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Crystals
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Nonclassical Nucleation—Role of Metastable Intermediate Phase on Crystal Nucleation
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Nonclassical Nucleation—Role of Metastable Intermediate Phase on Crystal Nucleation

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 16478

Special Issue Editors

Dr. Fajun Zhang

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Guest Editor
Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
Interests: small angle scattering; protein crystallization; phase behavior in protein solution; liquid-liquid phase separation
Dr. José Gavira

E-Mail Website
Guest Editor
IACT (CSIC-UGR), Armilla, Spain
Interests: protein crystallization: nucleation, growth and crystals quality; protein crystallography; protein crystals biocompostites and properties; enzymatic crystals (CLEC)
Special Issues, Collections and Topics in MDPI journals
Dr. Geun Woo Lee

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Guest Editor
Korea Research Institute of Standards and Science, Daejeon, Korea
Interests: nucleation; liquid structure; thermophysical properties of liquid metals and alloys; glass formation; crystallization
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Dirk Zahn

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Guest Editor
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) Nägelsbachstrasse 25, 91052 Erlangen, Germany
Interests: theoretical chemistry; atomistic simulation with focus on nucleation processes and material chemistry

Special Issue Information

Dear Colleagues,

Classical nucleation theory (CNT), which was established about 90 years ago, has been very successful in many research fields, and continues to be the most commonly used theory in describing the nucleation process. For a fluid-to-solid phase transition, CNT states that the solute molecules in a supersaturated solution reversibly form small clusters. Once the cluster size reaches a critical value, it becomes thermodynamically stable and is favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously.

Recent studies in experiments, computer simulations and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists between the initial supersaturated solution and the final crystals. Depending on the exact free energy landscapes, the MIPs can be a high-density liquid phase, mesoscopic clusters, or a pre-ordered state.

In this Topic, we focus on the role of the various MIPs on the early stage of crystal nucleation. Such MIPs have been observed in organic materials, minerals, colloids and proteins, resulting in various scenarios of nonclassical pathways of crystallization. Efforts are required on the characterization of the structural and dynamical properties of MIPs, the growth kinetics of both MIPs and crystals, as well as the theoretical understanding of the decoupling of order parameters.

Dr. Fajun Zhang
Dr. José Gavira
Dr. Geun Woo Lee
Prof. Dr. Dirk Zahn
Guest Editors

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Keywords

  • Nonclassical nucleation
  • Two-step nucleation
  • Metastable intermediate phase
  • Liquid-liquid phase transition
  • Mesoscopic clusters
  • Decoupling of order parameter
  • Real-time small angle scattering
  • Cryo-TEM

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Published Papers (5 papers)

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22 pages, 7995 KiB  
Article
Exploring Nucleation Pathways in Distinct Physicochemical Environments Unveiling Novel Options to Modulate and Optimize Protein Crystallization
by Mengying Wang, Angélica Luana C. Barra, Hévila Brognaro and Christian Betzel
Crystals 2022, 12(3), 437; https://doi.org/10.3390/cryst12030437 - 21 Mar 2022
Cited by 3 | Viewed by 3179
Abstract
The scientific discussion about classical and nonclassical nucleation theories has lasted for two decades so far. Recently, multiple nucleation pathways and the occurrence and role of metastable intermediates in crystallization processes have attracted increasing attention, following the discovery of functional phase separation, which [...] Read more.
The scientific discussion about classical and nonclassical nucleation theories has lasted for two decades so far. Recently, multiple nucleation pathways and the occurrence and role of metastable intermediates in crystallization processes have attracted increasing attention, following the discovery of functional phase separation, which is now under investigation in different fields of cellular life sciences, providing interesting and novel aspects for conventional crystallization experiments. In this context, more systematic investigations need to be carried out to extend the current knowledge about nucleation processes. In terms of the data we present, a well-studied model protein, glucose isomerase (GI), was employed first to investigate systematically the early stages of the crystallization process, covering condensing and prenucleation ordering of protein molecules in diverse scenarios, including varying ionic and crowding agent conditions, as well as the application of a pulsed electric field (pEF). The main method used to characterize the early events of nucleation was synchronized polarized and depolarized dynamic light scattering (DLS/DDLS), which is capable of collecting the polarized and depolarized component of scattered light from a sample suspension in parallel, thus monitoring the time-resolved evolution of the condensation and geometrical ordering of proteins at the early stages of nucleation. A diffusion interaction parameter, KD, of GI under varying salt conditions was evaluated to discuss how the proportion of specific and non-specific protein–protein interactions affects the nucleation process. The effect of mesoscopic ordered clusters (MOCs) on protein crystallization was explored further by adding different ratios of MOCs induced by a pEF to fresh GI droplets in solution with different PEG concentrations. To emphasize and complement the data and results obtained with GI, a recombinant pyridoxal 5-phosphate (vitamin B6) synthase (Pdx) complex of Staphylococcus aureus assembled from twelve monomers of Pdx1 and twelve monomers of Pdx2 was employed to validate the ability of the pEF influencing the nucleation of complex macromolecules and the effect of MOCs on adjusting the crystallization pathway. In summary, our data revealed multiple nucleation pathways by tuning the proportion of specific and non-specific protein interactions, or by utilizing a pEF which turned out to be efficient to accelerate the nucleation process. Finally, a novel and reproducible experimental strategy, which can adjust and facilitate a crystallization process by pEF-induced MOCs, was summarized and reported for the first time. Full article
(This article belongs to the Special Issue Nonclassical Nucleation—Role of Metastable Intermediate Phase on Crystal Nucleation)
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16 pages, 3690 KiB  
Article
The Ambiguous Functions of the Precursors That Enable Nonclassical Modes of Olanzapine Nucleation and Growth
by Monika Warzecha, Alastair J. Florence and Peter G. Vekilov
Crystals 2021, 11(7), 738; https://doi.org/10.3390/cryst11070738 - 26 Jun 2021
Cited by 6 | Viewed by 2499
Abstract
One of the most consequential assumptions of the classical theories of crystal nucleation and growth is the Szilard postulate, which states that molecules from a supersaturated phase join a nucleus or a growing crystal individually. In the last 20 years, observations in complex [...] Read more.
One of the most consequential assumptions of the classical theories of crystal nucleation and growth is the Szilard postulate, which states that molecules from a supersaturated phase join a nucleus or a growing crystal individually. In the last 20 years, observations in complex biological, geological, and engineered environments have brought to light violations of the Szilard rule, whereby molecules assemble into ordered or disordered precursors that then host and promote nucleation or contribute to fast crystal growth. Nonclassical crystallization has risen to a default mode presumed to operate in the majority of the inspected crystallizing systems. In some cases, the existence of precursors in the growth media is admitted as proof for their role in nucleation and growth. With the example of olanzapine, a marketed drug for schizophrenia and bipolar disorder, we demonstrate that molecular assemblies in the solution selectively participate in crystal nucleation and growth. In aqueous and organic solutions, olanzapine assembles into both mesoscopic solute-rich clusters and dimers. The clusters facilitate nucleation of crystals and crystal form transformations. During growth, however, the clusters land on the crystal surface and transform into defects, but do not support step growth. The dimers are present at low concentrations in the supersaturated solution, yet the crystals grow by the association of dimers, and not of the majority monomers. The observations with olanzapine emphasize that detailed studies of the crystal and solution structures and the dynamics of molecular association may empower classical and nonclassical models that advance the understanding of natural crystallization, and support the design and manufacture of promising functional materials. Full article
(This article belongs to the Special Issue Nonclassical Nucleation—Role of Metastable Intermediate Phase on Crystal Nucleation)
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10 pages, 1619 KiB  
Article
Retained Free Energy with Enhanced Nucleation during Electrostatic Levitation of Undercooled Fe-Co Alloys
by Douglas M. Matson, Xuanjiang Liu, Justin E. Rodriguez, Sangho Jeon and Olga Shuleshova
Crystals 2021, 11(7), 730; https://doi.org/10.3390/cryst11070730 - 24 Jun 2021
Cited by 2 | Viewed by 1823
Abstract
Double recalescence in many ferrous alloy systems involves rapid solidification of metastable ferrite from the undercooled melt with subsequent transformation to stable austenite. Containerless processing is used to monitor the process using pyrometry and high-speed cinematography such that delay behavior can be predicted [...] Read more.
Double recalescence in many ferrous alloy systems involves rapid solidification of metastable ferrite from the undercooled melt with subsequent transformation to stable austenite. Containerless processing is used to monitor the process using pyrometry and high-speed cinematography such that delay behavior can be predicted based on the application of the retained damage model (RDM). When comparing Fe-Cr-Ni alloys to Fe-Co alloys, the cluster attachment rate is enhanced while free energy retention is reduced. These trends are tied to specific alloy properties. A retained free energy criterion is proposed based on the ratio of thermophysical properties used to define the transformation driving force such that the thermodynamic limit for energy retention may be predicted. Surprisingly, at long delay times, healing occurs such that much of the retained free energy is not available to enhance the transition from metastable to stable phases. At delay times less than one second, no healing is observed and the RDM correctly predicts transformation delay behavior over a wide range of alloy compositions. Full article
(This article belongs to the Special Issue Nonclassical Nucleation—Role of Metastable Intermediate Phase on Crystal Nucleation)
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12 pages, 1968 KiB  
Article
Tuning Transport Phenomena in Agarose Gels for the Control of Protein Nucleation Density and Crystal Form
by Fiora Artusio, Albert Castellví, Roberto Pisano and José A. Gavira
Crystals 2021, 11(5), 466; https://doi.org/10.3390/cryst11050466 - 22 Apr 2021
Cited by 7 | Viewed by 3303
Abstract
Agarose gels provide the ideal environment for studying the nucleation step of complex biomacromolecules under diffusion-controlled conditions. In the present paper, we characterized the influence of agarose on the nucleation of three model proteins, i.e., lysozyme, insulin, and proteinase K, as a function [...] Read more.
Agarose gels provide the ideal environment for studying the nucleation step of complex biomacromolecules under diffusion-controlled conditions. In the present paper, we characterized the influence of agarose on the nucleation of three model proteins, i.e., lysozyme, insulin, and proteinase K, as a function of the agarose concentration using a batch method set-up inside flat capillaries. By using this set-up, we were able to directly count the number of crystals in a given volume and correlate it with the amount of agarose and with the average crystal size. We also studied the crystallization behavior of proteinase K with free-interface diffusion so that batch conditions were achieved through slow diffusion of the precipitant. Thanks to the control over the protein mass transport imposed by the network, a previously unknown crystal form, P212121, was obtained, and the three-dimensional structure was determined at a 1.6 Å resolution. Overall, the versatility of agarose gels makes them ideal candidates for the preparation of microcrystalline suspensions of biopharmaceuticals with precise and reproducible crystal attributes or for the exploration of the existence of different polymorphs. Full article
(This article belongs to the Special Issue Nonclassical Nucleation—Role of Metastable Intermediate Phase on Crystal Nucleation)
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8 pages, 381 KiB  
Perspective
Nonclassical Nucleation—Role of Metastable Intermediate Phase in Crystal Nucleation: An Editorial Prefix
by Fajun Zhang, José A. Gavira, Geun Woo Lee and Dirk Zahn
Crystals 2021, 11(2), 174; https://doi.org/10.3390/cryst11020174 - 10 Feb 2021
Cited by 9 | Viewed by 4331
Abstract
Classical nucleation theory (CNT), which was established about 90 years ago, represents the most commonly used theory in describing nucleation processes. For a fluid-to-solid phase transition, CNT states that the solutes in a supersaturated solution reversibly form small clusters. Once a cluster reaches [...] Read more.
Classical nucleation theory (CNT), which was established about 90 years ago, represents the most commonly used theory in describing nucleation processes. For a fluid-to-solid phase transition, CNT states that the solutes in a supersaturated solution reversibly form small clusters. Once a cluster reaches its critical size, it becomes thermodynamically stable and is favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations, and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists in parallel to the initial supersaturated solution and the final crystals. These MIPs can be high-density liquid phases, mesoscopic clusters, or preordered states. In this Special Issue, we focus on the role of the various MIPs in the early stage of crystal nucleation of organic materials, metals and alloys, aqueous solutions, minerals, colloids, and proteins, and thus on various scenarios of nonclassical pathways of crystallization. Full article
(This article belongs to the Special Issue Nonclassical Nucleation—Role of Metastable Intermediate Phase on Crystal Nucleation)
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