Exploring the effects of high pressure on hydrogen bonding in pharmaceutical cocrystals: A systematic study of pyridine dicarboxylic acid systems using synchrotron and neutron diffraction

Pharmaceutical cocrystals use common robust hydrogen bonding synthons to create novel materials with different physicochemical properties. In this systematic study of a series of cocrystals, we explore the effect of high pressure on one of these commonly used motifs, the acid-pyridine motif, to assess the commonality of behaviour under extreme conditions. We have surveyed five pyridine dicarboxylic acid systems using both synchrotron and neutron diffraction methods to elucidate the changes in structure. We observe that the hydrogen bonding in these systems compress at a similar rate despite the changes to the molecular make-up of the solids and that on compression the changes in structure are indicative that the layers move along the major slip planes in the structure. We have observed two phase transitions to new forms of the pyrazine:malonic acid system, one for each stoichiometric ratio. This study demonstrates that the combination of two complementary diffraction approaches is key to understanding polymorphic behaviour at high pressure.

Dehydration of Niclosamide Monohydrate Polymorphs: Different Mechanistic Pathways to the Same Product

Many active pharmaceutical ingredients (APIs) can crystallize as hydrates or anhydrates, the relative stability of which depends on their internal structures as well as the external environment. Hydrates may dehydrate unexpectedly or intentionally, though the molecular-level mechanisms by which such transformations occur are difficult to predict a priori. Niclosamide is an anthelmintic drug on the World Health Organization's "List of Essential Medicines" that crystallizes in two monohydrate forms: HA and HB. Through complementary time-resolved synchrotron powder X-ray diffraction and thermogravimetric kinetic studies, we demonstrate that the two monohydrates dehydrate via distinctly different solid state pathways yet yield the same final anhydrate phase. Water loss from HA via diffusion yields an isomorphous desolvate intermediate which can rearrange to at least two different polymorphs, only one of which exhibits long-term stability. In contrast, dehydration of HB proceeds via a surface nucleation process where simultaneous water loss and product formation occur with no detectable crystalline intermediates. Comparative analysis of the two systems serves to highlight the complex relationship between lattice structure and solid state dehydration processes.

Virtual Screening, Structural Analysis, and Formation Thermodynamics of Carbamazepine Cocrystals

In this study, the existing set of carbamazepine (CBZ) cocrystals was extended through the successful combination of the drug with the positional isomers of acetamidobenzoic acid. The structural and energetic features of the CBZ cocrystals with 3- and 4-acetamidobenzoic acids were elucidated via single-crystal X-ray diffraction followed by QTAIMC analysis. The ability of three fundamentally different virtual screening methods to predict the correct cocrystallization outcome for CBZ was assessed based on the new experimental results obtained in this study and data available in the literature. It was found that the hydrogen bond propensity model performed the worst in distinguishing positive and negative results of CBZ cocrystallization experiments with 87 coformers, attaining an accuracy value lower than random guessing. The method that utilizes molecular electrostatic potential maps and the machine learning approach named CCGNet exhibited comparable results in terms of prediction metrics, albeit the latter resulted in superior specificity and overall accuracy while requiring no time-consuming DFT computations. In addition, formation thermodynamic parameters for the newly obtained CBZ cocrystals with 3- and 4-acetamidobenzoic acids were evaluated using temperature dependences of the cocrystallization Gibbs energy. The cocrystallization reactions between CBZ and the selected coformers were found to be enthalpy-driven, with entropy terms being statistically different from zero. The observed difference in dissolution behavior of the cocrystals in aqueous media was thought to be caused by variations in their thermodynamic stability.

Complex Growth of Benzamide Form I: Effect of Additives, Solution Flow, and Surface Rugosity

Understanding crystal growth kinetics is of great importance for the development and manufacturing of crystalline molecular materials. In this work, the impact of additives on the growth kinetics of benzamide form I (BZM-I) crystals has been studied. Using our newly developed crystal growth setup for the measurement of facet-specific crystal growth rates under flow, BZM-I growth rates were measured in the presence of various additives previously reported to induce morphological changes. The additives did not have a significant impact on the growth rates of BZM-I at low concentrations. By comparison to other systems, these additives could not be described as "effective" since BZM-I showed a high tolerance of the additives' presence during growth, which may be a consequence of the type of growth mechanisms at play. Growth of pure BZM-I was found to be extremely defected, and perhaps those defects allow the accommodation of impurities. An alternative explanation is that at low additive concentrations, solid solutions are formed, which was indeed confirmed for a few of the additives. Additionally, the growth of BZM-I was found to be significantly affected by solution dynamics. Changes in some facet growth rates were observed with changes in the orientation of the BZM-I single crystals relative to the solution flow. Of the two sets of facets involved in the growth of the width and length of the crystal, the {10l̅} facets were found to be greatly affected by the solution flow while the {011} facets were not affected at all. Computational fluid dynamics simulations showed that solute concentration has higher gradients at the edges of the leading edge {10l̅} facets, which can explain the appearance of satellite crystals. {10l̅} facets were found to show significant structural rugosity at the molecular level, which may play a role in their mechanism of growth. The work highlights the complexities of measuring crystal growth data of even simple systems such as BZM-I, specifically addressing the effect of additives and fluid dynamics.

Pervasive approximate periodic symmetry in organic P1 structures

The goal of this project was to identify the prevalence of approximate symmetry in organic P1 structures. In the November 2019 version of the Cambridge Structural Database (CSD), there are 2592 organic, P1, R ≤ 0.050 structures; complete, unique entries are available for 1407 Z = Z' > 1 and 1049 Z = Z' = 1 structures. All the Z > 1 structures can have approximate symmetry; the Z = 1 structures were scanned to find those composed of molecules or ions that might lie on a special position and those that have two or more large molecules or ions that are very similar. The number of Z = 1 structures so identified was 285, of which 49 were grouped with the Z > 1 structures because Z_effective > 1. The packing in each of the 1407 + 285 = 1692 structures was investigated. The 144 that should almost certainly have been described in a smaller or higher-symmetry unit cell were removed from the list; 120 of the 144 are composed of achiral or racemic material. (About half of the Z = 1 and 89% of the Z > 1 structures are composed of enantiopure material.) Approximate periodic symmetry was found in 86% of the 1337 remaining Z > 1 structures and in 72% of the 211 remaining Z = 1 structures. About a third of the enantiomerically pure structures mimic inversion symmetry; 38% have approximate rotational symmetry. For the structures of achiral and racemic material, distorted glide or mirror symmetry is more common than is distorted inversion symmetry. Approximate rotational and glide symmetry was found to be periodic in two dimensions considerably more often than in three. In 4% of the structures, different layer types alternate or layers are related by approximate local rotations, as well as by small translations. In 5% of the structures, different parts of the molecule are segregated into two-dimensional regions that have different approximate symmetries. More than a third of the structures that are a distorted version of a higher-symmetry structure were determined at T ≥ 288 K.

An extended macroindentation method for determining the hardness of poorly compressible materials

Indentation hardness, H, is an important mechanical property that quantifies the resistance to deformation by a material. For pharmaceutical powders, H can be determined using a macroindentation method, provided they can form intact tablets suitable for testing. This work demonstrates a method for determining the hardness of problematic materials that cannot form suitable tablets for macroindentation. The method entails predicting the hardness of a given powder at zero porosity (H₀) from those of microcrystalline cellulose and its binary mixture with the test compound using a power law mixing rule based on weight fraction. This method was found suitable for 13 binary mixtures. In addition, the H₀ values derived by this method could capture changes due to different particle sizes of sucrose and sodium chloride. Furthermore, the derived H₀ reasonably agreed with the single crystal indentation hardness of a set of 16 crystals when accounting for the effect of indentation condition and structural anisotropy. The mixture method thus extends the use of macroindentation for predicting indentation hardness of powders that cannot form intact tablets and, hence, their plasticity.

Evaluating structure-property relationship in a new family of mechanically flexible co-crystals

A structure-property analysis of ten compositionally and chemically similar co-crystals of N-(pyridin-2-yl)alkylamides and carboxylic acids show that three co-crystals of targets bearing a methyl chain were brittle, while the remaining...

Mechanical twinning in organic crystals

Various kinds of organic crystals can deform beyond their elastic limit, show unique mechanical properties, and switch directions of anisotropic functions by mechanical twinning based on stress-induced molecular movements.

Flexible organic crystals. Understanding the tractable co-existence of elastic and plastic bending

As an emerging class of flexible materials, mechanically bendable molecular crystals are broadly classified as elastic or plastic. Nevertheless, flexible organic crystals with mutually exclusive elastic and plastic traits, with contrasting structural requirements, co-existing under different stress settings are exceptional; hence, it is imperative to establish the concurring factors that beget this rare occurrence. We report a series of halogen-substituted benzil crystals showing elastic bending (within ∼2.45% strain), followed by elastoplastic deformation under ambient conditions. Under higher stress settings, they display exceptional plastic flexibility that one could bend, twist, or even coil around a capillary tube. X-ray diffraction, microscopy, and computational data reveal the microscopic and macroscopic basis for the exciting co-existence of elastic, elastoplastic, and plastic properties in the crystals. The layered molecular arrangement and the weak dispersive interactions sustaining the interlayer region provide considerable tolerance towards breaking and making upon engaging or releasing the external stress; it enables restoring the original state within the elastic strain. Comparative studies with oxalate compounds, wherein the twisted diketo moiety in benzil was replaced with a rigid and coplanar central oxalate moiety, enabled us to understand the effect of the anisotropy factor on the crystal packing induced by the C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O⋯C tetral interactions. The enhanced anisotropy depreciated the elastic domain, making the oxalate crystals more prone to plastic deformation. Three-point bending experiments and the determined Young's moduli further corroborate the co-existence of the elastic and plastic realm and highlight the critical role of the underlying structural elements that determine the elastic to plastic transformation. The work highlights the possible co-existence of orthogonal mechanical characteristics in molecular crystals and further construed the concurrent role of microscopic and macroscopic elements in attaining this exceptional mechanical trait.

Structural and mechanical studies of benzil and oxalate crystals highlight the microscopic and macroscopic basis for the co-existence of orthogonal mechanical traits and the elastic to plastic transformation under different stress settings.

Temperature-Reliant Dynamic Properties and Elasto-Plastic to Plastic Crystal (Rotator) Phase Transition in a Metal Oxyacid Salt

Although, dynamic crystals are attractive for use in many technologies, molecular level mechanisms of various solid-state dynamic processes and their interdependence, remain poorly understood. Here, we report a rare example of a dynamic crystal (1), involving a heavy transition metal, rhenium, with an initial two-face elasticity (within ≈1 % strain), followed by elasto-plastic deformation, at room temperature. Further, these crystals transform to a rotator (plastic) crystal phase at ≈105 °C, displaying exceptional malleability. Qualitative and quantitative mechanical tests, X-ray diffraction, μ-Raman and polarized light microscopy experiments reveal that the elasto-plastic deformation involves both partial molecular rotations and slip, while malleability in the rotator phase is facilitated by reorientational motions and increased symmetry (slip planes). Our work, connecting the plastically bendable (1D or 2D) crystals with the rotator phases (3D), is important for designing multi-functional dynamic crystals.

Progress in Research on Artificial Intelligence Applied to Polymorphism and Cocrystal Prediction

Artificial intelligence (AI) is a technology that builds an artificial system with certain intelligence and uses computer software and hardware to simulate intelligent human behavior. When combined with drug research and development, AI can considerably shorten this cycle, improve research efficiency, and minimize costs. The use of machine learning to discover novel materials and predict material properties has become a new research direction. On the basis of the current status of worldwide research on the combination of AI and crystal form and cocrystal, this mini-review analyzes and explores the application of AI in polymorphism prediction, crystal structure analysis, crystal property prediction, cocrystal former (CCF) screening, cocrystal composition prediction, and cocrystal formation prediction. This study provides insights into the future applications of AI in related fields.

Modulation of the powder properties of lamotrigine by crystal forms

The mechanical properties of powders determine the ease of manufacture and ultimately the quality of the oral solid dosage forms. Although poor mechanical properties of an active pharmaceutical ingredient (API) can be mitigated by using suitable excipients in a formulation, the effectiveness of that approach is limited for high dose drugs or multidrug tablets. In this context, improving the mechanical properties of the APIs through solid form optimisation is a good strategy to address such a challenge. This work explores the powder and tableting properties of various lamotrigine (LAM) solid forms with the aim to facilitate direct compression by overcoming the poor tabletability of LAM. The two drug-drug crystals of LAM with nicotinamide and valproic acid demonstrate superior flowability and tabletability over LAM. The improved powder properties are rationalised by structure analysis using energy framework, scanning electron microscopy, and Heckel analysis.

The unexpected discovery of the ninth polymorph of tolfenamic acid

A new polymorph of tolfenamic acid, form IX, has been crystallised from a simple cooling crystallisation experiment raising the question as to why this polymorph had never been reported before.

Potential and challenges of engineering mechanically flexible molecular crystals

Crystal adaptronics has undergone tremendous developments that have been utilized to rationalize dynamics in crystals. This highlight discusses about the role of intermolecular interactions in rationalizing mechanical responses in crystals.

Probing anisotropic mechanical behaviour in carbamazepine form III

Nanoindentation measurements in single crystals of carbamazepine form III show that the (020) face is stiffer and harder than the (002) and (101) faces. AFM imaging and molecular simulations reveal that the (020) plane is the most likely slip plane.

Impact of polymorphism on mechanical properties of molecular crystals: a study of p-amino and p-nitro benzoic acid with nanoindentation

We report on nanoindentation data for two pairs of polymorphic compounds of p-aminobenzoic acid (pABA) and p-nitrobenzoic acid (pNBA) and compare it with existing data in the literature. We also explore on a new parameter, s-PBC, as a tool to estimate hardness.

Mapping the cooperativity pathways in spin crossover complexes

Crystal packing energy calculations are applied to the [Fe(PM-L)₂(NCS)₂] family of spin crossover (SCO) complexes (PM-L = 4-substituted derivatives of the N-(2-pyridylmethylene)-4-aminobiphenyl ligand) with the aim of relating quantitatively the cooperativity of observed SCO transitions to intermolecular interactions in the crystal structures. This approach reveals a linear variation of the transition abruptness with the sum of the magnitudes of the interaction energy changes within the first molecular coordination sphere in the crystal structure. Abrupt transitions are associated with the presence of significant stabilising and destabilising changes in intermolecular interaction energies. While the numerical trend established for the PM-L family does not directly extend to other classes of SCO complex in which the intermolecular interactions may be very different, a plot of transition abruptness against the range of interaction energy changes normalised by the largest change shows a clustering of complexes with similar transition abruptness. The changes in intermolecular interactions are conveniently visualised using energy difference frameworks, which illustrate the cooperativity pathways of an SCO transition.

The abruptness of spin crossover (SCO) is related to intermolecular energy changes occurring over the course of an SCO transition. Crossover is abrupt when SCO-induced strain is accommodated synergistically in a few key interactions.

Transforming Computed Energy Landscapes into Experimental Realities: The Role of Structural Rugosity

We exploit the possible link between structural surface roughness and difficulty of crystallisation. Polymorphs with smooth surfaces may nucleate and crystallise more readily than polymorphs with rough surfaces. The concept is applied to crystal structure prediction landscapes and reveals a promising complementary way of ranking putative crystal structures.

Development of piroxicam mini-tablets enabled by spherical cocrystallization

We examined the potential of the spherical cocrystallization (SCC) technology in simultaneously enhancing tablet manufacturability and dissolution of poorly soluble drugs by developing a mini-tablet formulation of piroxicam. The manufacturing of mini-tablets using a direct compression (DC) process is more challenging than conventional tablets because of the much stricter requirement on the micromeritic properties of formulated powders. The SCC process in this work involved two steps: 1) preparing a new piroxicam-ferulic acid (PRX-FA) cocrystal, and 2) forming spherical agglomerates with the aid of a suitable bridging liquid. The PRX-FA cocrystal exhibited enhanced solubility as well as improved plasticity. The bridging liquid, a mixture of chloroform and ethyl acetate (EA) (1: 2, v/v), was chosen based on the high computed adsorption energy of chloroform and EA on morphologically dominating crystal faces of PRX-FA. The improved flowability, tabletability, and dissolution rate of spherical PRX-FA enabled the successful development of a DC mini-tablet formulation with a high PRX loading (41 wt%). This example shows that SCC is a powerful enabling technology for DC tablet formulation development of challenging drugs.

Minimizing Polymorphic Risk through Cooperative Computational and Experimental Exploration

We combine state-of-the-art computational crystal structure prediction (CSP) techniques with a wide range of experimental crystallization methods to understand and explore crystal structure in pharmaceuticals and minimize the risk of unanticipated late-appearing polymorphs. Initially, we demonstrate the power of CSP to rationalize the difficulty in obtaining polymorphs of the well-known pharmaceutical isoniazid and show that CSP provides the structure of the recently obtained, but unsolved, Form III of this drug despite there being only a single resolved form for almost 70 years. More dramatically, our blind CSP study predicts a significant risk of polymorphism for the related iproniazid. Employing a wide variety of experimental techniques, including high-pressure experiments, we experimentally obtained the first three known nonsolvated crystal forms of iproniazid, all of which were successfully predicted in the CSP procedure. We demonstrate the power of CSP methods and free energy calculations to rationalize the observed elusiveness of the third form of iproniazid, the success of high-pressure experiments in obtaining it, and the ability of our synergistic computational-experimental approach to “de-risk” solid form landscapes.

Nanoindentation of Molecular Crystals: Lessons Learned from Aspirin

Nanoindentation enables the measurement of mechanical properties from single crystals with dimensions of a few micrometers. This experimental technique, however, has only recently been applied to molecular crystals. Key differences between the application of this technique to molecular crystals and metals and other inorganics are identified. From this, protocols for the measurement of hardness and elastic modulus of molecular crystals of pharmaceutical interest are proposed. Using form I aspirin as a model system, the impact of single crystal sample surface preparation (washing and cleaving) on the surface roughness is explored. We show the importance of using a calibration sample with hardness and stiffness close to that of molecular crystals for the acquisition of more accurate data. The issue of solvent occlusions formed during crystal growth is discussed as a source of material property variation as well as tip contamination. It is proposed that this in part explains the significantly larger variation of the measured mechanical properties among different single crystals compared to those performed on a unique sample. Because both the indentation modulus and the hardness can vary significantly for low depth indents, samples were tested over a wide range of depths, which revealed that a minimum depth of penetration is required for the acquisition of data. This experiment is crucial and needs to be carried out for every system under study since it allows for the determination of the minimum-working load. Post-indentation imaging combined with crystallographic analysis and molecular simulations allows for the characterization and rationalization of the material plastic deformation mechanisms.

The Role of Cocrystallization-Mediated Altered Crystallographic Properties on the Tabletability of Rivaroxaban and Malonic Acid

The present work aims to understand the crystallographic basis of the mechanical behavior of rivaroxaban-malonic acid cocrystal (RIV-MAL Co) in comparison to its parent constituents, i.e., rivaroxaban (RIV) and malonic acid (MAL). The mechanical behavior was evaluated at the bulk level by performing “out of die” bulk compaction and at the particle level by nanoindentation. The tabletability order for the three solids was MAL < RIV < RIV-MAL Co. MAL demonstrated “lower” tabletability because of its lower plasticity, despite it having reasonably good bonding strength (BS). The absence of a slip plane and “intermediate” BS contributed to this behavior. The “intermediate” tabletability of RIV was primarily attributed to the differential surface topologies of the slip planes. The presence of a primary slip plane (0 1 1) with flat-layered topology can favor the plastic deformation of RIV, whereas the corrugated topology of secondary slip planes (1 0 2) could adversely affect the plasticity. In addition, the higher elastic recovery of RIV crystal also contributed to its tabletability. The significantly “higher” tabletability of RIV-MAL Co among the three molecular solids was the result of its higher plasticity and BS. Flat-layered topology slip across the (0 0 1) plane, the higher degree of intermolecular interactions, and the larger separation between adjacent crystallographic layers contributed to improved mechanical behavior of RIV-MAL Co. Interestingly, a particle level deformation parameter H/E (i.e., ratio of mechanical hardness H to elastic modulus E) was found to inversely correlate with a bulk level deformation parameter σ₀ (i.e., tensile strength at zero porosity). The present study highlighted the role of cocrystal crystallographic properties in improving the tabletability of materials.

Molecular Interpretation of the Compaction Performance and Mechanical Properties of Caffeine Cocrystals: A Polymorphic Study

The 1:1 caffeine (CAF) and 3-nitrobenzoic acid (NBA) cocrystal (CAF:NBA) displays polymorphism. Each polymorph shares the same docking synthon that connects individual CAF and NBA molecules within the asymmetric unit; however, the extended intermolecular interactions are significantly different between the two polymorphic modifications. These alternative interaction topologies translate to distinct structural motifs, mechanical properties, and compaction performance. To assist our molecular interpretation of the structure-mechanics-performance relationships for these cocrystal polymorphs, we combine powder Brillouin light scattering (p-BLS) to determine the mechanical properties with energy frameworks calculations to identify potentially available slip systems that may facilitate plastic deformation. The previously reported Form 1 for CAF:NBA adopts a 2D-layered crystal structure with a conventional 3.4 Å layer-to-layer separation distance. For Form 2, a columnar structure of 1D-tapes is displayed with CAF:NBA dimers running parallel to the (110) crystallographic direction. Consistent with the layered crystal structure, the shear modulus for Form 1 is significantly reduced relative to Form 2, and moreover, our p-BLS spectra for Form 1 clearly display the presence of low-velocity shear modes, which support the expectation of a low-energy slip system available for facile plastic deformation. Our energy frameworks calculations confirm that Form 1 displays a favorable slip system for plastic deformation. Combining our experimental and computational data indicates that the structural organization in Form 1 of CAF:NBA improves the compressibility and plasticity of the material, and from our tabletability studies, each of these contributions confers superior tableting performance to that of Form 1. Overall, mechanical and energy framework data permit a clear interpretation of the functional performance of polymorphic solids. This could serve as a robust screening approach for early pharmaceutical solid form selection and development.

Pseudosymmetric layers in high-Z′ and P1 structures of organic molecules

Layers having obvious approximate symmetry higher than that of the overall 3-D crystal are present in 20–25% of the Z′ > 4 and P1 organic structures archived in the Cambridge Structural Database. In some structures different types of layers alternate.

A digital workflow from crystallographic structure to single crystal particle attributes for predicting the formulation properties of terbutaline sulfate

A detailed inter-molecular (synthonic) analysis of terbutaline sulfate, an ionic addition salt for inhalation drug formulation, is related to its crystal morphology, the surface chemistry of the habit faces and hence to its crystal surface energy.

Increasing the performance, trustworthiness and practical value of machine learning models: a case study predicting hydrogen bond network dimensionalities from molecular diagrams

The value of a hydrogen bond network prediction model was improved using a tool to increase prediction trust. Its accuracy could be improved up to 73% or 89% with the compromise that only 34% and 8% of the test examples could be predicted.

Intermolecular Interactions in Functional Crystalline Materials: From Data to Knowledge

Intermolecular interactions of organic, inorganic, and organometallic compounds are the key to many composition–structure and structure–property networks. In this review, some of these relations and the tools developed by the Cambridge Crystallographic Data Center (CCDC) to analyze them and design solid forms with desired properties are described. The potential of studies supported by the Cambridge Structural Database (CSD)-Materials tools for investigation of dynamic processes in crystals, for analysis of biologically active, high energy, optical, (electro)conductive, and other functional crystalline materials, and for the prediction of novel solid forms (polymorphs, co-crystals, solvates) are discussed. Besides, some unusual applications, the potential for further development and limitations of the CCDC software are reported.

New insights and innovation from a million crystal structures in the Cambridge Structural Database

The Cambridge Structural Database (CSD) is the world's largest and most comprehensive collection of organic, organometallic, and metal-organic crystal structure information. Analyses using the data have wide impact across the chemical sciences in allowing understanding of structural preferences. In this short review, we illustrate the more common methods by which CSD data influence molecular design. We show how more data could lead to more refined insights into the future using a simple example of trifluoromethylphenyl fragments, highlighting how with sufficient data one can build a reasonable model of geometric change in a chemical fragment with torsional rotation, and show some recent examples where the CSD has been used in conjunction with other methods to provide design ideas and more computationally tractable workflows for derivation of useful insights into structural design.

Plasticity enhancement in pharmaceutical drugs by water of crystallization: unusual slip planes

Khandavilli et al. [(2019), IUCrJ, 6, 630-634] show the superior plasticity in hydrates of the pharmaceutical drugs, pregabalin and gabapetin, compared with their anhydrous forms. The water in the structure is believed to act as a lubricating agent in the packing of hydrates, thus facilitating slippage of molecules in the plastic bending of the crystals under external mechanical stress.

A Million Crystal Structures: The Whole Is Greater than the Sum of Its Parts

The founding in 1965 of what is now called the Cambridge Structural Database (CSD) has reaped dividends in numerous and diverse areas of chemical research. Each of the million or so crystal structures in the database was solved for its own particular reason, but collected together, the structures can be reused to address a multitude of new problems. In this Review, which is focused mainly on the last 10 years, we chronicle the contribution of the CSD to research into molecular geometries, molecular interactions, and molecular assemblies and demonstrate its value in the design of biologically active molecules and the solid forms in which they are delivered. Its potential in other commercially relevant areas is described, including gas storage and delivery, thin films, and (opto)electronics. The CSD also aids the solution of new crystal structures. Because no scientific instrument is without shortcomings, the limitations of CSD research are assessed. We emphasize the importance of maintaining database quality: notwithstanding the arrival of big data and machine learning, it remains perilous to ignore the principle of garbage in, garbage out. Finally, we explain why the CSD must evolve with the world around it to ensure it remains fit for purpose in the years ahead.

The CSD Drug Subset: The Changing Chemistry and Crystallography of Small Molecule Pharmaceuticals

We report the generation and statistical analysis of the CSD drug subset: a subset of the Cambridge Structural Database (CSD) consisting of every published small-molecule crystal structure containing an approved drug molecule. By making use of InChI matching, a CSD Python API workflow to link CSD entries to the online database Drugbank.ca has been produced. This has resulted in a subset of 8632 crystal structures, representing all published solid forms of 785 unique drug molecules. We hope that this new resource will lead to improvements in targeted cheminformatics and statistical model building in a pharmaceutical setting. In addition to this, as part of the Advanced Digital Design of Pharmaceutical Therapeutics collaboration between academia and industry, we have been given the unique opportunity to run comparative analysis on the internal crystal structure databases of AstraZeneca and Pfizer, alongside comparison to the CSD as a whole.