Solid-State [4+4] Cycloaddition and Cycloreversion with Use of Unpaired Hydrogen-Bond Donors to Achieve Solvatomorphism and Stabilization

The crystal structure of a commercially available anthracene derivative, anthracene-9-thiocarboxamide, is reported here for the first time. The compound undergoes a [4+4] cycloaddition in the solid state to afford facile synthesis of the cycloadduct (CA). The cycloaddition is also reversible in the solid state using heat or mechanical force. Due to the presence of unpaired, strong hydrogen-bond donor atoms on the CA, significant solvatomorphism is achieved, and components of the solvatomorphs self-assemble into four different classes of supramolecular structures. The CA readily crystallizes with a variety of structurally-diverse solvents including those containing oxygen-, nitrogen-, or pi-acceptors. Some of the solvents the CA crystallized with include thiophene, benzene, and the three xylene isomers; thus, the CA was employed in industrially-relevant solvent separation. However, in competition studies, the CA did not exhibit selectivity. Lastly, it is demonstrated that the CA crystallizes with vinyl-containing monomers and is currently the only compound that crystallizes with both widely used monomers 4-vinylpyridine and styrene. Solid-state complexation of the CA with the monomers affords over a 50 °C increase in the monomer's thermal stabilities. The strategy of designing molecules with unused donors can be applied to achieve separations or volatile liquid stabilization.

Predicting photoactivity in dithienylethene crystalline solids

This commentary discusses the design of stimuli-responsive materials, specifically, light-responsive dithienylethene-based compounds. Recent progress in predicting photoactivity using a combination of theory and crystal structure landscape experiments is highlighted.

Dosimetric Advantages of VMAT TBI Plans: A Direct Comparison to Conventional TBI Plans

PURPOSE/OBJECTIVE(S)

Total body irradiation (TBI) continues to play an integral role in the conditioning of patients undergoing bone marrow transplantation. Historically, conventional TBI (C-TBI) has been delivered based on a clinical plan without CT simulation. However, volumetric modulated arc therapy TBI (V-TBI) is emerging as an alternative method to deliver TBI in a contemporary fashion. We aimed to compare these two methods of TBI delivery.

MATERIALS/METHODS

Patients undergoing treatment with V-TBI were identified. C-TBI plans were created using their existing simulation CT images. Patient thickness was measured on the scan and compensators such as lead sheets to attenuate dose in areas with less separation and lung blocks drawn on digitally reconstructed radiographs (DRR) were added when necessary. A 3D dose distribution was then calculated allowing for the direct comparison between C-TBI and V-TBI on the same patient using the same CT image set. Dosimetric data from each plan including target volume coverage, dose homogeneity, absolute max dose, and dose to lungs were recorded.

RESULTS

V-TBI and C-TBI plans for a total of four patients were preliminarily analyzed. Two patients were prescribed 200 cGy in a single fraction, while the other two were prescribed 1200 cGy in eight fractions. V-TBI resulted in a more favorable dosimetry for all four patients in most evaluated metrics including dose coverage, dose homogeneity, and lung dose (Table 1). V-TBI did result in an increased absolute maximum dose to all four patients compared to c-TBI, but still met the desired constraint of D0.03cc<125%.

CONCLUSION

V-TBI resulted in more favorable dosimetry for all four patients compared to C-TBI. To our knowledge, this is the first direct dosimetric comparison between the two methods. Analysis of 8 more V-TBI cases is currently underway. In the future, we plan to design a prospective study to evaluate the clinical outcomes of patients undergoing V-TBI vs C-TBI.

Colossal Anisotropic Thermal Expansion in a Diazo-Functionalized Compound with Switchable Solid-State Behavior

Achieving substantial anisotropic thermal expansion (TE) in solid-state materials is challenging as most materials undergo volumetric expansion upon heating. Here, we describe colossal, anisotropic TE in crystals of an organic compound functionalized with two azo groups. Interestingly, the material exhibits distinct and switchable TE behaviors within different temperature regions. At high temperature, two-dimensional, area zero TE and colossal, positive linear TE (α = 211 MK-1) are attained due to dynamic motion, while at low temperature, moderate positive TE occurs in all directions. Investigation of the solid-state motion showed the change in enthalpy and entropy are quite different in the two temperature regions and solid-state NMR experiments support motion in the solid. Cycling experiments demonstrate that the solid-state motions and TE behaviors are completely reversible. These results reveal strategies for designing significant anisotropic and switchable behaviors in solid-state materials.

Reversible interconversion of pharmaceutical salt polymorphs facilitated by mechanical methods

Salification of the drug trimethoprim with enantiopure D- or L-lactic acid afforded salts with up to five times improved solubility. Both salts are polymorphic and we demonstrate fully reversible interconversion (cycling) between the drug polymorphs using mechanochemistry and slurry methods. We show drug polymorph interconversion requires both solvent contact and mechanical force, revealing strategies for cycling between solid material forms.

Improved Syntheses of 4'-Vinylbenzo-3n-Crown-n Ethers (n = 5-7)

A convenient, high-yielding, and scalable synthetic approach to the construction of 4'-vinylbenzocrown ethers has been developed, which employs a decarboxylation and cyclization strategy. Using this method, a wide-ranging class of vinylbenzocrown ethers can be efficiently obtained. The identity of the crown ethers was further established using single-crystal X-ray diffraction studies. Two of the vinylbenzocrown ethers crystallize with water, affording infinite supramolecular assemblies containing hydrogen-bonded water molecules.

Controlling Thermal Expansion in Supramolecular Halogen-Bonded Mixed Cocrystals through Synthetic Feed and Dynamic Motion

Control over thermal expansion (TE) behaviors in solid materials is often accomplished by modifying the molecules or intermolecular interactions within the solid. Here, we use a mixed cocrystal approach and incorporate molecules with similar chemical structures, but distinct functionalities. Development of mixed cocrystals is at a nascent stage, and here we describe the first mixed cocrystals sustained by one-dimensional halogen bonds. Within each mixed cocrystal, the halogen-bond donor is fixed, while the halogen-bond acceptor site contains two molecules in a variable ratio. X-ray diffraction demonstrates isostructurality across the series, and SEM-EDS shows equal distribution of heavy atoms and similar atomic compositions across all mixed cocrystals. The acceptor molecules differ in their ability to undergo dynamic motion in the solid state. The synthetic equivalents of motion capable and incapable molecules were systematically varied to yield direct tunabililty in TE behavior.

Managing research throughout COVID-19: Lived experiences of supramolecular chemists

The international Women in Supramolecular Chemistry network believes that taking an area-specific approach effectively supports equality, diversity, and inclusion. Science lacks diversity, and this is intersectional. We share effects of coronavirus disease 2019 (COVID-19) by triangulating findings from an online survey, a collaborative autoethnography, and reflective group research meetings. We show how qualitative research with the community offers insights into challenges and supports individuals, and we demonstrate that research leaders have often taken responsibility for their teams' mental health and well-being at the cost of their own.

Removal of the Micropollutants Propranolol Hydrochloride and 2-Naphthol From Water by Pyridine-Functionalized Polymers

The number and concentration of micropollutants in aqueous environments are increasing. Two such micropollutants include the pharmaceutical, propranolol hydrochloride, and dye intermediate, 2-naphthol. Here, we describe the synthesis of both linear and crosslinked pyridine-functionalized copolymers that bind and remove propranolol hydrochloride and 2-naphthol from water solutions. Propranolol hydrochloride and 2-naphthol both contain hydrogen-bond-donor groups, and the pyridine moiety on the polymer acts as a hydrogen-bond acceptor to facilitate removal. Copolymers with different amounts of pyridine comonomer are synthesized, and as the amount of the pyridine comonomer is increased, the ability of the polymer to bind and remove the contaminant also increases. The concentrations of propranolol hydrochloride and 2-naphthol decreased by approximately 20–40% and 60–88%, respectively, depending on the polymer type that is used in the binding experiment. A control polymer was synthesized by using styrene in place of the pyridine monomer. In analogous binding experiments, the styrene polymer decreases the concentration of propranolol hydrochloride by 2% and 2-naphthol by 26%. Thus, the binding effectiveness is significantly reduced when the hydrogen-bond-acceptor group is not present on the polymer. We also show that the best performing crosslinked pyridine-functionalized polymer is reusable. Overall, these polymer adsorbents demonstrate the potential for removal of micropollutants from water.

Use of a Diels–Alder reaction to modify thermal expansion properties in charge-transfer cocrystals

A strategy for modifying thermal expansion properties in dichroic, charge-transfer cocrystals is described.

Differences in thermal expansion and motion ability for herringbone and face-to-face π-stacked solids

A series of aromatic organic molecules functionalized with different halogen atoms (I/ Br), motion-capable groups (olefin, azo or imine) and molecular length were designed and synthesized. The molecules self-assemble in the solid state through halogen bonding and exhibit molecular packing sustained by either herringbone or face-to-face π-stacking, two common motifs in organic semiconductor molecules. Interestingly, dynamic pedal motion is only achieved in solids with herringbone packing. On average, solids with herringbone packing exhibit larger thermal expansion within the halogen-bonded sheets due to motion occurrence and molecular twisting, whereas molecules with face-to-face π-stacking do not undergo motion or twisting. Thermal expansion along the π-stacked direction is surprisingly similar, but slightly larger for the face-to-face π-stacked solids due to larger changes in π-stacking distances with temperature changes. The results speak to the importance of crystal packing and intermolecular interaction strength when designing aromatic-based solids for organic electronics applications.

Thermal Expansion Properties and Mechanochemical Synthesis of Stoichiometric Cocrystals Containing Tetrabromobenzene as a Hydrogen- and Halogen-Bond Donor

The solution and mechanochemical synthesis of two cocrystals that differ in the stoichiometric ratio of the components (stoichiometric cocrystals) is reported. The components in the stoichiometric cocrystals interact through hydrogen or hydrogen/halogen bonds and differ in π-stacking arrangements. The difference in structure and noncovalent interactions affords dramatically different thermal expansion behaviors in the two cocrystals. At certain molar ratios, the cocrystals are obtained concomitantly; however, by varying the ratios, a single stoichiometric cocrystal is achieved using mechanochemistry.

Positive thermal expansion facilitates the formation of argentophilic forces following an order–disorder phase transition

Variable-temperature studies of the 0D silver-based complex [Ag₂(CF₃SO₃)₂(4-SB)₄] reveal formation of argentophilic forces upon warming due to a phase transition.

Solid-state behaviors of imines: colossal biaxial positive thermal expansion, motion capability, and phase transitions

The torsional flexibility of imines affects solid-state packing and properties. Behaviors including colossal thermal expansion, pedal motion, and phase transitions in imine-containing solids are described.

Triple-Columned and Multiple-Layered 3D Polymers: Design, Synthesis, Aggregation-Induced Emission (AIE), and Computational Study

Conjugated polymers and oligomers have great potentials in various fields, especially in materials and biological sciences because of their intriguing electronic and optoelectronic properties. In recent years, the through-space conjugation system has emerged as a new assembled pattern of multidimensional polymers. Here, a novel series of structurally condensed multicolumn/multilayer 3D polymers and oligomers have been designed and synthesized through one-pot Suzuki polycondensation (SPC). The intramolecularly stacked arrangement of polymers can be supported by either X-ray structural analysis or computational analysis. In all cases, polymers were obtained with modest to good yields, as determined by GPC and ¹H-NMR. MALDI-TOF analysis has proven the speculation of the step-growth process of this polymerization. The computational study of ab initio and DFT calculations based on trimer and pentamer models gives details of the structures and the electronic transition. Experimental results of optical and AIE research confirmed by calculation indicates that the present work would facilitate the research and applications in materials.

Controlling thermal expansion within mixed cocrystals by tuning molecular motion capability

Thermal expansion behavior is tuned by incorporating motion-capable or -incapable molecules into organic solids.

Controlling thermal expansion (TE) behaviors of organic materials is challenging because several mechanisms can govern TE, such as noncovalent interaction strength and structural motions. Here, we report the first demonstration of tuning TE within organic solids by using a mixed cocrystal approach. The mixed cocrystals contain three unique molecules, two of which are present in variable ratios. These two molecules either lack or exhibit the ability to undergo molecular motion in the solid state. Incorporation of higher ratios of motion-capable molecules results in larger, positive TE along the motion direction. Addition of a motion-incapable molecule affords solids that undergo less TE. Fine-tuned TE behavior was attained by systematically controlling the ratio of motion-capable and -incapable molecules in each solid.

Cambiarenes: Single-Step Synthesis and Selective Zwitterion Binding of a Clip-Shaped Macrocycle with a Redox-Active Core

A novel macrocyclic host molecule was synthesized that forms in a single step from commercially available starting materials. The core of the macrocycle backbone possesses two quinone rings and, thus, it is redox-active. Host-guest binding involving the clip-shaped cavity indicates selective binding of pyridine N-oxides based on the electron density of and steric bulk around the anionic oxygen.

Unique supramolecular complex of diclofenac: structural robustness, crystal-to-crystal solvent exchange, and mechanochemical synthesis

We describe an unexpected, cyclic supramolecular complex that results from self-assembly of the nonsteroidal anti-inflammatory drug, diclofenac and 4,4'-azopyridine. The cycles self-assemble into 1D columns occupied by solvent, which can be removed at elevated temperatures (>100 °C) while retaining crystallinity. The complex exhibits solvent exchange ability that occurs through crystal-to-crystal transformations. Finally, the complex can be synthesized using mechanochemistry. Materials exhibiting the structural framework and robustness described here could be applied to removal of hazardous materials or undesirable solvents.

Effects of dynamic pedal motion and static disorder on thermal expansion within halogen-bonded co-crystals

Thermal expansion is investigated for halogen-bonded co-crystals containing molecules that exhibit dynamic motion, lack motion ability, or experience static disorder.

Remarkable decrease in stiffness of aspirin crystals upon reducing crystal size to nanoscale dimensions via sonochemistry

Nano-dimensional crystals of aspirin generated through sonochemistry exhibit Young's modulus values an order of magnitude softer than macro-dimensional crystals.

Cooling-rate dependent single-crystal-to-single-crystal phase transition in an organic co-crystal

A reversible single-crystal-to-single-crystal phase transition is achieved via slow cooling; flash cooling locks the crystal in a kinetically trapped phase.

Functional materials based on molecules with hydrogen-bonding ability: applications to drug co-crystals and polymer complexes

The design, synthesis and property characterization of new functional materials has garnered interest in a variety of fields. Materials that are capable of recognizing and binding with small molecules have applications in sensing, sequestration, delivery and property modification. Specifically, recognition of pharmaceutical compounds is of interest in each of the aforementioned application areas. Numerous pharmaceutical compounds comprise functional groups that are capable of engaging in hydrogen-bonding interactions; thus, materials that are able to act as hydrogen-bond receptors are of significant interest for these applications. In this review, we highlight some crystalline and polymeric materials that recognize and engage in hydrogen-bonding interactions with pharmaceuticals or small biomolecules. Moreover, as pharmaceuticals often exhibit multiple hydrogen-bonding sites, many donor/acceptor molecules have been specifically designed to interact with the drug via such multiple-point hydrogen bonds. The formation of multiple hydrogen bonds not only increases the strength of the interaction but also affords unique hydrogen-bonded architectures.

Co-crystallization of anti-inflammatory pharmaceutical contaminants and rare carboxylic acid–pyridine supramolecular synthon breakdown

Co-crystallization of the pharmaceutical contaminants mefenamic acid and naproxen is reported; one co-crystal exhibits a rare carboxylic acid–pyridine synthon breakdown.

Thermal expansion along one-dimensional chains and two-dimensional sheets within co-crystals based on halogen or hydrogen bonds

Co-crystals assembled via halogen or hydrogen bonds yield minimal thermal expansion along 1D chains and greater expansion in 2D sheets.

Covalent bond formation via a [2+2] cycloaddition reaction as a tool to alter thermal expansion parameters of organic co-crystals

The thermal expansion properties of a co-crystal before and after undergoing a covalent-bond-generating reaction are discussed.

Polymerization Initiated by Particle Contact: A Quiescent State Trigger for Materials Synthesis

Dispersions of particles onto which reactive groups are bound give rise to inhomogeneous concentrations that may afford fundamentally different chemical behavior compared to the same molecular species dissolved in homogeneous solution. An example is bimolecular reactivity of complementary-functionalized particles, whereby interparticle contact is expected to promote fast kinetics localized to the interface, while exhibiting essentially no reactivity elsewhere. Such materials may exhibit unique properties analogous to blood clotting and thereby be useful in self-healing applications. Here, we demonstrate a radical polymerization reaction whose initiation is controlled by the physical proximity of two complementary co-initiators bound to a substrate and/or polymer beads. Polymerization of the surrounding acrylate monomer only occurs when interfaces functionalized with dimethylaniline encounter interfaces bearing benzoyl peroxide. At the interface of the complementary-functionalized beads, polymerization affords a "clot-like" scaffold of beads and polymer. Interestingly, such a scaffold is only attained when the beads are in a quiescent state. These findings open the way to the design of spatially controlled dual initiator systems and novel self-healing strategies and motifs.

Achieving dynamic behaviour and thermal expansion in the organic solid state via co-crystallization

Molecular motion of an azo functional group is ‘unlocked’ via co-crystallizations.

Thermal expansion involves a response of a material to an external stimulus that typically involves an increase in a crystallographic axis (positive thermal expansion (PTE)), although shrinking with applied heat (negative thermal expansion (NTE)) is known in rarer cases. Here, we demonstrate a means to achieve dynamic molecular motion and thermal expansions in organic solids via co-crystallizations. One co-crystal component is known to exhibit dynamic behaviour in the solid state while the second, when varied systematically, affords co-crystals with linear thermal expansion coefficients that range from colossal to nearly zero. Two co-crystals exhibit rare NTE. We expect the approach to guide the design of molecular solids that enable predesigned motion related to thermal expansion processes.

Head-to-tail photodimerization of a thiophene in a co-crystal and a rare adipic acid dimer in the presence of a heterosynthon

Head-to-tail photodimerization of thiophene is achieved in a co-crystal while a co-crystal with an acid dimer and heterosynthon is also described.

Gypsum mixtures for compensator construction

The characteristics and properties of a new material used for the fabrication of compensators are presented. This material is a special, refined gypsum. It requires a factor of 3 less water to prepare than ordinary gypsums and as a result the attenuation properties are stable over time. The material may be used by itself or mixed with fine metal particles to increase the attenuation per unit thickness. Gypsum, gypsum + steel, and gypsum + iron were investigated. The results of attenuation measurements in narrow- and broad-beam geometries appropriate to design of clinical dose modifying compensators are presented. Practical and technical details associated with the use of these materials are given. These compounds are found to be easy to use, versatile, reliable, environmentally safe, and inexpensive. In addition, an example of their use for dose compensation is given.