Cell-specific extracellular vesicle-encapsulated exogenous GABA controls seizures in epilepsy

BACKGROUND

Epilepsy affects ∼60 million people worldwide. Most antiseizure medications in the market act on voltage-gated sodium or calcium channels, indirectly modulating neurotransmitter GABA or glutamate levels or multiple targets. Earlier studies made significant efforts to directly deliver GABA into the brain with varied success. Herein, we have hypothesized to directly deliver exogenous GABA to the brain with epilepsy through extracellular vesicles (EVs) from human GABA-producing cells and their progenitors as EVs largely mimic their parent cell composition.

METHODS

Human neural stem cells (NSCs), medial ganglionic eminence (MGE) cells, and GABAergic interneurons (INs) were generated from induced pluripotent stem cells (iPSCs) and characterized. EVs were isolated from NSCs, MGE cells, and INs and characterized for size and distribution, morphological features, and molecular markers. Exogenous GABA was passively loaded to the isolated EVs as a zwitterion at physiological pH, and the encapsulated dose of GABA was quantified. Epilepsy was developed through status epilepticus induction in Fisher rats by administration of repeated low doses of kainic acid. The extent of the seizures was measured for 10 h/ day for 3-6 months by video recording and its evaluation for stage III, IV and V seizures as per Racine scale. EVs from INs, MGE cells, and NSCs encapsulated with exogenous GABA were sequentially tested in the 4th, 5th, and 6th months by intranasal administration in the rats with epilepsy for detailed seizure, behavioral and synapse analysis. In separate experiments, several controls including exogenic GABA alone and EVs from INs and MGE cells were evaluated for seizure-controlling ability.

RESULTS

Exogenic GABA could enter the brain through EVs. Treatment with EVs from INs and MGE cells encapsulated with GABA significantly reduced total seizures, stage V seizures, and total time spent in seizure activity. EVs from NSCs encapsulated with GABA demonstrated limited seizure control. Exogenic GABA alone and EVs from INs and MGE cells individually failed to control seizures. Further, exogenic GABA with EVs from MGE cells improved depressive behavior while partially improving memory functions. Co-localization studies confirmed exogenous GABA with presynaptic vesicles in the hippocampus, indicating the interaction of exogenous GABA in the brain with epilepsy.

CONCLUSION

For the first time, the study demonstrated that exogenous GABA could be delivered to the brain through brain cell-derived EVs, which could regulate seizures in temporal lobe epilepsy. It is identified that the cellular origin of EVs plays a vital role in seizure control with exogenous GABA.

The curious case of proton migration under pressure in the malonic acid and 4,4'-bipyridine cocrystal

In the search for new active pharmaceutical ingredients, the precise control of the chemistry of cocrystals becomes essential. One crucial step within this chemistry is proton migration between cocrystal coformers to form a salt, usually anticipated by the empirical ΔpKa rule. Due to the effective role it plays in modifying intermolecular distances and interactions, pressure adds a new dimension to the ΔpKa rule. Still, this variable has been scarcely applied to induce proton-transfer reactions within these systems. In our study, high-pressure X-ray diffraction and Raman spectroscopy experiments, supported by DFT calculations, reveal modifications to the protonation states of the 4,4'-bipyridine (BIPY) and malonic acid (MA) cocrystal (BIPYMA) that allow the conversion of the cocrystal phase into ionic salt polymorphs. On compression, neutral BIPYMA and monoprotonated (BIPYH+MA-) species coexist up to 3.1 GPa, where a phase transition to a structure of P21/c symmetry occurs, induced by a double proton-transfer reaction forming BIPYH22+MA2-. The low-pressure C2/c phase is recovered at 2.4 GPa on decompression, leading to a 0.7 GPa hysteresis pressure range. This is one of a few studies on proton transfer in multicomponent crystals that shows how susceptible the interconversion between differently charged species is to even slight pressure changes, and how the proton transfer can be a triggering factor leading to changes in the crystal symmetry. These new data, coupled with information from previous reports on proton-transfer reactions between coformers, extend the applicability of the ΔpKa rule incorporating the pressure required to induce salt formation.

Phase Transitions and Stabilities among Three Phases of Di-p-tolyl Disulfides

Di-p-tolyl disulfides (p-Tol₂S₂) are employed as load-carrying additives because of their anti-wear and extreme load-bearing qualities. External pressure triggers conformational up-conversion (leads to phase transition) in the molecules of p-Tol₂S₂, by compensating for the stress and absorbing its energy. These features make p-Tol₂S₂ a potential candidate for next-generation energy storage devices. Upon lithiation, MoS₂ expands up to 103% which causes stress and affects battery stability and performance. Therefore, it is essential to study these materials under different physical conditions. In this work, we used density functional theory (DFT) at ωB97XD/6-31G* functional level, to calculate lattice parameters, Gibbs free energies, and vibrational spectra of three phases (i.e., α, β, and γ) of p-Tol₂S₂ under different pressure and temperature conditions. The phase transition between phases α and β occurred at a pressure and temperature of 0.65 GPa and 463 K, respectively. Furthermore, phase transition between phases α and γ was found at a pressure and temperature of 0.35 GPa and 400 K, respectively. Moreover, no phase transition was observed between phases β and γ under the pressure range studied (0 GPa to 5.5 GPa). We also computed and compared the FT-IR spectra of the three phases. These results can guide scientists and chemists in designing more stable battery materials.

High-Pressure Polymorphs Nucleated and Stabilized by Rational Doping under Ambient Conditions

High-pressure polymorphs can be obtained and stabilized at ambient pressure by utilizing dopants with more voluminous molecules, inducing internal strain in the structures. This effect has been confirmed for doped resorcinol and imidazole derivatives by nucleating and stabilizing their high-pressure phases under ambient conditions. The dopant molecular volume and concentration, as well as the bulk modulus of the polymorph in the binary system, are related to the stability region in the single-component phase diagram. High-pressure isothermal and isochoric recrystallizations yielded pure single crystals of resorcinol ε above 0.20 GPa and a new polymorph ζ above 0.70 GPa. These recrystallizations of pure resorcinol revealed within 1 GPa of the p-T phase diagram the boundaries and the stability regions of four resorcinol polymorphs α, β, ε, and ζ, contrary to the compression experiments on ambient-pressure polymorphs α and β, when the high-pressure phases were hidden behind the wide hysteresis extending to nearly 5 GPa. The hysteresis, originating from the H-bonding networks, hinders the formation of polymorphs ε and ζ when polymorphs α and β are compressed without melting or dissolving the crystals. Polymorph ζ is the only known resorcinol structure built of hydrogen-bonded layers.

High-pressure Nucleation of Low-Density Polymorphs*

New polymorphs β and γ of bis-3-nitrophenyl disulphide, crystallized above 0.3 GPa, are less dense than the ambient-pressure polymorph α. This counterintuitive density relation results from the high-entropy nucleation and subsequent kinetic crystallization. The work performed by pressure compensates the high entropy and temperature product, substantiated in varied conformers and increased chemical potential. Pressure-increased viscosity promotes the kinetic polymorphs, in accordance with empirical Ostwald's rule of stages. It contrasts to mechanochemical techniques, favouring high-density polymorphs.

Structure-property relationships of molecular shape and orientation with compression and expansion of xylitol

Easy crystallization distinguishes xylitol from other sugars, which usually condense into a syrup from aqueous solution. Although two polymorphs, i.e. metastable monoclinic and high-density orthorhombic, have been reported for xylitol, only the latter is in practical use. Under high pressure, the same orthorhombic phase has been obtained by both isothermal and isochoric recrystallization. The stability of the orthorhombic xylitol phase to 5.0 GPa has been correlated with a uniform compression of all hydrogen bonds and some flexibility of the molecular conformation, which cushion the pressure-induced local strains. The anisotropic compressibility of xylitol and its thermal expansion are consistent with the rule of inverse effects of pressure and temperature. This inverse strain relationship has been correlated with the dimensions and orientation of xylitol molecules in the crystal structure.

A new monohydrated molecular salt of GABA with l-tartaric acid: the structure-forming role of water

A novel monohydrated molecular salt of GABA with l-tartaric acid was crystallized and investigated.

High-pressure preference for reduced water content in porous zinc aspartate hydrates

The zinc aspartate (ZnAsp2) complex, a common dietary supplement, preferentially crystallizes as the dihydrate (ZnAsp2·2H2O) from aqueous solution. Under normal conditions the dihydrate easily transforms into the sesquihydrate (ZnAsp2·1.5H2O). The dihydrate crystal structure is triclinic, space group P1, and the sesquihydrate is monoclinic, space group C2/c. However, their structures are closely related and similarly consist of zinc aspartate ribbons parallel to pores accommodating water molecules. These porous structures can breathe water molecules in and out depending on the temperature and air humidity. High pressure above 50 MPa favours the sesquihydrate, as shown by recrystallizations under pressure and compressibility measured by single-crystal X-ray diffraction up to 4 GPa. This preference is explained by the reduced volume of the sesquihydrate and water compressed separately, compared with the dihydrate. The sesquihydrate undergoes an isostructural phase transition when the voids collapse at 0.8 GPa, whereas no phase transitions occur in the dihydrate, because its pores are supported by increased water content.

Alloxan under pressure-squeezing an extremely dense molecular crystal structure

The crystal structure of the small organic molecule, alloxan, has been explored using high-pressure neutron diffraction; its already efficiently-packed structure provides a 'chemical head-start' on the pressure experiment. At the highest pressure measured, alloxan reaches a density of 2.36 g cm-3-unprecedented for a C, H(D), N, O-containing organic material of appreciable molecular weight. Its crystal structure is stable until ca. 6.5 GPa above which the sample starts to undergo amorphisation.

Lab in a DAC - high-pressure crystal chemistry in a diamond-anvil cell

The diamond-anvil cell (DAC) was invented 60 years ago, ushering in a new era for material sciences, extending research into the dimension of pressure. Most structural determinations and chemical research have been conducted at ambient pressure, i.e. the atmospheric pressure on Earth. However, modern experimental techniques are capable of generating pressure and temperature higher than those at the centre of Earth. Such extreme conditions can be used for obtaining unprecedented chemical compounds, but, most importantly, all fundamental phenomena can be viewed and understood from a broader perspective. This knowledge, in turn, is necessary for designing new generations of materials and applications, for example in the pharmaceutical industry or for obtaining super-hard materials. The high-pressure chambers in the DAC are already used for a considerable variety of experiments, such as chemical reactions, crystallizations, measurements of electric, dielectric and magnetic properties, transformations of biological materials as well as experiments on living tissue. Undoubtedly, more applications involving elevated pressure will follow. High-pressure methods become increasingly attractive, because they can reduce the sample volume and compress the intermolecular contacts to values unattainable by other methods, many times stronger than at low temperature. The compressed materials reveal new information about intermolecular interactions and new phases of single- and multi-component compounds can be obtained. At the same time, high-pressure techniques, and particularly those of X-ray diffraction using the DAC, have been considerably improved and many innovative developments implemented. Increasingly more equipment of in-house laboratories, as well as the instrumentation of beamlines at synchrotrons and thermal neutron sources are dedicated to high-pressure research.

Pressure-Induced Polymorphism of Caprolactam: A Neutron Diffraction Study

Caprolactam, a precursor to nylon-6 has been investigated as part of our studies into the polymerization of materials at high pressure. Single-crystal X-ray and neutron powder diffraction data have been used to explore the high-pressure phase behavior of caprolactam; two new high pressure solid forms were observed. The transition between each of the forms requires a substantial rearrangement of the molecules and we observe that the kinetic barrier to the conversion can aid retention of phases beyond their region of stability. Form II of caprolactam shows a small pressure region of stability between 0.5 GPa and 0.9 GPa with Form III being stable from 0.9 GPa to 5.4 GPa. The two high-pressure forms have a catemeric hydrogen-bonding pattern compared with the dimer interaction observed in ambient pressure Form I. The interaction between the chains has a marked effect on the directions of maximal compressibility in the structure. Neither of the high-pressure forms can be recovered to ambient pressure and there is no evidence of any polymerization occurring.

Antisolvent addition at extreme conditions

Antisolvent addition at high pressure (0.8 GPa) allows crystallization and recovery to ambient pressures of metastable form II paracetamol.

Discovery and recovery of delta p-aminobenzoic acid

A new high-pressure recoverable form has been observed in the model system, p-aminobenzoic acid.

Structural investigation and compression of a co-crystal of indomethacin and saccharin

Indomethacin : saccharin cocrystal has been studied under high pressure conditions and the amide interactions compared with previous high pressure studies.

A new copper(II) coordination polymer containing chains of interconnected paddle-wheel antiferromagnetic clusters

The construction of supramolecular architectures based on inorganic-organic coordination frameworks with weak noncovalent interactions has implications for the rational design of functional materials. A new crystalline binuclear copper(II) one-dimensional polymeric chain, namely catena-poly[[[tetrakis(μ-4-azaniumylbutanoato-κ²O:O')dicopper(II)(Cu-Cu)]-μ-chlorido-[diaquadichloridocopper(II)]-μ-chlorido] bis(perchlorate)], {[Cu₃Cl₄(C₄H₉NO₂)₄(H₂O)₂](ClO₄)₂}_n, was obtained by the reaction of 4-aminobutyric acid (GABA) with CuCl₂·2H₂O in aqueous solution. The structure was established by single-crystal X-ray diffraction and was also characterized by IR spectroscopy and magnetic measurements. The crystal structure consists of [{Cu₂(GABA)₄}{CuCl₄(H₂O)₂}]⁺ cations and isolated perchlorate anions. Two symmetry-related Cu^II centres are bridged via carboxylate O atoms into a classical paddle-wheel configuration, with a Cu...Cu distance of 2.643 (1) Å, while bridging Cl atoms complete the square-pyramidal geometry of the metal atoms. The Cl atoms connect the paddlewheel moieties to a second Cu^II atom lying on an octahedral site, resulting in infinite helical chains along the c axis. The packing motif exhibits channels containing free perchlorate anions. The crystal structure is stabilized by hydrogen bonds between the perchlorate anions, the coordinated water molecules and the ammonium groups of the polymeric chains. The magnetic analysis of the title compound indicates a nontrivial antiferromagnetic behaviour arising from alternating weak-strong antiferromagnetic coupling between neighbouring Cu^II centres.

Experimental and Computational Hydrate Screening: Cytosine, 5-Flucytosine and Their Solid Solution

The structural, temperature- and moisture dependent stability features of cytosine and 5-flucytosine monohydrates, two pharmaceutically important compounds, were rationalized using complementary experimental and computational approaches. Moisture sorption/desorption, water activity, thermal analysis and calorimetry were applied to determine the stability ranges of hydrate ↔ anhydrate systems, while X-ray diffraction, IR spectroscopy and crystal structure prediction provided the molecular level understanding. At 25 °C, the critical water activity for the cytosine hydrate ↔ anhydrate system is ~0.43 and for 5-flucytosine ~0.41. In 5-flucytosine the water molecules are arranged in open channels, therefore the kinetic desorption data, dehydration < 40% relative humidity (RH), conform with the thermodynamic data, whereas for the cytosine isolated site hydrate dehydration was observed at RH < 15%. Peritectic dissociation temperatures of the hydrates were measured to be 97 °C and 84.2 °C for cytosine and 5-flucytosine, respectively, and the monohydrate to anhydrate transition enthalpies to be around 10 kJ mol-1. Computed crystal energy landscapes not only revealed that the substitution of C5 (H or F) controls the packing and properties of cytosine/5-flucytosine solid forms, but also have enabled the finding of a monohydrate solid solution of the two substances which shows increased thermal- and moisture-dependent stability compared to 5-flucytosine monohydrate.

Pressure inverse solubility and polymorphism of an edible γ-cyclodextrin-based metal–organic framework

An edible metal–organic framework, γ-CD-MOF-1, has been obtained in a new trigonal form. The γ-CD-MOF-1 high-pressure dissolution as well as the cubic and trigonal polymorphs are closely related and regulated by the guest framework interactions and adsorption in the pores.

4-Aminoquinaldine monohydrate polymorphism: Prediction and impurity aided discovery of a difficult to access stable form

Crystal structure prediction studies indicated the existence of an unknown high density monohydrate structure (Hy1B°) as global energy minimum for 4-aminoquinaldine (4-AQ). We thus performed an interdisciplinary experimental and computational study elucidating the crystal structures, solid form inter-relationships, kinetic and thermodynamic stabilities of the stable anhydrate (AH I°), the kinetic monohydrate (Hy1A ) and this novel monohydrate polymorph (Hy1B°) of 4-AQ. The crystal structure of Hy1B° was determined by combining laboratory powder X-ray diffraction data and ab initio calculations. Dehydration studies with differential scanning calorimetry and solubility measurements confirmed the result of the lattice energy calculations, which identified Hy1B° as the thermodynamically most stable hydrate form. At 25 °C the equilibrium of the 4-AQ hydrate/anhydrate system was observed at an aw (water activity) of 0.14. The finding of Hy1B° was complicated by the fact that the metastable but kinetically stable Hy1A shows a higher nucleation and growth rate. The presence of an impurity in an available 4-AQ sample facilitated the nucleation of Hy1B°, whose crystallisation is favored under hydrothermal conditions. The value of combining experimental with theoretical studies in hydrate screening and characterisation, as well as the reasons for hydrate formation in 4-AQ, are discussed.

Computational and Experimental Characterization of Five Crystal Forms of Thymine: Packing Polymorphism, Polytypism/Disorder and Stoichiometric 0.8-Hydrate

New polymorphs of thymine emerged in an experimental search for solid forms, which was guided by the computationally generated crystal energy landscape. Three of the four anhydrates (AH) are homeoenergetic (A° - C) and their packing modes differ only in the location of oxygen and hydrogen atoms. AHs A° and B are ordered phases, whereas AH C shows disorder (X-ray diffuse scattering). Anhydrates AHs A° and B are ordered phases, whereas AH C shows disorder (X-ray diffuse scattering). Analysis of the crystal energy landscape for alternative AH C hydrogen bonded ribbon motifs identified a number of different packing modes, whose 3D structures were calculated to deviate by less than 0.24 kJ mol-1 in lattice energy. These structures provide models for stacking faults. The three anhydrates A° - C show strong similarity in their powder X-ray diffraction, thermoanalytical and spectroscopic (IR and Raman) characteristics. The already known anhydrate AH A° was identified as the thermodynamically most stable form at ambient conditions; AH B and AH C are metastable but show high kinetic stability. The hydrate of thymine is stable only at water activities (aw) > 0.95 at temperatures ≤ 25 °C. It was found to be a stoichiometric hydrate despite being a channel hydrate with an unusual water:thymine ratio of 0.8:1. Depending on the dehydration conditions, either AH C or AH D is obtained. The hydrate is the only known precursor to AH D. This study highlights the value and complementarity of simultaneous explorations of computationally and experimentally generated solid form landscapes of a small molecule anhydrate ↔ hydrate system.

High pressure used for producing a new solvate of 1,4-diazabicyclo[2.2.2]octane hydroiodide

Above 3.1 GPa, the solvate with water and methanol is formed, which cannot be obtained at normal pressure.

The role of fluids in high-pressure polymorphism of drugs: different behaviour of β-chlorpropamide in different inert gas and liquid media

Compression of β-chlorpropamide gives different phases depending on the choice of non-dissolving pressure-transmitting fluid (paraffin, neon and helium).

Giant strain geared to transformable H-bonded network in compressed β-d-mannose

The clearly visible shape change of β-d-mannose crystals is associated with pressure-induced isostructural phase transition.

Supramolecular interactions in the solid state

In the last few decades, supramolecular chemistry has been at the forefront of chemical research, with the aim of understanding chemistry beyond the covalent bond. Since the long-range periodicity in crystals is a product of the directionally specific short-range intermolecular interactions that are responsible for molecular assembly, analysis of crystalline solids provides a primary means to investigate intermolecular interactions and recognition phenomena. This article discusses some areas of contemporary research involving supramolecular interactions in the solid state. The topics covered are: (1) an overview and historical review of halogen bonding; (2) exploring non-ambient conditions to investigate intermolecular interactions in crystals; (3) the role of intermolecular interactions in morphotropy, being the link between isostructurality and polymorphism; (4) strategic realisation of kinetic coordination polymers by exploiting multi-interactive linker molecules. The discussion touches upon many of the prerequisites for controlled preparation and characterization of crystalline materials.

Combined crystal structure prediction and high-pressure crystallization in rational pharmaceutical polymorph screening

Organic molecules, such as pharmaceuticals, agro-chemicals and pigments, frequently form several crystal polymorphs with different physicochemical properties. Finding polymorphs has long been a purely experimental game of trial-and-error. Here we utilize in silico polymorph screening in combination with rationally planned crystallization experiments to study the polymorphism of the pharmaceutical compound Dalcetrapib, with 10 torsional degrees of freedom one of the most flexible molecules ever studied computationally. The experimental crystal polymorphs are found at the bottom of the calculated lattice energy landscape, and two predicted structures are identified as candidates for a missing, thermodynamically more stable polymorph. Pressure-dependent stability calculations suggested high pressure as a means to bring these polymorphs into existence. Subsequently, one of them could indeed be crystallized in the 0.02 to 0.50 GPa pressure range and was found to be metastable at ambient pressure, effectively derisking the appearance of a more stable polymorph during late-stage development of Dalcetrapib.

Crystal polymorphism can lead to substances with vastly differing physicochemical properties, which has serious implications in the pharmaceutical industry. Here, the authors use in silico polymorph screening to accurately predict the resulting structures under set crystallisation environments.

New method to compute Rcomplete enables maximum likelihood refinement for small datasets

The crystallographic reliability index [Formula: see text] is based on a method proposed more than two decades ago. Because its calculation is computationally expensive its use did not spread into the crystallographic community in favor of the cross-validation method known as [Formula: see text]. The importance of [Formula: see text] has grown beyond a pure validation tool. However, its application requires a sufficiently large dataset. In this work we assess the reliability of [Formula: see text] and we compare it with k-fold cross-validation, bootstrapping, and jackknifing. As opposed to proper cross-validation as realized with [Formula: see text], [Formula: see text] relies on a method of reducing bias from the structural model. We compare two different methods reducing model bias and question the widely spread notion that random parameter shifts are required for this purpose. We show that [Formula: see text] has as little statistical bias as [Formula: see text] with the benefit of a much smaller variance. Because the calculation of [Formula: see text] is based on the entire dataset instead of a small subset, it allows the estimation of maximum likelihood parameters even for small datasets. [Formula: see text] enables maximum likelihood-based refinement to be extended to virtually all areas of crystallographic structure determination including high-pressure studies, neutron diffraction studies, and datasets from free electron lasers.

Disappearing polymorphs revisited

Nearly twenty years ago, Dunitz and Bernstein described a selection of intriguing cases of polymorphs that disappear. The inability to obtain a crystal form that has previously been prepared is indeed a frustrating and potentially serious problem for solid-state scientists. This Review discusses recent occurrences and examples of disappearing polymorphs (as well as the emergence of elusive crystal forms) to demonstrate the enduring relevance of this troublesome, but always captivating, phenomenon in solid-state research. A number of these instances have been central issues in patent litigations. This Review, therefore, also highlights the complex relationship between crystal chemistry and the law.

High-pressure crystallography of periodic and aperiodic crystals

More than five decades have passed since the first single-crystal X-ray diffraction experiments at high pressure were performed. These studies were applied historically to geochemical processes occurring in the Earth and other planets, but high-pressure crystallography has spread across different fields of science including chemistry, physics, biology, materials science and pharmacy. With each passing year, high-pressure studies have become more precise and comprehensive because of the development of instrumentation and software, and the systems investigated have also become more complicated. Starting with crystals of simple minerals and inorganic compounds, the interests of researchers have shifted to complicated metal-organic frameworks, aperiodic crystals and quasicrystals, molecular crystals, and even proteins and viruses. Inspired by contributions to the microsymposium 'High-Pressure Crystallography of Periodic and Aperiodic Crystals' presented at the 23rd IUCr Congress and General Assembly, the authors have tried to summarize certain recent results of single-crystal studies of molecular and aperiodic structures under high pressure. While the selected contributions do not cover the whole spectrum of high-pressure research, they demonstrate the broad diversity of novel and fascinating results and may awaken the reader's interest in this topic.

Polymorphism of a polymer precursor: metastable glycolide polymorph recovered via large scale high-pressure experiments

Using a large volume high-pressure press a new polymorph of an important precursor for biomedical polymers was isolated in gram quantities and used to seed crystallisation experiments at ambient pressure.

Are gamma amino acids promising tools of crystal engineering? – Multicomponent crystals of baclofen

The crystal structure, thermal analysis and powder X-ray analysis of the multicomponent crystals formed between baclofen and selected monocarboxylic acids, dicarboxylic acids and p-toluene sulfonic acid are presented.

Accurate and Efficient Model Energies for Exploring Intermolecular Interactions in Molecular Crystals

The energy of interaction between molecules is commonly expressed in terms of four key components: electrostatic, polarization, dispersion, and exchange-repulsion. Using monomer wave functions to obtain accurate estimates of electrostatic, polarization, and repulsion energies along with Grimme's dispersion corrections, a series of energy models are derived by fitting to dispersion-corrected DFT energies for a large number of molecular pairs extracted from organic and inorganic molecular crystals. The best performing model reproduces B3LYP-D2/6-31G(d,p) counterpoise-corrected energies with a mean absolute deviation (MAD) of just over 1 kJ mol(-1) but in considerably less computation time. It also performs surprisingly well against benchmark CCSD(T)/CBS energies, with a MAD of 2.5 kJ mol(-1) for a combined data set including Hobza's X40, S22, A24, and S66 dimers. Two of these energy models, the most accurate and the fastest, are expected to find widespread application in investigations of molecular crystals.

processPIXEL: a program to generate energy-vector models from Gavezzotti'sPIXELcalculations

A command-line program is presented to convert the output from Gavezzotti'sPIXELcalculations to Shishkin's energy-vector models representing the intermolecular interaction topology. The output models comprise sets of vectors joining the centres of the molecules in a crystal structure, scaled so that the vector representing the most stabilizing pairwise interaction has length equal to half of the corresponding intermolecular separation. When the energy-vector model is packed, the most stabilizing pairwise interaction is represented as a continuous line between interacting molecules, while the other intermolecular interactions are shown as discontinuous lines, with a smaller gap representing a more stabilizing interaction. The energy-vector models can be overlaid on the crystal structure using theMercuryvisualizer to enable convenient visualization of structural motifs that contribute significantly to the overall crystal packing energy.