Early Onset of Kinetic Roughening due to a Finite Step Width in Hematin Crystallization

The structure of the interface of a growing crystal with its nutrient phase largely determines the growth dynamics. We demonstrate that hematin crystals, crucial for the survival of malaria parasites, transition from faceted to rough growth interfaces at increasing thermodynamic supersaturation Δμ. Contrary to theoretical predictions and previous observations, this transition occurs at moderate values of Δμ. Moreover, surface roughness varies nonmonotonically with Δμ, and the rate constant for rough growth is slower than that resulting from nucleation and spreading of layers. We attribute these unexpected behaviors to the dynamics of step growth dominated by surface diffusion and the loss of identity of nuclei separated by less than the step width w. We put forth a general criterion for the onset of kinetic roughening using w as a critical length scale.National Institutes of Health (U.S.) (Grant 1R21AI126215-01)National Science Foundation (U.S.) (Grant DMR-1710354)United States. National Aeronautics and Space Administration (Grant NNX14AD68G)United States. National Aeronautics and Space Administration (Grant NNX14AE79G)Robert A. Welch Foundation (Grant E-1794

Ultrasmall Zeolite L Crystals Prepared from Highly Interdispersed Alkali‐Silicate Precursors

The preparation of nanosized zeolites is critical for applications where mass‐transport limitations within microporous networks hinder their performance. Often the ability to generate ultrasmall zeolite crystals is dependent upon the use of expensive organics with limited commercial relevance. Herein, we report the generation of zeolite L crystals with uniform sizes less than 30 nm using a facile, organic‐free method. Time‐resolved analysis of precursor assembly and evolution during nonclassical crystallization highlights key differences among silicon sources. Our findings reveal that a homogenous dispersion of potassium ions throughout silicate precursors leads to the formation of a metastable nonporous phase, which undergoes an intercrystalline transformation to zeolite L. The generation of highly interdispersed alkali‐silicate precursors is seemingly critical to enhancing the rate of nucleation and facilitating the formation of ultrasmall crystal.J.D.R. acknowledges support primarily from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0014468. Additional support was provided by the Welch Foundation (Award E-1794). N.L. acknowledges support from the University of Alicante under the project GRE15-07

Ultrasmall Zeolite L Crystals Prepared from Highly Interdispersed Alkali‐Silicate Precursors

The preparation of nanosized zeolites is critical for applications where mass‐transport limitations within microporous networks hinder their performance. Often the ability to generate ultrasmall zeolite crystals is dependent upon the use of expensive organics with limited commercial relevance. Herein, we report the generation of zeolite L crystals with uniform sizes less than 30 nm using a facile, organic‐free method. Time‐resolved analysis of precursor assembly and evolution during nonclassical crystallization highlights key differences among silicon sources. Our findings reveal that a homogenous dispersion of potassium ions throughout silicate precursors leads to the formation of a metastable nonporous phase, which undergoes an intercrystalline transformation to zeolite L. The generation of highly interdispersed alkali‐silicate precursors is seemingly critical to enhancing the rate of nucleation and facilitating the formation of ultrasmall crystal.J.D.R. acknowledges support primarily from the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0014468. Additional support was provided by the Welch Foundation (Award E-1794). N.L. acknowledges support from the University of Alicante under the project GRE15-07

Time-resolved dissolution elucidates the mechanism of zeolite MFI crystallization

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

Diverse Physical States of Amorphous Precursors in Zeolite Sol Gel Syntheses

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 the diversity of species that are present in growth media, thus rendering the topic of zeolite synthesis essentially a black box to those attempting to better understand the fundamental role(s) of precursors. In this Article, we discuss the wide variety of precursors encountered in the synthesis of various framework types, emphasizing their complex physical states and the thermodynamic and kinetic factors that govern their heterogeneity.J.D.R. acknowledges financial support from the National Science Foundation (DMREF Award 1629398), the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0014468, and the Welch Foundation (Award E-1794). N.L. acknowledges support from the University of Alicante under the project GRE15-07. Work done at Argonne and use of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Argonne National Laboratory, were supported by the U.S. Department of Energy under Contract No. DE-AC02-06CH11357

Tautomerism unveils a self-inhibition mechanism of crystallization

Modifiers are commonly used in natural, biological, and synthetic crystallization to tailor the growth of diverse materials. Here, we identify tautomers as a new class of modifiers where the dynamic interconversion between solute and its corresponding tautomer(s) produces native crystal growth inhibitors. The macroscopic and microscopic effects imposed by inhibitor-crystal interactions reveal dual mechanisms of inhibition where tautomer occlusion within crystals that leads to natural bending, tunes elastic modulus, and selectively alters the rate of crystal dissolution. Our study focuses on ammonium urate crystallization and shows that the keto-enol form of urate, which exists as a minor tautomer, is a potent inhibitor that nearly suppresses crystal growth at select solution alkalinity and supersaturation. The generalizability of this phenomenon is demonstrated for two additional tautomers with relevance to biological systems and pharmaceuticals. These findings offer potential routes in crystal engineering to strategically control the mechanical or physicochemical properties of tautomeric materials

Communication and marketing as tools to cultivate the public's health: a proposed "people and places" framework

<p>Abstract</p> <p>Background</p> <p>Communication and marketing are rapidly becoming recognized as core functions, or core competencies, in the field of public health. Although these disciplines have fostered considerable academic inquiry, a coherent sense of precisely how these disciplines can inform the practice of public health has been slower to emerge.</p> <p>Discussion</p> <p>In this article we propose a framework – based on contemporary ecological models of health – to explain how communication and marketing can be used to advance public health objectives. The framework identifies the attributes of people (as individuals, as social networks, and as communities or populations) and places that influence health behaviors and health. Communication, i.e., the provision of information, can be used in a variety of ways to foster beneficial change among both people (e.g., activating social support for smoking cessation among peers) and places (e.g., convincing city officials to ban smoking in public venues). Similarly, marketing, i.e., the development, distribution and promotion of products and services, can be used to foster beneficial change among both people (e.g., by making nicotine replacement therapy more accessible and affordable) and places (e.g., by providing city officials with model anti-tobacco legislation that can be adapted for use in their jurisdiction).</p> <p>Summary</p> <p>Public health agencies that use their communication and marketing resources effectively to support people in making healthful decisions and to foster health-promoting environments have considerable opportunity to advance the public's health, even within the constraints of their current resource base.</p

Time-Resolved Dynamics of Intracrystalline Mesoporosity Generation in USY Zeolite

The treatment of zeolites with surfactants in alkaline media is an effective and versatile technique to impart intracrystalline well-defined mesoporosity in these materials. In this study, the dynamics of surface reconstruction that occurs during the treatment of USY zeolite by surfactant-templating was monitored in situ by atomic force microscopy. The development of surfactant-templated mesoporosity and the concurrent healing of defects that are characteristic of steamed zeolites occur in less than 1 h at room temperature, which emphasizes the low energy barriers needed to reorganize the crystalline structure of this zeolite. This transformation was also followed by X-ray diffraction, N2 adsorption, and transmission electron microscopy analysis of ultramicrotomed samples to confirm that the rapid formation of surfactant-templated mesoporosity and the reconstruction of the zeolite crystals occur not only on the surface of the zeolite but also homogeneously throughout the whole zeolite. This process involves a significant and rapid breaking and re-formation of bonds; however, the zeolite does not dissolve during this process as solid recovery at any given time of the treatment is approximately 100% and the concentration of soluble Si or Al species in the liquid is negligible. Parametric analysis revealed that excessive NaOH leads to the partial transformation of zeolite into an amorphous mesoporous solid, while insufficient quantity of base and/or treatment time can lead to an incomplete mesostructuring of the zeolite, which highlights the importance of judiciously selecting the treatment conditions for every given zeolite.N.L. acknowledges funding from the University of Alicante, through the “Programa de retención y captación de talento” (ref. UATALENTO17-05). J.D.R. acknowledges funding from the Welch Foundation (Award E-1794)

Tailoring the Morphology and the Spatial Acid Site Distribution of ZSM-5 Catalysts

Chemical and Biomolecular Engineering, Department o

Elucidating the Effects of Polyprotic Acid Speciation in Calcium Oxalate Crystallization

Polyprotic acids tend to be very effective modifiers of crystals in synthetic, natural, and biological systems. Examples include calcium biomineralization where proteins and organic acids decorated with carboxylic acids act as inhibitors of crystal growth. For crystals implicated in pathological diseases, large variations in the pH of the growth medium can alter the speciation of polyprotic acids. This is particularly true for calcium minerals comprised of polyprotic counterions wherein changes in solute speciation affect supersaturation, and thus the kinetics of crystal growth. Here, we explore the combined effects of solute and modifier speciation, selecting calcium oxalate monohydrate (COM) as a representative system for calcification. COM is a major constituent of human kidney stones where crystallization <i>in vivo</i> occurs over a broad range of pH spanning 5–8. Common modifiers of COM and its solute (oxalate) are polyprotic acids. Few studies report the effects of oxalate speciation on COM growth. Moreover, it remains to be determined how pH influences the efficacy of polyprotic molecules used to inhibit COM growth, such as citrate (CA) and its molecular analogue hydroxycitrate (HCA). Here, we show that there is a dramatic reduction in the rate of COM growth in the lower limit of physiological pH, commensurate with the loss of oxalate net negative charge. Our findings reveal that CA and HCA exhibit dual modes of action as promoters and inhibitors of COM crystallization at low and high pH, respectively. We also observe distinct differences in the efficacy of each modifier and discuss how local changes in pH near charged crystal interfaces can have a marked impact on local supersaturation and the speciation of adsorbed modifiers. On the basis of our observations of COM crystallization, it is reasonable to expect that changes in pH, or more specifically the speciation of solute and modifier(s), could similarly impact the growth (and growth inhibition) of other crystals employing polyprotic acids