Special Issue "Effects of Confinement and Topography on Crystallization"

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

Deadline for manuscript submissions: closed (30 June 2017)

Special Issue Editor

Guest Editor
Dr. Hugo K. Christenson

School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, U. K
Website | E-Mail
Interests: crystal growth; nucleation; wetting; adsorption; surface forces; bubble interactions; cavitation

Special Issue Information

Dear Colleagues,

Classical nucleation theory predicts that nucleation on a surface is always favoured in comparison to homogeneous nucleation, which is in agreement with empirical observations that crystals typically grow on container walls and/or on particulate impurities. The probability of nucleation is further enhanced in surface imperfections such as grooves or pits, for which there is also strong experimental evidence and support from simulation studies. In more highly confined systems, such as porous media, not only nucleation may be affected, but also the growth and phase transformation of crystals, which depend on material transport in the medium.

This is a multidisciplinary topic with applications across the sciences, from fundamental chemistry and physics to the pharmaceutical industry, medical implants, atmospheric ice nucleation, the fabrication of optoelectronic devices and the conservation of porous building materials. Among the fundamental challenges are to better understand the large variability of topographical effects with different surfaces, and how to separate the influence of topography from that of surface chemistry. Regarding crystallisation in confinement, some key issues are differentiating between the effects of the confinement on nucleation, and how it influences the subsequent crystal growth. From an applied perspective, the ultimate goal is how to use the new knowledge to achieve better control of crystallisation.

We invite contributions on all aspects of nucleation and crystallisation in confined systems and where topography is an important factor, including crystals forming from vapour, from the melt (liquids) and from solution, in fundamental or applied disciplines.

Dr. Hugo K. Christenson
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

•    active sites
•    confinement
•    crystallization
•    nucleation
•    topography

Published Papers (3 papers)

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Research

Open AccessArticle Precipitant-Free Crystallization of Protein Molecules Induced by Incision on Substrate
Crystals 2017, 7(8), 245; doi:10.3390/cryst7080245
Received: 20 July 2017 / Revised: 1 August 2017 / Accepted: 1 August 2017 / Published: 5 August 2017
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Abstract
Nucleation of protein crystals has been shown to be facilitated by substrates decorated with both nano- to micro-scale hierarchical undulations and spatially varying surface potential. In fact, on such surfaces, several proteins were found to crystallize without having to use any precipitant in
[...] Read more.
Nucleation of protein crystals has been shown to be facilitated by substrates decorated with both nano- to micro-scale hierarchical undulations and spatially varying surface potential. In fact, on such surfaces, several proteins were found to crystallize without having to use any precipitant in contrast to all other homogeneous and heterogeneous systems in which precipitant is an essential ingredient for nucleation. While these surfaces were so patterned whole through the area that was brought in contact with the protein solution, it was not clear exactly to what extent the surfaces were required to be patterned to trigger nucleation without use of any precipitant. Here we show that a simple incision may be enough on an otherwise smooth surface for this purpose. In particular, the substrate used here is a smooth silicone film with its surface plasma oxidized to create a thin crust of silica. An incision is then generated on this surface using a sharp razor blade. The silica crust being brittle leads to random nano-microscopic undulations at the vicinity of the incision. These undulations along with surface charge can induce protein crystal nucleation without precipitant. Full article
(This article belongs to the Special Issue Effects of Confinement and Topography on Crystallization)
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Open AccessArticle Two-Stage Crystallizer Design for High Loading of Poorly Water-Soluble Pharmaceuticals in Porous Silica Matrices
Crystals 2017, 7(5), 131; doi:10.3390/cryst7050131
Received: 30 March 2017 / Revised: 2 May 2017 / Accepted: 5 May 2017 / Published: 9 May 2017
Cited by 1 | PDF Full-text (2543 KB) | HTML Full-text | XML Full-text
Abstract
While porous silica supports have been previously studied as carriers for nanocrystalline forms of poorly water-soluble active pharmaceutical ingredients (APIs), increasing the loading of API in these matrices is of great importance if these carriers are to be used in drug formulations. A
[...] Read more.
While porous silica supports have been previously studied as carriers for nanocrystalline forms of poorly water-soluble active pharmaceutical ingredients (APIs), increasing the loading of API in these matrices is of great importance if these carriers are to be used in drug formulations. A dual-stage mixed-suspension, mixed-product removal (MSMPR) crystallizer was designed in which the poorly soluble API fenofibrate was loaded into the porous matrices of pore sizes 35 nm–300 nm in the first stage, and then fed to a second stage in which the crystals were further grown in the pores. This resulted in high loadings of over 50 wt % while still producing nanocrystals confined to the pores without the formation of bulk-sized crystals on the surface of the porous silica. The principle was extended to another highly insoluble API, griseofulvin, to improve its loading in porous silica in a benchtop procedure. This work demonstrates a multi-step crystallization principle API in porous silica matrices with loadings high enough to produce final dosage forms of these poorly water-soluble APIs. Full article
(This article belongs to the Special Issue Effects of Confinement and Topography on Crystallization)
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Open AccessArticle Molecular Dynamics Simulations of Hydroxyapatite Nanopores in Contact with Electrolyte Solutions: The Effect of Nanoconfinement and Solvated Ions on the Surface Reactivity and the Structural, Dynamical, and Vibrational Properties of Water
Crystals 2017, 7(2), 57; doi:10.3390/cryst7020057
Received: 23 October 2016 / Revised: 23 January 2017 / Accepted: 10 February 2017 / Published: 18 February 2017
Cited by 1 | PDF Full-text (5912 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Hydroxyapatite, the main mineral phase of mammalian tooth enamel and bone, grows within nanoconfined environments and in contact with aqueous solutions that are rich in ions. Hydroxyapatite nanopores of different pore sizes (20 Å ≤ H ≤ 110 Å, where H is the
[...] Read more.
Hydroxyapatite, the main mineral phase of mammalian tooth enamel and bone, grows within nanoconfined environments and in contact with aqueous solutions that are rich in ions. Hydroxyapatite nanopores of different pore sizes (20 Å ≤ H ≤ 110 Å, where H is the size of the nanopore) in contact with liquid water and aqueous electrolyte solutions (CaCl2 (aq) and CaF2 (aq)) were investigated using molecular dynamics simulations to quantify the effect of nanoconfinement and solvated ions on the surface reactivity and the structural and dynamical properties of water. The combined effect of solution composition and nanoconfinement significantly slows the self-diffusion coefficient of water molecules compared with bulk liquid. Analysis of the pair and angular distribution functions, distribution of hydrogen bonds, velocity autocorrelation functions, and power spectra of water shows that solution composition and nanoconfinement in particular enhance the rigidity of the water hydrogen bonding network. Calculation of the water exchange events in the coordination of calcium ions reveals that the dynamics of water molecules at the HAP–solution interface decreases substantially with the degree of confinement. Ions in solution also reduce the water dynamics at the surface calcium sites. Together, these changes in the properties of water impart an overall rigidifying effect on the solvent network and reduce the reactivity at the hydroxyapatite-solution interface. Since the process of surface-cation-dehydration governs the kinetics of the reactions occurring at mineral surfaces, such as adsorption and crystal growth, this work shows how nanoconfinement and solvation environment influence the molecular-level events surrounding the crystallization of hydroxyapatite. Full article
(This article belongs to the Special Issue Effects of Confinement and Topography on Crystallization)
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