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Developing structure-performance relationships with the underlying goal of optimizing known zeolite catalysts involves the manipulation of their physicochemical properties. Here, we systematically assessed the impact of mesoscopic gradients in acid site concentration, which has received little attention in the design of zeolite catalysts for hydrocarbon upgrading. A series of core-shell MEL-type zeolites were synthesized with catalytically active ZSM-11 cores and passivated silicalite-2 shells of varying thickness. Our findings revealed that ZSM-11@silicalite-2 particles with ultrathin shells (

Long-term catheterised individuals are at significant risk of developing catheter-associated urinary tract infections (CAUTIs), with up to 50% of patients experiencing recurrent episodes of catheter encrustation and blockage. Catheter blockage is a result of accumulation of carbonate apatite and struvite formed upon precipitation of ions within urine due to an infection-induced rise in pH. The aim of this study was to investigate the antimicrobial and anti-encrustation activities of tetrasodium ethylenediaminetetraacetic acid (tEDTA) to evaluate its potential efficacy in preventing CAUTIs and catheter blockages. The antimicrobial activity of tEDTA against uropathogens was assessed using time kill assays performed in artificial urine (AU). Crystallisation studies and in vitro bladder model assays were conducted to investigate the effect of tEDTA on struvite crystallisation and catheter blockage. tEDTA displayed bacteriostatic activity against Proteus mirabilis and prevented precipitation of ions in the AU. Crystallisation studies confirmed tEDTA inhibits struvite nucleation and growth via Mg2+ chelation with 7.63 mM tEDTA, equimolar to the concentration of divalent cations in AU, preventing the formation of crystalline deposits and blockage of Foley catheters for $168 h. The promising chelating abilities of low tEDTA concentrations could be exploited to inhibit encrustation and blockage of indwelling catheters. The fundamental research presented will inform our future development of an effective tEDTA-eluting catheter coating aimed at preventing catheter encrustation.

Given the strong influence of surface structure on the reactivity of heterogeneous catalysts, understanding the mechanisms that control crystal morphology is an important component of designing catalytic materials with targeted shape and functionality. Herein, we employ density functional theory to examine the impact of growth media on NiO crystal faceting in line with experimental findings, showing that molten-salt synthesis in alkali chlorides (KCl, LiCl, and NaCl) imposes shape selectivity on NiO particles. We find that the production of NiO octahedra is attributed to the dissociative adsorption of H2 O, whereas the formation of trapezohedral particles is associated with the control of the growth kinetics exerted by ordered salt structures on high-index facets. To our knowledge, this is the first observation that growth inhibition of metal-oxide facets occurs by a localized ordering of molten salts at the crystal-solvent interface. These findings provide new molecular-level insight on kinetics and thermodynamics of molten-salt synthesis as a predictive route to shape-engineer metal-oxide crystals.

Synthesis of a pentasil‐type zeolite with ultra‐small few‐unit‐cell crystalline domains, which we call FDP (few‐unit‐cell crystalline domain pentasil), is reported. FDP is made using bis‐1,5(tributyl ammonium) pentamethylene cations as structure directing agent (SDA). This di‐quaternary ammonium SDA combines butyl ammonium, in place of the one commonly used for MFI synthesis, propyl ammonium, and a five‐carbon nitrogen‐connecting chain, in place of the six‐carbon connecting chain SDAs that are known to fit well within the MFI pores. X‐ray diffraction analysis and electron microscopy imaging of FDP indicate ca. 10 nm crystalline domains organized in hierarchical micro‐/meso‐porous aggregates exhibiting mesoscopic order with an aggregate particle size up to ca. 5 μm. Al and Sn can be incorporated into the FDP zeolite framework to produce active and selective methanol‐to‐hydrocarbon and glucose isomerization catalysts, respectively., A simple di‐quaternary ammonium cation was used as structure‐directing agent to prepare few‐unit‐cell (ca. 10 nm) MFI type zeolite catalysts and adsorbents with a wide range of composition (pure silica, aluminosilicate and stannosilicate). The SDA design was selected based on simple heuristic arguments regarding contributions of its structural elements to early crystal growth characteristics of MFI.

The preparation of metastable zeolites is often restricted to a limited range of synthesis conditions, which is exemplified in commercial syntheses lacking organics to stabilize the crystal structure. In the absence of an organic structure-directing agent, interzeolite transformation is a common phenomenon that can lead to undesirable products or impurities. Many studies have investigated the substitution of Si and Al in zeolite frameworks with alternative elements (heteroatoms) as a means of tailoring the properties of zeolites; however, relatively few studies have systematically explored the impact of heteroatoms on interzeolite transformations and their concomitant effects on zeolite crystallization. In this study, we examine methods to prepare isostructures of faujasite (FAU), which is one of the most commercially relevant zeolites and also a thermodynamically metastable structure. A survey of multivalent elements revealed that zinc is capable of stabilizing FAU at high temperatures and inhibiting its frequent transformation to zeolite gismondine (GIS). Using combined experimental and computational studies, we show that zinc alters the chemical nature of growth mixtures by sequestering silicates. Zinc heteroatoms incorporate in the FAU framework with a loading-dependent coordination. Our collective findings provide an improved understanding of driving forces for the FAU-to-GIS interzeolite transformation where we observe that heteroatoms (e.g., zinc) can stabilize zeolite FAU over a broad range of synthesis conditions. Given the growing interest in heteroatom-substituted zeolites, this approach to preparing zinc-containing FAU may prove applicable to a broader range of zeolite structures.

Zeolite crystallization often requires the presence of an organic structure-directing agent (SDA) to facilitate the formation of nanoporous cages and channels. Among the limited number of zeolites ...

This mini-review provides an overview of the current state of acid site control in zeolite catalysts, including methods of synthesis, advanced characterization, and measured effects of acid properties (speciation, concentration, proximity, siting, and spatial distribution) on a variety of commercially-relevant reactions. The diversity of aluminum species is described with respect to their location at specific sites in zeolite crystals as well as mesoscopic gradients in elemental composition that give rise to zoned or core-shell architectures. Challenges in the identification of acid siting are highlighted within the context of trial-and-error synthesis methods for a range of aluminosilicate frameworks, which hinder a priori design of catalysts, and limitations in techniques to suitably characterize active sites. Emphasis is also placed on knowledge gaps in zeolite catalysis wherein broad development of structure-performance relationships relies on future advancement of synthesis and analytical methods in parallel with atomistic modeling.

Bifunctional catalysis in zeolites possessing both Bronsted and Lewis acid sites offers unique opportunities to tailor shape selectivity and enhance catalyst performance. Here, we examine the impact of framework and extra-framework gallium species on enriched aromatics production in zeolite ZSM-5. In this study we compare three distinct methods of preparing Ga-ZSM-5 and reveal direct (single step) synthesis leads to optimal catalysts compared to post-synthesis methods. Using a combination of state-of-the-art characterization, catalyst testing, and density functional theory calculations, we show that Ga Lewis acid sites strongly favor aromatization. Our findings also suggest Ga(framework) - Ga(extra-framework) pairings, which can only be achieved in materials prepared by direct synthesis, are the most energetically favorable sites for reaction pathways leading to aromatics. Calculated acid site exchange energies between extra-framework Ga at framework sites comprised of either Al or Ga reveal a site-specific preference for stabilizing Lewis acids, which is qualitatively consistent with experimental measurements. These findings indicate the possibility of tailoring Lewis acid siting by the placement of Ga heteroatoms at distinct tetrahedral sites in the zeolite framework, which can have a marked impact on catalyst performance relative to conventional H-ZSM-5.

Metal oxides exposing high-index facets are potentially impactful in catalysis and adsorption processes owing to under-coordinated ions and polarities that alter their interfacial properties compared to low-index facets. Here, we report molten-salt syntheses of NiO particles exposing a variety of crystal facets. We show that for a given anion (nitrate or chloride), the alkali cation has a notable impact on the formation of crystals exposing {311}, {611}, {100}, and {111} faces. Based on a parametric analysis of synthesis conditions, we postulate that the crystallization mechanism is governed by the formation of growth units consisting of NiII complexes whose coordination numbers are determined by temperature and the selection of anion (associated to the coordination sphere) and alkali cation (associated with the outer coordination sphere). Notably, our findings reveal that high-index facets are particularly favored in chloride media and are stable under prolonged periods of catalysis and steaming.

Tailoring processes of nucleation and growth to achieve desired material properties is a pervasive challenge in synthetic crystallization. In systems where crystals form via nonclassical pathways, engineering materials often requires the controlled assembly and structural evolution of colloidal precursors. In this study, we examine zeolite SSZ-13 crystallization and show that several polyquaternary amines function as efficient accelerants of nucleation, and, in select cases, tune crystal size by orders of magnitude. Among the additives tested, polydiallyldimethylammonium (PDDA) was found to have the most pronounced impact on the kinetics of SSZ-13 formation, leading to a 4-fold reduction in crystallization time. Our findings also reveal that enhanced nucleation occurs at an optimal PDDA concentration where a combination of light scattering techniques demonstrate these conditions lead to polymer-induced aggregation of amorphous precursors and the promotion of (alumino)silicate precipitation from growth solution. Here, we show that relatively low concentrations of polymer additives can be used in unique ways to dramatically enhance SSZ-13 crystallization rates, thereby improving the overall efficiency of zeolite synthesis. JDR received financial support primarily from BASF Corporation along with additional support from the Welch Foundation (Award E-1794). JGM received financial support from the European Commission through the H2020-MSCA-RISE-2019 program (Award ZEOBIOCHEM – 872102) and the Spanish MINECO and AEI/FEDER, UE through Award RTI2018-099504-B-C21. NL acknowledges the University of Alicante support (Award UATALENTO17-05).

Zeolite crystals can be used as seeds or aluminosilicate sources in syntheses to control polymorphs and/or reduce the quantity of organics used as structure-directing agents. A frequently invoked hypothesis for interzeolite transformations is that zeolites share some underlying similarity in structure, most notably in cases pertaining to organic-free syntheses. Herein, we show for the first time that ZSM-5 (MFI) can be directly obtained from USY (FAU) through an interzeolite transformation between parent-daughter structures lacking common building units in the absence of a structure-directing agent and seeds. We show that interzeolite transformation leads to a crystalline product with fewer defects. Our findings also reveal that ZSM-5 is a metastable intermediate that undergoes further transformation to mordenite (MOR) and quartz. The MFI-to-MOR transition is counter to reported trends for which transformations lead to structures with reduced molar volume. Herein, we propose mechanistic arguments that suggest the driving force for interzeolite transformation is more complex than guidelines posited in the literature.

Unbiased zeolite dissolution removes defects in the structure, enabling retroactive assessment of crystallization history., Zeolite crystal growth mechanisms are not fully elucidated owing to their complexity wherein the formation of a particular zeolite can occur by more than one crystallization pathway. Here, we have conducted time-resolved dissolution experiments of MFI-type zeolite crystals in ammonium fluoride medium where detailed structural analysis allowed us to extrapolate and elucidate the possible mechanism of nucleation and crystal growth. A combination of electron and scanning probe microscopy shows that dissolution initiates preferentially at lattice defects and progressively removes defect zones to reveal a mosaic structure of crystalline domains within each zeolite crystal. This mosaic architecture evolves during the growth process, reflecting the changing conditions of zeolite formation that can be retroactively assessed during zeolite crystal dissolution. Moreover, a more general implication of this study is the establishment that dissolution can be used successfully as an ex situ technique to uncover details about crystal growth features inaccessible by other methods.

Zeolite crystallization predominantly occurs by nonclassical pathways involving the attachment of complex (alumino)silicate precursors to crystal surfaces, yet recurrent images of fully crystalline materials with layered surfaces are evidence of classical growth by molecule attachment. Here we use in situ atomic force microscopy to monitor three distinct mechanisms of two-dimensional (2D) growth of zeolite A where we show that layer nucleation from surface defects is the most common pathway. Direct observation of defects was made possible by the identification of conditions promoting layered growth, which correlates to the use of sodium as an inorganic structure-directing agent, whereas its replacement with an organic results in a nonclassical mode of growth that obscures 2D layers and markedly slows the rate of crystallization. In situ measurements of layered growth reveal that undissolved silica nanoparticles in the synthesis medium can incorporate into advancing steps on crystal surfaces to generate defects (i.e., amorphous silica occlusions) that largely go undetected in literature. Nanoparticle occlusion in natural and synthetic crystals is a topic of wide-ranging interest owing to its relevance in fields spanning from biomineralization to the rational design of functional nanocomposites. In this study, we provide unprecedented insight into zeolite surface growth by molecule addition through time-resolved microscopy that directly captures the occlusion of silica nanoparticles and highlights the prevalent role of defects in zeolite crystallization.

Polyprotic acids often serve as effective regulators of inorganic crystallization in natural, biological, and synthetic systems. These molecules or macromolecules can function as efficient modifiers that either inhibit or promote crystal growth. Few studies report potent inhibitors of crystal nucleation owing to the presumed challenges of hindering these stochastic events; however, in this study, we have identified polyphosphates that operate as potent inhibitors of both nucleation and crystal growth of the natural mineral struvite (MgNH4PO4·6H2O), which is a common component of scale in commercial and physiological processes (e.g., water purification and kidney disease). Systematic investigation of linear and cyclic polyphosphates of varying molecular weight reveal that micromolar concentrations of three modifiers, hexametaphosphate, polyphosphate type 45, and phytic acid, lead to suppressed struvite nucleation. Combined studies of struvite growth at the macroscopic level using microfluidics to track anisotropic rates of crystallization and at the molecular level using in situ atomic force microscopy (AFM) to monitor layered growth of crystal surfaces collectively reveal that these modifiers are also capable of fully suppressing crystal growth via their affinity to interact with all principal crystal facets. Time-resolved AFM images of the (101) surface at varying polyphosphate concentrations reveal a unique mode of crystal growth inhibition, wherein surfaces become laden with an amorphous layer that leads to roughened interfaces and growth succession through dynamic sequences that are not commonly witnessed for other minerals. It is also observed under certain conditions that inhibitors can induce significant changes in crystal morphology, leading to exquisite leaflike hierarchical structures. The discovery of potent inhibitors of struvite formation that operate by unparalleled dual modes of action capable of suppressing both nucleation and crystal growth has potential implications for their use in the prevention of commercial scale in water purification as well as in the treatment of kidney stones. Moreover, the fundamental mechanisms of polyphosphates identified in this study may prove to be relevant for other inorganic crystals given the ubiquitous use of inhibitors in processes spanning from biomineralization to crystal engineering.

Reaction-transport formalisms show that the effects of crystallite size, H+ density, and Si speciation of HSAPO-34 on catalyst lifetime and selectivity in methanol-to-olefins catalysis are all manifestations of diffusional constraints. Both structural catalyst properties—i.e., crystallite size and H+ density—and intrinsic kinetic constants (per H+)—regulated, in silicoaluminophosphates, by Si speciation—affect the severity of these diffusional restrictions. Methanol-to-olefins catalysis on HSAPO-34 occurs by a complex network of autocatalytic reactions in which temporal gradients persist along with spatial gradients inherent to continuous-flow, fixed-bed reactors. Invocation of reaction rates in the interpretation of lifetime and selectivity trends in such systems requires defined quantities averaged in both time and space because measured observables conflate instantaneous reaction rates with spatial and temporal gradients. Quantities defined herein, i.e., total turnovers and cumulative selectivity, provide such rigorous assessments of lifetime and selectivity that permit causative correlation between rates of reactions within the complex network of autocatalytic reactions and material properties of HSAPO-34. Total turnovers decreases with increasing diffusional constraints because dehydrocyclization reactions experience stronger diffusional constraints than olefins methylation, aromatics dealkylation, and methanol transfer hydrogenation. Cumulative selectivity to paraffins increases with increasing diffusional constraints because transfer hydrogenation reactions of methanol, ethylene, and propylene experience stronger diffusional constraints than all other reactions within the complex reaction network. The approaches detailed herein codify the chemical and physical origins of trends in process outcomes with system variables for reaction systems characterized by complex reaction networks and prevailing spatial and temporal concentration gradients.

Calcified minerals in biogenic materials often play a utilitarian role, such as structural supports in bone, teeth, and shells, where the crystals are arranged in well-ordered arrays (1, 2). The ability of organisms to produce single crystalline scaffolds and hierarchical architectures with unique features, such as bent or spheroidal shapes, has long fascinated scientists. The mechanisms of biomineral nucleation and growth are complex and not fully understood, while the ability to mimic these processes in vitro has proven challenging. Much attention has been given to studying the skeletal sections of sea urchins and other organisms (e.g., mollusks, echinoderms, calcisponges, and corals) that contain curved surfaces and various convoluted shapes (3). From numerous studies of these materials, which are predominantly composed of calcium carbonate minerals, it has become evident that crystallization originates from the initial formation of amorphous calcium carbonate (ACC) (4, 5). The pathways by which ACC transforms into crystalline CaCO3 polymorphs has been a topic of ongoing investigation, although many fundamental details remain elusive. In PNAS, Liu et al. (6) report the time-resolved evolution of ACC to crystalline calcium carbonate using in situ transmission electron microscopy to show that the presence of inorganic ions leads to the direct transformation of the amorphous phase to calcite, all the while preserving the morphology of the original precursor. ACC has become a recognized and frequently investigated form of calcium carbonate owing to its importance in biomineralization. Six additional crystalline forms of calcium carbonate (1) include calcite, aragonite, vaterite, … [↵][1]1Email: jrimer{at}central.uh.edu. [1]: #xref-corresp-1-1

The assembly and structural evolution of amorphous precursors during zeolite crystallization is an important area of interest owing to their putative roles in the nucleation and growth of aluminosilicate microporous materials. Precursors range in complexity from oligomeric molecules and colloidal particles to gels comprised of heterogeneous silica and alumina domains. The physical state of precursors in most zeolite syntheses is generally not well understood; however, it is evident that the physicochemical properties of precursors depend on a wide range of conditions that include (but are not limited to) the selection of reagents, the composition of growth mixtures, the methods of preparation, and the use of inorganic and/or organic structure-directing agents. The fact that precursors evolve in size, shape, and/or microstructure during the course of nucleation and potentially throughout crystallization leads to questions pertaining to their mode of action in the formation of zeolites. This also highlights...

Crystal engineering relies upon the ability to predictively control intermolecular interactions during the assembly of crystalline materials in a manner that leads to a desired (and predetermined) set of properties. Economics, scalability, and ease of design must be leveraged with techniques that manipulate the thermodynamics and kinetics of crystal nucleation and growth. It is often challenging to exact simultaneous control over multiple physicochemical properties, such as crystal size, habit, chirality, polymorph, and composition. Engineered materials often rely upon postsynthesis (top-down) processes to introduce properties that would otherwise be challenging to attain through direct (bottom-up) approaches. We discuss the application of crystal engineering to heterogeneous catalysts with a focus on four general themes: ( a) tailored nanocrystal size, ( b) controlled environments surrounding active sites, ( c) tuned morphology with well-defined facets, and ( d) hierarchical materials with disparate pore size and active site distributions. We focus on nonporous materials, including metals and metal oxides, and two classes of porous materials: zeolites and metal organic frameworks. We review novel synthesis methods involving synergistic experimental and computational design approaches, the challenges facing catalyst development, and opportunities for future advancement in crystal engineering.

Exothermic heat effects are a crucial factor in determining the performance and stability of catalysts for the oxidative coupling of methane (OCM). Fixed bed temperature rise, steady state multiplicity, and catalyst durability are investigated over a range of feed conditions for the mixed metal oxides Cs/Sr/MgO, Cs/Ba/MgO, Cs/Sr/La2O3, and Na2WO4-Mn/SiO2. A comparison with previous studies on doped metal oxides catalysts for OCM clearly indicates that doping not only improves the performance but also significantly improves the catalyst stability. We experimentally demonstrate for the first time hysteresis behavior for Cs/Sr/La2O3 powder catalyst. Our results show that the catalyst stability depends on the magnitude of temperature rise in the catalyst bed. At a lower space velocity of 3,600 cc/h/g, the catalysts exhibit moderate temperature rise (

Developing new zeolite catalysts for (petro)chemical applications is nontrivial owing to challenges that include the identification of commercially-viable syntheses. The vast majority of syntheses require the use of an organic structure-directing agent (OSDA), which has economic and environmental shortcomings. In the search for alternative zeolites to common industrial catalysts, such as ZSM-5 (MFI), a promising candidate is ZSM-11 (MEL), a close structural analogue of MFI. ZSM-11 is comprised of 3-dimensional straight channels that have less diffusion limitations than MFI. Side-by-side comparisons of ZSM-11 and ZSM-5 catalysts reveal the former exhibits significantly longer time-on-stream lifetime in many reactions; however, there are several difficulties associated with the preparation of ZSM-11, which include the ability to identify inexpensive OSDAs that produce small crystals in high yield. Here, we examine ZSM-11 synthesis using 1,8-diaminooctane (DAO), which produces ZSM-11 crystals with sizes of ca. 300 nm. We demonstrate that the use of MEL seeds allows for an order of magnitude reduction in the quantity of DAO without sacrificing crystal purity or yield (80 %). Catalytic tests using methanol to hydrocarbons as a representative reaction show that H-ZSM-11 lifetime and selectivity are similar for samples prepared with and without seeds. Collectively our findings highlight an efficient method to produce ZSM-11 as a potential alternative to ZSM-5 for catalytic applications.

We report the most siliceous FAU-type zeolite, HOU-3, prepared via a one-step organic-free synthesis route. Computational studies indicate that it is thermodynamically feasible to synthesize FAU with SAR=2-7, though kinetic factors seemingly impose a more restricted upper limit for HOU-3 (SAR≈3). Our findings suggest that a slow rate of crystallization and/or low concentration of Na+ ions in HOU-3 growth mixtures facilitate Si incorporation into the framework. Interestingly, Q4 (nAl) Si speciation measured by solid-state NMR can only be modeled with a few combinations of Al positioning at tetrahedral sites in the crystal unit cell, indicating the distribution of Si(-O-Si)4-n (-O-Al)n species is spatially biased as opposed to being random. Achieving higher SAR is desirable for improved zeolite (hydro)thermal stability and enhanced catalytic performance, which we demonstrate in benchmark tests that show HOU-3 is superior to commercial zeolite Y.

The shape selectivity of ZSM-5 (MFI type) catalysts is ideal for the production of C6–C8 aromatics. Developing high-performance zeolite catalysts with improved selectivity to aromatics, particularly from diversified (non-petroleum) feedstocks, has broad commercial appeal. Non-oxidative coupling (NOC) of ethylene was examined over Ag-ZSM-5 catalysts at 400 °C and shows that Ag+ sites promote dehydroaromatization with enhanced selectivity to toluene and xylenes. Metal exchange of H-ZSM-5 results in Ag zoning wherein Ag+ site density is higher on the exterior of ZSM-5 particles. Catalyst performance was characterized with varying Ag loading as well as the use of methane co-feed. Aromatic selectivity is about 60 % on Ag-ZSM-5 compared to 20 % on H-ZSM-5, which is qualitatively consistent with density functional theory (DFT) showing that ethylene forms strong complexes with Ag+ (Lewis acid) sites. DFT calculations also reveal that ethylene activation on H+ (Bronsted acid) sites is more energetically favorable, and likely constitutes the first mechanistic step in ethylene-to-liquids (ETL) reactions. Ag-ZSM-5 is thus identified as an effective catalyst for low-temperature ETL reactions that has the potential to outperform conventional metal-exchanged zeolites.

The effects of methanol space velocity and inlet methanol partial pressure on lifetime and selectivity of methanol-to-olefins catalysis are examined and interpreted to elucidate reaction parameters and propose intermediates and reactions relevant to catalyst deactivation. The propensity of active centers in HSSZ-13 to turn over for methanol-to-olefins catalysis increases when the methanol partial pressure local to organic co-catalysts confined within the inorganic chabazite cages is lower either by decreasing methanol space velocity or inlet methanol partial pressure. High initial methane selectivity reveals methanol disproportionation, to methane and formaldehyde, a primary reaction, and continual methane formation implicates persistent participation of methanol in bimolecular hydrogen transfer reactions throughout the catalyst lifetime. Methane selectivity correlates positively with inlet methanol partial pressure reflecting enhanced relative rates of formaldehyde formation with increasing methanol partial pressure. Subsequent alkylation reactions of olefins- and aromatics-based C C chain growth carriers by formaldehyde accelerate the relative rates of hydrogen transfer and proliferate, apparently, the precursors mediating the transformation of active hydrocarbon pool participants to those inducing catalyst deactivation.

Ubiquitous processes in nature and the industry exploit crystallization from multicomponent environments1–5; however, laboratory efforts have focused on the crystallization of pure solutes6,7 and the effects of single growth modifiers8,9. Here we examine the molecular mechanisms employed by pairs of inhibitors in blocking the crystallization of haematin, which is a model organic compound with relevance to the physiology of malaria parasites10,11. We use a combination of scanning probe microscopy and molecular modelling to demonstrate that inhibitor pairs, whose constituents adopt distinct mechanisms of haematin growth inhibition, kink blocking and step pinning12,13, exhibit both synergistic and antagonistic cooperativity depending on the inhibitor combination and applied concentrations. Synergism between two crystal growth modifiers is expected, but the antagonistic cooperativity of haematin inhibitors is not reflected in current crystal growth models. We demonstrate that kink blockers reduce the line tension of step edges, which facilitates both the nucleation of crystal layers and step propagation through the gates created by step pinners. The molecular viewpoint on cooperativity between crystallization modifiers provides guidance on the pairing of modifiers in the synthesis of crystalline materials. The proposed mechanisms indicate strategies to understand and control crystallization in both natural and engineered systems, which occurs in complex multicomponent media1–3,8,9. In a broader context, our results highlight the complexity of crystal–modifier interactions mediated by the structure and dynamics of the crystal interface., SCOPUS: ar.j, info:eu-repo/semantics/published

Differentiating mechanisms of zeolite crystallization is challenging owing to the vast number of species in growth solutions. The presence of amorphous colloidal particles is ubiquitous in many zeolite syntheses, and has led to extensive efforts to understand the driving force(s) for their self-assembly and putative roles in processes of nucleation and growth. In this study, we use a combination of in situ scanning probe microscopy, particle dissolution measurements, and colloidal stability assays to elucidate the degree to which silica nanoparticles evolve in their structure during the early stages of silicalite-1 synthesis. We show how changes in precursor structure are mediated by the presence of organics, and demonstrate how these changes lead to significant differences in precursor-crystal interactions that alter preferred modes of crystal growth. Our findings provide guidelines for selectively controlling silicalite-1 growth by particle attachment or monomer addition, thus allowing for the manipulation of anisotropic rates of crystallization. In doing so, we also address a longstanding question regarding what factors are at our disposal to switch from a nonclassical to classical mechanism.

Ubiquitous processes in nature and the industry exploit crystallization from multicomponent environments

The formation of crystal aggregates, one of the critical processes in kidney stone pathogenesis, involves interactions between crystals (predominantly calcium oxalate monohydrate, COM) and urinary constituents (e.g., proteins), which serve as an adhesive "glue" between crystals in stones. To develop a better understanding of the protein-crystal interactions that lead to crystal aggregation, we have measured the effect of model proteins on bulk COM crystal properties as well as their adsorption on crystal surfaces using three synthetic polyanions: poly(aspartic acid) (polyD), poly(glutamic acid) (polyE), and poly(acrylic acid) (polyAA). These anionic macromolecules reduced the amount of COM crystal aggregation in bulk solution to an extent similar to that observed for mixture of proteins from normal urine, with little difference between the polymers. In contrast, the polymers exhibited differences in measures of COM crystal growth. Polycations such as poly(arginine) (polyR) and poly(lysine) (polyK) reduced aggregation weakly and exerted negligible effects on crystal growth. All polyions were found to associate with COM crystal surfaces, as evidenced by changes in the zeta potential of COM crystals in electrophoretic mobility measurements. On the other hand, COM aggregation and possibly growth can be promoted by many binary mixtures of polycations and polyanions, which appeared to be mediated by polymer aggregate formation rather than loss of crystal charge stabilization. Similarly, crystal aggregation promotion behavior can be driven by forming aggregates of weakly charged polyanions, like Tamm-Horsfall protein, suggesting that polymer (protein) aggregation may play a critical role in stone formation. Sensitivity of polyanion-COM crystal surface interactions to the chemical composition of polymer side groups were demonstrated by large differences in crystal aggregation behavior between polyD and polyE, which correlated with atomic force microscopy (AFM) measurements of growth inhibition on various COM surfaces and chemical force microscopy (CFM) measurements of unbinding forces between COM crystal surfaces and AFM tips decorated with either carboxylate or amidinium moieties (mimicking polyanion and polyR side chains, respectively). The lack of strong interaction for polyE at the COM (100) surface compared to polyD appeared to be the critical difference. Finally, the simultaneous presence of polyanions and polycations appeared to alter the ability of polycations to mediate unbinding forces in CFM and promote crystal growth. In summary, polyanions strongly associated with COM surfaces and influenced crystallization, while polycations did not, though important differences were observed based on the physicochemical properties of polyanions. Observations suggest that COM aggregation with both polyanion-polycation mixtures and weakly charged polyanions is promoted by polymer aggregate formation, which plays a critical role in bridging crystal surfaces.

The use of growth modifiers in natural, biological, and synthetic crystallization is a ubiquitous strategy for controlling growth and achieving desired physicochemical properties. For crystals that grow classically (i.e., monomer-by-monomer addition), theories of crystallization are well established and the field of growth modification is rather mature, although many questions remain regarding the molecular driving forces of modifier–crystal interactions. A new frontier in crystallization is the application of classical methods to tailor materials that grow nonclassically (i.e., growth by the addition of species more complex than monomers). A recent surge of interest and activity in this field has been driven by mounting evidence of both inorganic and organic materials that grow via nonclassical pathways. In these systems, the challenge of elucidating the mechanism(s) of crystallization is underscored by a diversity of growth units that far outnumber those available for classical routes. In this Perspecti...

Designing zeolites with tunable physicochemical properties can substantially impact their performance in commercial applications, such as adsorption, separations, catalysis, and drug delivery. Zeolite synthesis typically requires an organic structure-directing agent to produce crystals with specific pore topology. Attempts to remove organics from syntheses to achieve commercially viable methods of preparing zeolites often lead to the formation of impurities. Herein, we present organic-free syntheses of two polymorphs of the small-pore zeolite P (GIS), P1 and P2. Using a combination of adsorption measurements and density functional theory calculations, we show that GIS polymorphs are selective adsorbents for H2 O relative to other light gases (e.g., H2 , N2 , CO2 ). Our findings refute prior theoretical studies postulating that GIS-type zeolites are excellent materials for CO2 separation/sequestration. We also show that P2 is significantly more thermally stable than P1, which broadens the operating conditions for GIS-type zeolites in commercial applications and opens new avenues for exploring their potential use in processes such as catalysis.

Malaria is a pervasive disease that affects millions of lives each year in equatorial regions of the world. During the erythrocytic phase of the parasite life cycle, Plasmodium falciparum invades red blood cells, where it catabolizes hemoglobin and sequesters the released toxic heme as innocuous hemozoin crystals. Artemisinin (ART)-class drugs are activated in vivo by newly released heme, which creates a carbon-centered radical that markedly reduces parasite density. Radical damage to parasite lipids and proteins is perceived to be ARTs’ dominant mechanism of action. By contrast, quinoline-class antimalarials inhibit the formation of hemozoin and in this way suppress heme detoxification. Here, we combine malaria parasite assays and scanning probe microscopy of growing β-hematin crystals to elucidate an unexpected mechanism employed by two widely administered antimalarials, ART, and artesunate to subdue the erythrocytic phase of the parasite life cycle. We demonstrate that heme–drug adducts, produced after the radical activation of ARTs and largely believed to be benign bystanders, potently kills P. falciparum at low exogenous concentrations. We show that these adducts inhibit β-hematin crystallization and heme detoxification, a pathway which complements the deleterious effect of radicals generated via parent drug activation. Our findings reveal an irreversible mechanism of heme–ART adduct inhibition of heme crystallization, unique among antimalarials and common crystal growth inhibitors, that opens new avenues for evaluating drug dosing regimens and understanding growing resistance of P. falciparum to ART.

Seed-assisted approaches in zeolite synthesis differ from classical processes in that the seeds tend to dissolve, giving rise to an unknown memory of the parent crystal structure that facilitates the nucleation of the daughter. It has been hypothesized in literature that a shared structural feature, such as a composite building unit, between the parent and the crystals produced from a non-seeded growth solution results in identical parent-daughter framework types. In this study, our findings reveal that this scenario is true in select cases, but often the initial structure formed in seeded syntheses is metastable, resulting in interzeolite transformation(s) with prolonged hydrothermal treatment. In general, the trajectory tends to favor a final structure identical to that obtained by non-seeded growth under identical synthesis conditions. Here, we explore how seed-assisted syntheses impact zeolite properties such as size, morphology, structure, and defects. We observe that the molar composition of the growth mixture and the properties of the seed crystals play a significant role in controlling the kinetics of nucleation and the trajectory of interzeolite transformations. Furthermore, we observe that seeds offer unique routes to achieve small crystal sizes and distinct morphologies in comparison to many conventional syntheses. Advantages of seeding include shorter synthesis time and the ability to reduce or eliminate the need for organic structure-directing agents, thereby providing a facile and efficient route to design zeolites for various industrial applications. The fundamental mechanisms underlying zeolite seed-assisted crystallization are complex and elusive; however, our study provides new insight into these processes and highlights the important role of kinetics in governing parent-daughter (or seed-product) relationships.