Themed collection Editor’s Collection: Polymorphism in Molecular Crystals
Polymorphism in p-aminobenzoic acid
We review the polymorphism of p-aminobenzoic acid (pABA), a model drug compound whose crystallisation and polymorphic behaviour has been extensively studied in recent years.
Thermosalient effect of two polymorphs of a diketopyrrolopyrrole dye with different crystal systems and molecular arrangements
Two polymorphs of a diketopyrrolopyrrole dye, one yellow and the other orange, were obtained.
SURMOF induced polymorphism and crystal morphological engineering of acetaminophen polymorphs: advantage of heterogeneous nucleation
Surface metal organic framework substrates were engineered as heterogeneous surfaces and the importance of these designed surfaces towards polymorphs and morphological engineering was discussed for the first time.
Unusual seeding effect in the liquid-assisted high-pressure polymorphism of chlorpropamide
When crystals of four polymorphs – a stable α-form and three metastable ones (β-, γ-, δ-forms) – are simultaneously present in a pressure cell, immersed in a 1 : 1 pentane–isopentane mixture, the least stable β-form recrystallises exclusively into the γ-form (if no δ-form seed is present) or concomitantly into the γ- and δ-forms (if a seed of the δ-form is present).
An unprecedented case of dodecamorphism: the twelfth polymorph of aripiprazole formed by seeding with its active metabolite
Twelfth polymorph of the anti-psychotic drug aripiprazole was discovered where its active metabolite acted as a template during recrystallization.
Ostwald's rule and enantiotropy: polymorph appearance in the crystallisation of p-aminobenzoic acid
The development of rational crystallisation strategies in polymorphic systems requires the experimental manipulation of both kinetics and thermodynamics.
High-pressure polymorphism in L-threonine between ambient pressure and 22 GPa
The amino acid L-threonine undergoes three phase transitions between ambient pressure and 22.3 GPa which modify both hydrogen bonding and the molecular conformation.
Crystallisation in printed droplets: understanding crystallisation of D-mannitol polymorphs
Crystallising D-mannitol in printed droplets provides new insights into understanding the effect of foreign surfaces on the formation of its polymorphs.
On the prevalence of smooth polymorphs at the nanoscale: implications for pharmaceuticals
Ball mill neat grinding leads to smoother whereas liquid assisted grinding leads to rougher pharmaceutical forms.
Polymorph control in batch seeded crystallizers. A case study with paracetamol
We show that seeding is not always sufficient to control cystal polymorphism and illustrate how kinetic modeling can help controlling polymorphism.
Robust bulk preparation and characterization of sulfamethazine and saccharine salt and cocrystal polymorphs
The complex between sulfamethazine and saccharine (SMT–SAC) can exist in two polymorphs, one is a cocrystal and the other is a salt.
A new polymorph of the common coformer isonicotinamide
A polymorph of the widely employed coformer isonicotinamide crystallizing in the space group Pca21 is described for the first time.
Solid state photodimerization of 9-tert-butyl anthracene ester produces an exceptionally metastable polymorph according to first-principles calculations
Molecular crystal engineering seeks to tune the material properties by controlling the crystal packing.
Exploring polymorphism and stoichiometric diversity in naproxen/proline cocrystals
This work studies a multitude of cocrystals obtained by combining chiral and/or racemic naproxen and proline, 17 in total.
Serendipitous isolation of a disappearing conformational polymorph of succinic acid challenges computational polymorph prediction
A new polymorph of succinic acid is an unusually challenging test for metastable polymorph prediction.
Polymorphism of chlorpropamide on liquid-assisted mechanical treatment: choice of liquid and type of mechanical treatment matter
Different types of mechanical treatment (tableting, grinding, milling, etc.) are important technological operations in the pharmaceutical industry.
L-Malic acid crystallization: polymorphism, semi-spherulites, twisting, and polarity
A new polymorph and twisted semi-spherulites of L-malic acid are described and discussed in this work.
Polymorphism in secondary squaramides: on the importance of π-interactions involving the four membered ring
We report the crystal structures of four new squaric acid derivatives, i.e. three polymorphs of 3,4-bis((2-(dimethylamino)ethyl)amino)cyclobut-3-ene-1,2-dione (1a–c) and a cocrystal with resorcinol. A DFT study has been also carried out to investigate the supramolecular assemblies.
Effect of pressure on two polymorphs of tolazamide: why no interconversion?
Pressure-resistant transformation between two polymorphs of tolazamide was monitored by X-ray diffraction and rationalized by DFT calculations.
Polymorphism, isostructurality and physicochemical properties of glibenclamide salts
Glibenclamide sodium salt polymorphs namely forms I and II showed differences in geometry of the central metal atom and ligand orientation. The solubility and stability of glibenclamide of GBA-K form I are superior for pharmaceutical development.
4-Aminoquinaldine monohydrate polymorphism: prediction and impurity aided discovery of a difficult to access stable form
Crystal structure prediction studies of 4-aminoquinaldine monohydrate led, 80 years after its first synthesis, to the thermodynamically most stable form under conditions relevant for production and storage.
Polymorphism of vanillin revisited: the discovery and selective crystallization of a rare crystal structure
65 years ago McCrone postulated vanillin to be trimorphic but only one polymorph has been structurally characterized since. Herein, a new and rare crystal structure is reported. Selective crystallization of this polymorph was achieved using polymer induced heterogeneous nucleation.
Static and lattice vibrational energy differences between polymorphs
Lattice energy, entropy and free energy differences for over 500 pairs of known polymorphs are computed and discussed.
Concerning the crystal morphologies of the α and β polymorphs of p-aminobenzoic acid
A detailed morphological study on an organic polymorphic system highlighting the influence of desolvation on crystal habit.
About this collection
This Editor’s collection, guest edited by Editorial Board member Aurora Cruz-Cabeza, highlights a number of recent articles in the field of Polymorphism in Molecular Crystals. Contributions include the discovery of new elusive polymorphs, the development of new strategies for polymorph control or the study of crystallisation and milling processes and their impact on polymorphism.
We dedicate this collection to the late Professor Joel Bernstein who endeavoured much of his work to the study of polymorphism and inspired many of us.