Polymorphism in Crystals

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

Deadline for manuscript submissions: closed (20 February 2023) | Viewed by 23326

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Special Issue Editors

Dr. Jingxiang Yang
E-Mail Website
Guest Editor
State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China
Interests: polymorph; pesticide; crystal engineering
National Engineering Research Center of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
Interests: polymorph; crystal engineering; functional crystal material
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Special Issue Information

Dear Colleagues,

Polymorphism, the property of a compound to crystallize in more than one distinct crystal form, plays an indispensable role in researching and developing pharmaceuticals, agrochemicals, materials, and food. Polymorphs exhibit different properties, such as crystal habit, solubility, dissolution rate, melting point, stability, mechanical properties, even bioavailability, which may influence product quality. Therefore, the study on polymorphs’ behavior can provide a theoretical basis for selecting optimal solid forms and serve for the polymorphic control and optimization of products as a primary method. Recently, significant progress has been made in the experimental discovery and theoretical prediction of crystal polymorphs. A large quantity of molecules have been discovered to have polymorphs that are mainly attributed to the molecule’s conformational flexibility and the existence of various functionalities in the molecule that could act as hydrogen bond donor/acceptor.  In addition to conventional solution crystallization, more polymorphisms have been found in the melt, in confinement, and in the presence of ultrasound/lasers.

Moreover, computational predictions usually yield far more possible polymorphs than are known. The ultimate limitations of experimental reachable polymorphs and thermodynamical and structure–activity relationships of the polymorphs remain an open question. The present Special Issue on “Polymorphism in Crystals” invites status reports summarizing the progress achieved in recent years.

Dr. Jingxiang Yang
Prof. Dr. Xin Huang
Guest Editors

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Published Papers (13 papers)

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13 pages, 15914 KiB  
Article
The Influence of Different Types of SiO2 Precursors and Ag Addition on the Structure of Selected Titania-Silica Gels
Crystals 2023, 13(5), 811; https://doi.org/10.3390/cryst13050811 - 13 May 2023
Cited by 2 | Viewed by 833
Abstract
In this paper, samples of titania-silica system were obtained by the sol-gel method as bulk materials, using titanium propoxide Ti(C3H7O)4 to introduce titania and two precursors of SiO2: TEOS tetraethoxysilane Si(OC2H5)4 [...] Read more.
In this paper, samples of titania-silica system were obtained by the sol-gel method as bulk materials, using titanium propoxide Ti(C3H7O)4 to introduce titania and two precursors of SiO2: TEOS tetraethoxysilane Si(OC2H5)4 and DDS dimethyldiethoxysilane (CH3)2(C2H5O)2Si. To enhance antibacterial properties, Ag was added to gels of selected compositions. The main aim of the performed studies was to find the correlations between the structural changes and the applied precursor of silica. Simultaneously, the influence of different compositions of gels and the addition of Ag on the specimens’ structure was investigated. To study the structure, two complementary methods, FTIR (Fourier Transform InfraRed) spectroscopy and X-ray diffraction, were applied. The analysis of the FTIR spectra and the XRD patterns made it possible to confirm the amorphous state of all dried gels and establish the presence of TiO2 polymorphs: anatase and rutile in all annealed samples. The addition of Ag atoms into the gels caused the crystallization of cristobalite phase in addition to titania polymorphs. The presence of crystalline Ag phase in the annealed gels allowed the calculation dimensions of Ag crystallites based on the Scherrer equation. The use of DDS as a silica precursor led to easier and faster crystallization of different TiO2 phases in the annealed samples and parallel increases in the depolymerization of silica lattice. Full article
(This article belongs to the Special Issue Polymorphism in Crystals)
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