Type II PLs. Although the structure of Noria is well-documented, we find that literature has overlooked the true composition of bulk Noria samples. We find that bulk samples typically consist of Noria (ca. 40%), a Noria isomer, specifically a resorcinarene trimer, “R3” (ca. 30%) and other unidentified oligomers (ca. 30%). Noria has been characterised crystallographically as a diethyl ether solvate and its 1H NMR spectrum fully assigned for the first time. The previously postulated but unreported R3 has also been characterised crystallographically as a dimethyl sulfoxide solvate, which confirms its alternative connectivity to Noria. Noria and R3 have low solubility which precludes their use in Type II PLs, however, the partially ethylated derivative Noria-OEt dissolves in the size-excluded solvent 15-crown-5 to give a new Type II PL. This PL exhibits enhanced uptake of methane (CH4) gas supporting the presence of empty pores in the liquid. Detailed molecular dynamics simulations support the existence of pores in the liquid and show that occupation of the pores by CH4 is favoured. Overall, this work revises the general accepted composition of bulk Noria samples and shows that Noria derivatives are appropriate for the synthesis of more robust Type II PLs., Porous Liquids (PLs) are a new class of material that possess both fluidity and permanent porosity. Here we identify Noria, a rigid cyclic oligomer as a new host for the synthesis of more robust Type II PLs.

We describe a series of Type 3 porous liquids, denoted “T3PLs”, based on a wide range of microporous solids including MOFs, zeolites and a porous organic polymer (PAF-1). These solids are dispersed in various non-ionic liquid phases (including silicone oils, triglyceride oils, and polyethylene glycols) which have a range of structures and properties, and that are in many cases sterically excluded from the pores of the solids. Several stable dispersions with high gas uptakes are obtained. We show how these dispersions can be tailored toward important gas separation processes (CO2/CH4, C2H4/C2H6) and applications that require biocompatibility., We describe a series of Type 3 porous liquids, denoted “T3PLs”, based on a wide range of microporous solids including MOFs, zeolites and a porous organic polymer (PAF-1).

The continuous and scalable synthesis of a porous organic cage (CC3), obtained through a 10-component imine polycondensation between triformylbenzene and a vicinal diamine, was achieved using twin screw extrusion (TSE). Compared to both batch and flow syntheses, the use of TSE enabled the large scale synthesis of CC3 using minimal solvent and in short reaction times, with liquid-assisted grinding (LAG) also promoting window-to-window crystal packing to form a 3-D diamondoid pore network in the solid state. A new kinetically trapped [3+5] product was also observed alongside the formation of the targeted [4+6] cage species. Post-synthetic purification by Soxhlet extraction of the as-extruded ‘technical grade’ mixture of CC3 and [3+5] species rendered the material porous.

Metal Organic Frameworks (MOFs) offer unparalleled physical and sorption properties due to their chemical tunability and unmatched porosity. MOFs are consequently envisaged to play a key role in commercial gas storage and separation applications. However, it is essential to tackle their current market entry barriers, if mainstream adoption is to be realised. MOF Technologies is a pioneer in MOF commercialisation and has developed innovative solutions with unprecedented efficiency to bring these materials to market. A continuous, versatile and sustainable one-step production method of MOFs in shaped form is demonstrated for the first time. Its advantages for large-scale production and mass customisation are exemplified and validated with performance evaluation under realistic operating conditions.

We assess the potential for formulating a porous liquid that could be used as a selective solvent for the separation of ethane and ethene. Ethane-ethene separation is performed on very large scales by cryogenic distillation, but this uses large amounts of energy. Solvents that are selective to ethane or ethene could potentially enable more efficient liquid-based separation processes to be developed, but to date such solvents have been elusive. Here, Type 3 porous liquids, which consist of microporous solids dispersed in size-excluded liquid phases, were tailored toward the separation of ethane and ethene. A high selectivity for ethene over ethane (25.6 at 0.8 bar) and a high capacity was achieved for zeolite AgA dispersed in an Ag-containing ionic liquid. Unusually for liquid phases, the selectivity for ethane over ethene (2.55 at 0.8 bar) could also be achieved using either the metal-organic framework (MOF) Cu(Qc)2 (Qc = quinoline-5-carboxylate) dispersed in sesame oil or ZIF-7 in sesame oil, the latter showing gated uptake. The efficiency of the Cu(Qc)2 synthesis was increased by developing a mechanochemical method. The regeneration of Cu(Qc)2 in sesame oil and ZIF-7 in sesame oil was also demonstrated, suggesting that these or similar porous liquids could potentially be applied in cyclic separation processes.

Twin-screw extrusion (TSE) was used to synthesize hydantoin-based active pharmaceutical ingredients (APIs) such as nitrofurantoin and dantrolene, employing minimal or no solvent. Postsynthetic workup was not required. This work demonstrates that solvent-free synthesis can be conducted in a continuous manner for pharmaceutical products.

The oligomerisation of L-amino acids by papain was studied in a mixer ball mill and in a planetary ball mill. The biocatalyst proved stable under the ball milling conditions providing the corresponding oligopeptides in good to excellent yields and with a variable degree of polymerisation. Both parameters were found to be dependent on the reaction conditions and on the nature of the amino acid (specifically on its side-chain size and hydrophobicity). In addition, the chemoenzymatic oligomerisation was demonstrated by utilising twin-screw extrusion technology, which allowed for a scalable continuous process. Finally, the synthesised oligo(L-Leu) 2b proved to be active as a catalyst in the Julia–Colonna enantioselective epoxidation of chalcone derivatives.

We demonstrate a simple method for real-time monitoring of mechanochemical synthesis of metal–organic frameworks, by measuring changes in pressure of gas produced in the reaction. Using this manometric method to monitor the mechanosynthesis of the zeolitic imidazolate framework ZIF-8 from basic zinc carbonate reveals an intriguing feedback mechanism in which the initially formed ZIF-8 reacts with the CO2 byproduct to produce a complex metal carbonate phase, the structure of which is determined directly from powder X-ray diffraction data. We also show that the formation of the carbonate phase may be prevented by addition of excess ligand. The excess ligand can subsequently be removed by sublimation, and reused. This enables not only the synthesis but also the purification, as well as the activation of the MOF to be performed entirely without solvent., We demonstrate a simple method for real-time monitoring of mechanochemical synthesis of metal–organic frameworks, by measuring changes in pressure of gas produced in the reaction.

We describe the synthesis of pharmaceutically relevant co-crystals by solvent-free sonochemistry starting from solid reagents. Employing a standard ultrasonic cleaning bath, quantitative conversions occurred within 20-60 minutes to give co-crystals of paracetamol and aspirin with a range of co-formers. As well as the utility of the method, the work raises interesting mechanistic questions regarding acoustic cavitation with no liquid phase being present.

A fast solvent-free method for the metallation of porphyrins is presented. ZnTPP, NiTPP, CuTPP and FeTPP have been prepared mechanochemically by ball milling hydrated metal acetate salts with meso-tetraphenylporphyrin (H2TPP) in a shaker mill for as little as 20 min with no added solvent, avoiding the need for undesirable solvents and long reaction times normally used in such reactions.

Mechanochemical chemoenzymatic peptide and amide bond formation catalysed by papain was studied by ball milling. Despite the high-energy mixing experienced inside the ball mill, the biocatalyst proved stable and highly efficient to catalyse the formation of α,α- and α,β-dipeptides. This strategy was further extended to the enzymatic acylation of amines by milling, and to the mechanosynthesis of a derivative of the valuable dipeptide L-alanyl-L-glutamine.

Working towards a fundamental description of mechanochemical reactions through the use of classical molecular dynamics simulations. Capturing the transfer of molecules between two non-volatile molecular crystals during mechanochemical events., Although solvent-free mechanochemical synthesis continues to gain ever greater importance, the molecular scale processes that occur during such reactions remain largely uncharacterised. Here, we apply computational modelling to indentations between particles of crystals of aspirin and meloxicam under a variety of conditions to mimic the early stages of their mechanochemical cocrystallisation reaction. The study also extends to the effects of the presence of small amounts of solvent. It is found that, despite the solid crystalline nature of the reactants and the presence of little or no solvent, mixing occurs readily at the molecular level even during relatively low-energy collisions. When indented crystals are subsequently drawn apart, a connective neck formed by a mixture of the reactant molecules is observed, suggesting plastic-like behaviour of the reacting materials. Overall the work reveals some striking new insights including (i) relatively facile mixing of crystals under solvent-free conditions, (ii) no appreciable local temperature increases, (iii) localised amorphisation at the contact region and neck of the reacting crystals, and (iv) small amounts of solvent have relatively little effect during this early stage of the reaction, suggesting that their accelerating effect on the reaction may be exerted at later stages.

Mechanochemistry enabled the selective synthesis of the recherche orange polymorph of Wilkinson's catalyst [RhCl(PPh3)3]. The mechanochemically prepared Rh-complex catalysed the solvent-free dehydrogenation of Me2NH·BH3 in a ball mill. The in situ-generated hydrogen (H2) could be utilised for Rh-catalysed hydrogenation reactions by ball milling.

Macroporous cryogels containing mixtures of two key components of the dermal extracellular matrix, fibrinogen and collagen-derived gelatin, were evaluated for use as dermal tissue regeneration scaffolds. The infiltration of human dermal fibroblasts into these matrices was quantitatively assessed in vitro using a combination of cell culture and confocal laser scanning microscopy. The extent of cellular infiltration, as measured by the number of cells per distance travelled versus time, was found to be positively correlated with the fibrinogen concentration of the cryogel scaffolds; a known potentiator of cell migration and angiogenesis within regenerating tissue. An analysis of the proteins expressed by infiltrating fibroblasts revealed that the cells that had migrated into the interior portion of the scaffolds expressed predominantly F-actin along their cytoplasmic stress fibres, whereas those present on the periphery of the scaffolds expressed predominantly α-smooth muscle actin, indicative of a nonmotile, myofibroblast phenotype associated with wound contraction. In conclusion, the cryogels produced in this study were found to be biocompatible and, by alteration of the fibrinogen content, could be rendered more amenable to cellular infiltration.

Mechanochemical preparation of Ag/Al 2 O 3 catalysts used for the selective catalytic reduction of NO x using hydrocarbons has been shown to substantially increase the activity of the catalyst in comparison with Ag/Al 2 O 3 prepared by wet impregnation. The effect of using different ball-milling experimental parameters on both the structure of the material as well as the catalyst activity has been investigated and the optimum conditions established. A phase transition from γ- to α-alumina was observed milling at high speeds which was found to result in lower catalyst activities. At lower milling speeds both fracturing and agglomeration of the alumina support can be observed depending on the grinding time. However, due to ball-milling, a general enhancement in the NO x reduction activity was observed for all catalysts compared with the conventionally prepared catalysts irrespective of the reductant used. Transient DRIFTS-MS experiments were performed to investigate the effect of H 2 in the absence and presence of water on the SCR reaction over catalysts prepared by both ball milling and wet impregnation. In-situ DRIFTS-MS analysis revealed significant differences in both gas phase and surface species. Most notably, isocyanate species were formed significantly more quickly and at higher surface concentration in the case of the mechanochemically prepared catalyst.

Mechanochemical synthesis has the potential to change the way in which chemistry is conducted, particularly with regard to removing or dramatically reducing the need for solvents. Recently, it has been demonstrated that mechanochemistry can be carried out continuously and on large scale through the use of twin-screw extrusion (TSE). TSE has successfully been applied to the synthesis of cocrystals, metal organic frameworks (MOFs), deep eutectic solvents (DESs), metal complexes, and organic condensation reactions. However, while TSE provides a route for mechanochemical synthesis to be developed into a continuous, high-volume manufacturing process, little is currently understood about how to best optimize the various process parameters involved. Herein, we investigate the use of a batch mixer that has been previously used in polymer processing, to optimize mechanochemical reactions performed by extrusion. In particular, reactions between 8-hydroxyquinoline (Hq) and metal acetate salts of zinc or aluminum to give quinolinate complexes Znq2·AcOH and Alq3·AcOH, which are of interest for organic light-emitting diode (OLED) applications, have been investigated. The manner in which the progress of the reaction correlates with the machine torque, temperature, and specific mechanical energy (SME) imparted by the batch mixer has been elucidated. Significantly, this knowledge enabled optimization of the mechanochemical reactions by TSE through the key parameters of screw speed, feed rate, temperature, and particle size.

Chemical manufacturing typically requires more than one step, involving multiple batch processes, which makes synthesis at scale laborious and wasteful. Herein, we demonstrate that several reactions can be telescoped into a single continuous process and/or be carried out as a continuous multi-component reaction (MCR), by twin screw extrusion (TSE), in the complete absence of solvent.

Although mechanochemical synthesis is becoming more widely applied and even commercialised, greater basic understanding is needed if the field is to progress on less of a trial-and-error basis. We report that a mechanochemical reaction in a ball mill exhibits unusual sigmoidal feedback kinetics that differ dramatically from the simple first-order kinetics for the same reaction in solution. An induction period is followed by a rapid increase in reaction rate before the rate decreases again as the reaction goes to completion. The origin of these unusual kinetics is found to be a feedback cycle involving both chemical and mechanical factors. During the reaction the physical form of the reaction mixture changes from a powder to a cohesive rubber-like state, and this results in the observed reaction rate increase. The study reveals that non-obvious and dynamic rheological changes in the reaction mixture must be appreciated to understand how mechanochemical reactions progress.

A sheet gelatin scaffold with attached silicone pseudoepidermal layer for wound repair purposes was produced by a cryogelation technique. The resulting scaffold possessed an interconnected macroporous structure with a pore size distribution of 131 ± 17 μm at one surface decreasing to 30 ± 8 μm at the attached silicone surface. The dynamic storage modulus (G') and mechanical stability were comparable to the clinical gold standard dermal regeneration template, Integra®. The scaffolds were seeded in vitro with human primary dermal fibroblasts. The gelatin based material was not only non-cytotoxic, but over a 28 day culture period also demonstrated advantages in cell migration, proliferation and distribution within the matrix when compared with Integra®. When seeded with human keratinocytes, the neoepidermal layer that formed over the cryogel scaffold appeared to be more advanced and mature when compared with that formed over Integra®. The in vivo application of the gelatin scaffold in a porcine wound healing model showed that the material supports wound healing by allowing host cellular infiltration, biointegration and remodelling. The results of our in vitro and in vivo studies suggest that the gelatin based scaffold produced by a cryogelation technique is a promising material for dermal substitution, wound healing and other potential biomedical applications.

Pseudomonas aeruginosa is recognised as a major aetiological agent of nosocomial infections, which are associated with multiple-antibiotic resistance. Among many of its important virulence factors is its ability to form biofilms on the surfaces of implantable medical devices and to produce toxic metabolites, pyocyanin, via an intercellular cell density-dependent signalling system of communication. In this study, poly (ε-lysine) dendrons composed of increasingly branching generations were synthesised, characterised, and examined for their effects on virulence factor production in P. aeruginosa. The results show that these hyperbranched poly (ε-lysine) dendrons, in particular the 3rd generation, can increase the efficacy of a conventional antibiotic, ciprofloxacin, and reduce pyocyanin production, with marginal effects on the rate of bacterial replication, suggesting that the observed effects are not due to dendron toxicity. Furthermore, dendron and ciprofloxacin coadministration was identified as the most effective strategy which highlights the potential of peptide-based dendrons as quorum sensing inhibitors.

Although the use of ball milling to induce reactions between solids (mechanochemical synthesis) can provide lower-waste routes to chemical products by avoiding solvent during the reaction, there are further potential advantages in using one-pot multistep syntheses to avoid the use of bulk solvents for the purification of intermediates. We report here two-step syntheses involving formation of salen-type ligands from diamines and hydroxyaldehydes followed directly by reactions with metal salts to provide the corresponding metal complexes. Five salen-type ligands 2,2′-[1,2-ethanediylbis[(E)-nitrilomethylidyne]]bis-phenol, ‘salenH2’, 1; 2,2′-[(±)-1,2-cyclohexanediylbis-[(E)-nitrilomethylidyne]]bis-phenol, 2; 2,2′-[1,2-phenylenebis(nitrilomethylidyne)]-bis-phenol, ‘salphenH2’ 3; 2-[[(2-aminophenyl)imino]methyl]-phenol, 4; 2,2′-[(±)-1,2-cyclohexanediylbis[(E)-nitrilomethylidyne]]-bis[4,6-bis(1,1-dimethylethyl)]-phenol, ‘Jacobsen ligand’, 5) were found to form readily in a shaker-type ball mill at 0.5 to 3 g scale from their corresponding diamine and aldehyde precursors. Although in some cases both starting materials were liquids, ball milling was still necessary to drive those reactions to completion because precipitation of the product and or intermediates rapidly gave in thick pastes which could not be stirred conventionally. The only ligand which required the addition of solvent was the Jacobsen ligand 5 which required 1.75 mol equivalents of methanol to go to completion. Ligands 1–5 were thus obtained directly in 30–60 minutes in their hydrated forms, due to the presence of water by-product, as free-flowing yellow powders which could be dried by heating to give analytically pure products. The one-armed salphen ligand 4 could also be obtained selectively by changing the reaction stoichiometry to 1 : 1. SalenH21 was explored for the one-pot two-step synthesis of metal complexes. In particular, after in situ formation of the ligand by ball milling, metal salts (ZnO, Ni(OAc)2·4H2O or Cu(OAc)2·H2O) were added directly to the jar and milling continued for a further 30 minutes. Small amounts of methanol (0.4–1.1 mol equivalents) were needed for these reactions to run to completion. The corresponding metal complexes [M(salen)] (M = Zn, 6; Ni, 7; or Cu, 8) were thus obtained quantitatively after 30 minutes in hydrated form, and could be heated briefly to give analytically pure dehydrated products. The all-at-once ‘tandem’ synthesis of [Zn(salen)] 6 was also explored by milling ZnO, ethylene diamine and salicylaldehyde together in the appropriate mole ratio for 60 minutes. This approach also gave the target complex selectively with no solvent needing to be added. Overall, these syntheses were found to be highly efficient in terms of time and the in avoidance of bulk solvent both during the reaction and for the isolation of intermediates. The work demonstrates the applicability of mechanochemical synthesis to one-pot multi-step strategies.

Mechanochemistry provides a method to reduce or eliminate the use of solvents by carrying out reactions through the grinding of neat reagents. Until recently a significant drawback of this form of synthesis has been the limited ability to scale up. However, it has been shown that twin screw extrusion (TSE) may overcome this problem as demonstrated in the continuous synthesis of co-crystals, Metal Organic Frameworks (MOFs) and Deep Eutectic Solvents (DES), in multi kg h−1 quantities. TSE has provided a means to carry out mechanochemical synthesis in a continuous, large scale and efficient fashion, which is adaptable to a manufacturing process. Herein, we highlight the potential of this technique for organic synthesis by reporting four condensation reactions, the Knoevenagel condensation, imine formation, aldol reaction and the Michael addition, to produce analytically pure products, most of which did not require any post synthetic purification or isolation. Each reaction was carried out in the absence of solvents and the water byproduct was conveniently removed as water vapour during the extrusion process due to the elevated temperatures used. Furthermore, the Knoevenagel condensation has been studied in detail to gain insight into the mechanism by which these mechanochemical reactions proceed. The results point to effective wetting of one reactant by another as being critical for these reactions to occur under these reaction conditions.

Porous liquids are a new class of material that could have applications in areas such as gas separation and homogeneous catalysis. Here we use a combination of measurement techniques, molecular simulations, and control experiments to advance the quantitative understanding of these liquids. In particular, we show that the cage cavities remain unoccupied in the absence of a suitable guest, and that the liquids can adsorb large quantities of gas, with gas occupancy in the cages as high as 72% and 74% for Xe and SF6, respectively. Gases can be reversibly loaded and released by using non-chemical triggers such as sonication, suggesting potential for gas separation schemes. Diffusion NMR experiments show that gases are in dynamic equilibrium between a bound and unbound state in the cage cavities, in agreement with recent simulations for related porous liquids. Comparison with gas adsorption in porous organic cage solids suggests that porous liquids have similar gas binding affinities, and that the physical properties of the cage molecule are translated into the liquid state. By contrast, some physical properties are different: for example, solid homochiral porous cages show enantioselectivity for chiral aromatic alcohols, whereas the equivalent homochiral porous liquids do not. This can be attributed to a loss of supramolecular organisation in the isotropic porous liquid.

The selective catalytic reduction (SCR) of NOx in the presence of different reducing agents over Ag/Al2O3 prepared by wet impregnation was investigated by probing catalyst activity and using NMR relaxation time analysis to probe the strength of surface interaction of the various reducing agent species and water. The results reveal that the strength of surface interaction of the reducing agent relative to water, the latter present in engine exhausts as a fuel combustion product and, in addition, produced during the SCR reaction, plays an important role in determining catalyst performance. Reducing agents with weak strength of interaction with the catalyst surface, such as hydrocarbons, show poorer catalytic performance than reducing agents with a higher strength of interaction, such as alcohols. This is attributed to the greater ability of oxygenated species to compete with water in terms of surface interaction with the catalyst surface, hence reducing the inhibiting effect of water molecules blocking catalyst sites. The results support the observations of earlier work in that the light off-temperature and maximum NOx conversion and temperature at which that occurs are sensitive to the reducing agent present during reaction, and the proposal that improved catalyst performance is caused by increased adsorption strength of the reducing agent, relative to water, at the catalyst surface. Importantly, the NMR relaxation time analysis approach to characterising the strength of adsorption more readily describes the trends in catalytic behaviour than does a straightforward consideration of the polarity (i.e., relative permittivity) of the reducing agents studied here. In summary, this paper describes a simple approach to characterising the interaction energy of water and reducing agent so as to aid the selection of reducing agent and catalyst to be used in SCR conversions.

Crystals have been made that undergo reactions when compressed. Computational simulations of these processes provide much-needed atomic-level insight into the mechanisms of mechanically induced reactions. Crystals have been made that undergo reactions when compressed. Computational simulations of these processes provide much-needed atomic-level insight into the mechanisms of mechanically induced reactions.

The aluminum complex Alq3 (q = 8-hydroxyquinolinate), which has important applications in organic light-emitting diode materials, is shown to be readily synthesized as a pure phase under solvent-free mechanochemical conditions from Al(OAc)2OH and 8-hydroxyquinoline by ball milling. The initial product of the mechanochemical synthesis is a novel acetic acid solvate of Alq3, and the α polymorph of Alq3 is obtained on subsequent heating/desolvation of this phase. The structure of the mechanochemically prepared acetic acid solvate of Alq3 has been determined directly from powder X-ray diffraction data and is shown to be a different polymorph from the corresponding acetic acid solvate prepared by solution-state crystallization of Alq3 from acetic acid. Significantly, the mechanochemical synthesis of Alq3 is shown to be fully scalable across two orders of magnitude from 0.5 to 50 g scale. The Alq3 sample obtained from the solvent-free mechanochemical synthesis is analytically pure and exhibits identical photolu...

A general method to prepare organic–inorganic hybrid aerogels has been presented. A series of organic–inorganic hybrid aerogels were successfully produced from 3d trivalent transition metals (Cr3+, Fe3+) and bridging carboxylic acids. Gelation of the Cr(III) gels was achieved by heating the precursor solution to temperatures above 80 °C, which is in sharp contrast to usual supramolecular gels. Among a range of ligands used, highly porous aerogels could be prepared from rigid carboxylate, e.g.1,4-benzenedicarboxylate and 1,3,5-benzenetricarboxylate. The porous aerogels can be described as a coherent, rigid spongy network of continuous nanometre-sized particles, which is significantly different from the usual fibrous network of supramolecular gels. The aerogels have tunable porous structures with micro- and mesoporosity depending on their reactant concentrations. Their surface areas, pore volumes, and average pore sizes were analysed by using nitrogen sorption, and the accessibility of the pores to bulky molecules was also evaluated. It represents a strategy to prepare hybrid materials with large porosity utilising structurally simple building blocks as precursors.

Low-temperature (

Macroporous sponge-like gelatin-fibrinogen (Gl-Fg) scaffolds cross-linked with different concentrations (0.05-0.5%) of glutaraldehyde (GA) were produced using cryogelation technology, which allows for the preparation of highly porous scaffolds without compromising their mechanical properties, and is a more cost-efficient process than freeze-drying. The produced Gl-Fg-GA(X) scaffolds had a uniform interconnected open porous structure with a porosity of up to 90-92% and a pore size distribution of 10-120 microm. All of the obtained cryogels were elastic and mechanically stable, except for the Gl-Fg-GA(0.05) scaffolds. Swelling kinetics and degradation rate, but not the porous structure of the cryogels, were strongly dependent on the degree of cross-linking. A ten-fold increase in the degree of cross-linking resulted in an almost 80-fold decrease in the rate of degradation in a solution of protease. Cryogels were seeded with primary dermal fibroblasts and the densities observed on the surface, plus the expression levels of collagen types I and III observed 5 days post-seeding, were similar to those observed on a control dermal substitute material, Integra. Fibroblast proliferation and migration within the scaffolds were relative to the GA content. Glucose consumption rate was 3-fold higher on Gl-Fg-GA(0.1) than on Gl-Fg-GA(0.5) cryogels 10 days post-seeding. An enhanced cell motility on cryogels with reducing GA crosslinking was obtained after long time culture. Particularly marked cell infiltration was seen in gels using 0.1% GA as a crosslinker. The scaffold started to disintegrate after 42 days of in vitro culturing. The described in vitro studies demonstrated good potential of Gl-Fg-GA(0.1) scaffolds as matrices for wound healing.

Situations where normal autografts cannot be used to replace damaged skin often lead to a greater risk of mortality, prolonged hospital stay and increased expenditure for the National Health Service. There is a substantial need for tissue-engineered skin bioconstructs and research is active in this field. Significant progress has been made over the years in the development and clinical use of bioengineered components of the various skin layers. Off-the-shelf availability of such constructs, or production of sufficient quantities of biological materials to aid rapid wound closure, are often the only means to help patients with major skin loss. The aim of this review is to describe those materials already commercially available for clinical use as well as to give a short insight to those under development. It seeks to provide skin scientists/tissue engineers with the information required to not only developin vitromodels of skin, but to move closer to achieving the ultimate goal of an off-the-shelf, complete full-thickness skin replacement.

The coordination of olefins to square-planar Pd(II) and Pt(II) complexes containing 2,9-dimethylphenanthroline ( L1) often involves a change of color associated with a change of geometry at the metal center. In order to obtain suitable colorimetric detectors for ethylene gas, a series of new Pd(II) and Pt(II) compounds with a range of 2,9-disubstituted phenanthroline ligands [2,9-di- n-butyl-1,10-phenanthroline ( L2), 2,9-di- s-butyl-1,10-phenanthroline ( L3), 2,9-diphenyl-1,10-phenanthroline ( L4), and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine, L5)] have been prepared and their reactivity toward ethylene investigated both in solution and after depositing the detector compounds on a variety of solid supports. The Pd(II) complex [PdCl 2( L2)] supported on silica undergoes a clear color change upon exposure to ethylene, while remaining stable toward air and water, and forms the basis for new simple colorimetric detectors with potential applications in ethylene pipe-leak detection and the monitoring of fruit ripening. Encouragingly, the detector is able to discriminate between fruit at different stages of ripening. The response of the detector to other volatiles was also examined, and specific color changes were also observed upon exposure to aromatic acetylenes. The crystal structures of four new derivatives, including the ethylene-Pt(II) complex [PtCl 2(C 2H 4)( L2)], are also described.

We have investigated a potential test method to monitor changes through possible degradation of a collagen/glycosaminoglycan tissue engineering scaffold in vitro. The method used cyclic voltammetry where the degradation process was measured by determining changes in the apparent diffusion coefficients of thermodynamically reversible couples, ferrocyanide and 1,4-benzoquinone, through the scaffold before and after degradation at low pH and at different temperatures. Scaffold samples were degraded in vitro by exposure to pH 3 for 44 days and also stored in pH 7.4 phosphate saline buffer for one week. Sample temperatures used were 21 degrees C, 37 degrees C and 40 degrees C. The greatest apparent degradation was observed for scaffolds stored at 40 degrees C. Prior to storage, effective diffusion coefficients were 4.4x10(-6) cm2 s(-1) and 2.6x10(-10) cm2 s(-1) for ferrocyanide and 1,4-benzoquinone, respectively. For these respective compounds values changed to 1.2x10(-6) cm2 s(-1) and 1.0x10(-6) cm2 s(-1) after 37 degrees C degradation and 2.6x10(-6) cm2 s(-1) and 5.5x10(-8) cm2 s(-1) after pH 3 degradation.

Degradation of a commercially available collagen-glycosaminoglycan dermal equivalent matrix was studied using electrochemical techniques. Degradation was accelerated by exposure to gamma radiation followed by storage at elevated temperatures or exposure to enzymes. The time-dependent diffusion of a small, electrochemically active, molecular probe, potassium ferrocyanide, through the matrix was monitored via changes in the oxidation peak currents of cyclic voltammograms. These measurements were made using a two-compartment diffusion chamber with the sample positioned well away from the working electrodes and a single-compartment electrode cell where the matrix was in direct contact with the working electrode. The relative merits of these two approaches are considered. Regardless of the approach chosen, amperometry appears well suited to monitoring progressive diffusivity changes through mechanically weak porous structures subject to different solution environments.

The fabrication of buckypaper from unfunctionalised multi-walled carbon nanotubes (MWCNTs) without the aid of surfactants or surface modification techniques is accomplished through a novel and quick frit compression method. The dimensions can be controlled through the size of the syringe housing and the through the mass of carbon nanotubes added. Their thicknesses are typically much larger than surfactant-cast buckypaper and range from 120 μm up to 650 μm; buckypaper with thicknesses larger than 500 μm we call buckydiscs. Buckypaper and buckydiscs are mechanically robust to handle, flexible, stable in solvents and possess larger porosities than Triton-X100 cast buckypaper. They also exhibit a memory effect when bending wetted samples, returning to their former geometry on drying. Buckypaper and buckydiscs were studied by mercury intrusion porosimetry to reveal a defined distribution of mesopores and small macropores that is, along with their density and apparent free volume, dependant on the casting solvent and therefore tuneable. Moreover, the frit compression system also allows control over the 3-dimensional geometry of the buckydiscs during the casting process.

Mechanochemical synthesis has been applied to the rapid synthesis of Deep Eutectic Solvents (DESs), including Reline 200 (choline chloride : urea, 1 : 2), in a continuous flow methodology by Twin Screw Extrusion (TSE). This gave products in higher purity and with Space Time Yields (STYs), four orders of magnitude greater than for batch methods.

Mechanochemistry provides a rapid, efficient route to metal-organic framework Zn-MOF-74 directly from a metal oxide and without bulk solvent. In situ synchrotron X-ray diffraction monitoring of the reaction course reveals two new phases and an unusual step-wise process in which a close-packed intermediate reacts to form the open framework. The reaction can be performed on a gram scale to yield a highly porous material after activation.

The aim of this article is to put forward the novel concept of porous liquids, or, more precisely, liquids with permanent microporosity. In contrast to the small, transient cavities that exist between the molecules of any liquid (here called "extrinsic" porosity), we suggest that a truly microporous liquid could exist if it had empty pores within the molecules of the liquid ("intrinsic" porosity). By using rigid host molecules with restricted access windows, any unwanted occupation of the pores could be prevented (i.e., the pores could be kept empty and available so that the liquid would be genuinely microporous). The liquid could have permanent, well-defined, empty pores capable of molecular recognition when exposed to other species (e.g., gases etc.). We stress that these phases are not the same as simple solutions of host species, in which any pores would normally be occupied by solvent molecules. In microporous liquids, any solvent molecules, if present, would be deliberately sterically excluded from the host cavities, to leave them readily accessible. Microporous liquids would be of considerable fundamental interest. They could combine properties of microporous solids, such as size- and shape-selective sorption and so forth, with the rapid mass transfer, fluidity and fast kinetics of liquids. Some synthetic approaches to these materials are discussed in this article. Also, whilst the overall concept of microporous liquids is new, literature is described which suggests that some examples have arguably already been reported, even if they have not previously been recognised and characterised in such terms.

In 2007 the idea was put forward that, through careful molecular design, it should be possible to synthesize liquids which contain permanent, well-defined molecule-sized cavities (pores). Such "porous liquids" could be a kind of liquid zeolite, or liquid MOF (metal-organic framework), exhibiting the size and shape-selective sorption (or dissolution) associated with microporous solids as well as the fluidity of liquids - a new and potentially useful combination of properties. However, these materials remained essentially hypothetical until recently. In 2014 and 2015 three papers were published which describe convincing examples of porous liquids, and studies have shown that they do exhibit some remarkable properties, such as very fast gas diffusion and high gas solubilities. The examples reported so far are almost certainly only the tip of the iceberg. Now that porous liquids are 'real', a new area of materials science may open up, with clear potential for long-term applications in chemical processes.