Dale C. Swenson

Softening and Hardening of Macro‐ and Nano‐Sized Organic Cocrystals in a Single‐Crystal Transformation

The structure and properties of organic solids have great potential for rational design by using the principles of organic chemistry and supramolecular synthesis. Understanding how to control the properties of organic solids, however, is a challenge owing to the sensitivity of close packing to subtle changes to molecular structure. 5] The reactivities of organic solids are of interest, especially those that undergo photoinduced single-crystal-to-single-crystal (SCSC) transformations. 7] Potential applications of solids that undergo SCSC reactions lie in pharmaceutical and materials science, supramolecular synthesis, and device applications, such as photoactivated molecular switches, 13] 3D data storage, and nanoscale photomechanical actuators. However, such promise is limited by a rarity of materials that undergo SCSC transformations. As photoirradiating a crystal will involve significant atomic motion, there is invariably an accumulation of stress and strain that causes crystals to crack and even crumble into a powder. Recent reports demonstrate that a SCSC reaction is possible in nanocrystals even when corresponding macrodimensional crystals do not display SCSC reactivity. 19,20] The possibility to induce SCSC reactions through miniaturizing crystals to nanodimensions can lead to the development of functional nanomaterials. The small size of nanocrystals can also result in physical and chemical properties that are different from macroscopic solids. The ability of nanocrystals to undergo photoinduced SCSC transformations can be attributed to a high surface-to-volume ratio that leads to more efficient stress and strain relaxation that is most likely absent for macrodimensional solids. The exact nature of the relaxation is, however, unknown. Surprisingly, while a relaxation mechanism can be considered to be inherently related to the mechanical properties of a reactive solid, mechanical properties of solids that undergo SCSC transformations have not been investigated. Mechanical properties also allow solid functionalities and allowable operating limits in device applications to be defined. Moreover, gaining knowledge of mechanical properties of crystals that undergo SCSC transformations will thus, in addition to technological applications, be no doubt critical to develop an understanding of strain relaxation mechanisms and possibly allow the prediction of reactive properties. Herein, we present a cocrystal 3] that undergoes a SCSC 7] transformation wherein the crystals undergo softening or hardening depending on size (Scheme 1). The

Relative importance of X?O?C vs. X?X halogen bonding as structural determinants in 4-halotriaroylbenzenes

The structures of 4-chloro- and 4-bromotribenzoylbenzene, as well as a solid solution prepared from these two components, are isomorphous and dominated by C-X...O=C interactions, whereas type-II I...I interactions are important in the 4-iodo derivative.

Nanocrystals of a Metal–Organic Complex Exhibit Remarkably High Conductivity that Increases in a Single-Crystal-to-Single-Crystal Transformation

Ag(I) is used to form a π-stacked metal-organic solid that exhibits remarkably high electrical conductivity. The solid undergoes a single-crystal-to-single-crystal [2+2] photodimerization to generate a 1D coordination polymer with over 40% higher conductivity. The Ag(I) complex represents the first example of an increase in conductivity resulting from a [2+2] photodimerization. Density of states calculations show a higher contribution from Ag(I) ions to the valence band in the photodimerized solid, supporting the increase in conductivity.

Molecular details of receptor binding and hormonal action of steroids derived from X-ray crystallographic investigations

Abstract Analysis of X-ray crystallographic data on steroids provides information concerning preferred conformations, relative stabilities, and substituent influence on the interactive potential of steroid hormones. Analysis of the data on the 4-ene-3-one ring indicates that it normally has a conformation midway between the 1α,2β-half chair and the 1α-sofa forms. Strain introduced into the molecule by substitution on the fused ring system shifts the A-ring conformation toward the more symmetric forms with an attendant change in the conjugation of the 4-ene-3-one system. Crystallographic data on 85 pregnane structures having a 20-one substituent provide information on 17β-side chain flexibility. In eighty-one structures the C(16)-C(17)-C(20)-O(20) torsion angle is between 0° and −46°. This is consistent with CD, i.r. and n.m.r. solution spectra and more precisely defines the side chain conformation in solution. The four structures whose side chains lie outside this range do so because of the presence of a 16β-substituent and not because of crystal packing forces. The steroid A ring appears to be primarily responsible for initiating and maintaining hormone binding to the estrogen and progestin receptors. When the structures of agonists and antagonists of specific steroid hormones are compared, they generally exhibit similarities in their A-ring region and dissimilarities in the D-ring region further suggesting that the steroid A-ring bears responsibility for receptor binding while the D-ring controls expression of activity. Antihormoncs that compete for the receptor site of a steroid hormone may be expected to have structural features appropriate for receptor binding (A-ring composition and conformation) and lack structural features that induce or stabilize subsequent receptor functions (D-ring conformatjonal features and functional groups).

Chaetochalasin A: A New Bioactive Metabolite from Chaetomium Brasiliense

Abstract Chaetochalasin A ( 1 ), a new bioactive fungal metabolite with a previously undescribed ring system, has been isolated from an EtOAc extract of Chaetomium brasiliense (NRRL 22999). The structure of 1 was determined by NMR experiments and single-crystal X-ray diffraction analysis.

Hexagonal crystalline inclusion complexes of 4-iodophenoxy trimesoate

Bifurcated Ipi and IO[double bond, length as m-dash]C halogen bonding interactions assist in formation of unique iodo-arene trimers leading to nanoscale channels in inclusion complexes of trimesic acid iodophenolate.

Conformational polymorphism in a heteromolecular single crystal leads to concerted movement akin to collective rack-and-pinion gears at the molecular level

We describe a heteromolecular single crystal that exhibits three reversible and concerted reorganizations upon heating and cooling. The products of the reorganizations are conformational polymorphs. The reorganizations are postulated to proceed through three motions: (i) alkyl translations, (ii) olefin rotations, and (iii) rotational tilts. The motions are akin to rack-and-pinion gears at the molecular level. The rack-like movement is based on expansions and compressions of alkyl chains that are coupled with pinion-like 180° rotations of olefins. To accommodate the movements, phenol and thiophene components undergo rotational tilts about intermolecular hydrogen bonds. The movements are collective, being propagated in close-packed repeating units. This discovery marks a step to understanding how organic solids can support the development of crystalline molecular machines and devices through correlated and collective movements.

Massarilactones A and B: novel secondary metabolites from the freshwater aquatic fungus Massarina tunicata

Abstract Massarilactones A and B ( 1 and 2 ) have been isolated from cultures of the freshwater aquatic fungus Massarina tunicata. The structures, including absolute stereochemistry, were determined by X-ray diffraction analysis of their bis(4-bromobenzoate) derivatives.

Botryolides A−E, Decarestrictine Analogues from a Fungicolous Botryotrichum sp. (NRRL 38180)⊥

Four new decarestrictine analogues (botryolides A-D; 1- 4), a biosynthetically related gamma-lactone (botryolide E; 5), and the known compounds decarestrictine D ( 6) and sterigmatocystin have been isolated from cultures of a fungicolous isolate of Botryotrichum sp. (NRRL 38180). The structures of these compounds were determined by analysis of 2D NMR and ESIMS data. The relative configurations of 1- 5 were established on the basis of NMR data and/or X-ray diffraction analysis, while the absolute configuration of 1 was assigned using the modified Mosher method.

Similins A and B : new antifungal metabolites from the coprophilous fungus Sporormiella similis

Abstract Similins A and B (2 and 3), two new metabolites from the coprophilous fungus Sporormiella similis , have been isolated and identified. Similin A was found to be responsible for the antifungal activity exhibited by S. similis . The relative stereochemistry of similin B was established by x-ray crystallography.