Jason B. Benedict

Molecular engineering of nanoscale order in organic electro-optic glasses

The rational design of bulk nanoscale order in organic electro-optic materials, where the strong dipole–dipole interactions tend to dominate over the weaker forces exploited for self-assembly processes, remains an attractive yet elusive goal. Towards this end, a series of pseudo-discotic dipolar nonlinear optical chromophores have been synthesized and fully characterized. Theoretical guidance and an iterative molecular design process have succeeded in engineering long-range nanoscale order in organic electro-optic glasses. Small-angle thin-film X-ray diffraction experiments demonstrate a self-assembled lamellar morphology in a majority of these materials. Cryogenic crystallography, using a synchrotron X-ray source, afforded the structure of a representative system. This structure, in concert with thin-film X-ray diffraction, atomic force microscopy, UV-vis-NIR absorption spectroscopy, and refractive index experiments elucidated the nanoscale order in the films. Application of these materials in electro-optics is discussed.

How does cyanide inhibit superoxide reductase?Insight from synthetic FeIIIN4S model complexes

Superoxide reductases (SORs) are nonheme iron-containing enzymes that reduce HO2 to H2O2. Exogenous substrates such as Ndocumentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} setlength{oddsidemargin}{-69pt} begin{document} begin{equation*}_{3}^{-}end{equation*}end{document} and CN− have been shown to bind to the catalytic iron site of SOR, and cyanide acts as an inhibitor. To understand how these exogenous ligands alter the physical and reactivity properties of the SOR iron site, acetate-, azide-, and cyanide-ligated synthetic models of SOR have been prepared. The x-ray crystal structures of azide-ligated [FeIII(SMe2N4(tren))(N3)]+ (3), dimeric cyanide-bridged ([FeIII(SMe2N4(tren))]2-μ-CN)3+ (5), and acetate-ligated [FeIII(SMe2N4(tren))(OAc)]+ (6) are described, in addition to x-ray absorption spectrum-derived and preliminary crystallographic structures of cyanide-ligated [FeIII(SMe2N4(tren))(CN)]+ (4). Cyanide coordination to our model (4) causes the redox potential to shift anodically by 470 mV relative to acetate-ligated 6 and 395 mV relative to azide-ligated 3. If cyanide coordination were to cause a similar shift in redox potential with SOR, then the reduction potential of the catalytically active Fe3+ center would fall well below that of its biological reductants. These results suggest therefore that cyanide inhibits SOR activity by making the Fe2+ state inaccessible and thus preventing the enzyme from turning over. Cyanide inhibits activity in the metalloenzyme superoxide dismutase via a similar mechanism. The reduced five-coordinate precursor to 3, 4, and 6 [FeII(SMe2N4(tren))]+ (1) was previously shown by us to react with superoxide to afford H2O2 via an [FeIII(SMe2N4(tren))(OOH)]+ intermediate. Cyanide and azide do not bind to 1 and do not prevent 1 from reducing superoxide.

Photochromism of a spirooxazine in the single crystalline phase.

The single crystals of a closed form spirooxazine spiro[azahomoadamantane-isoquinolinoxazine] were found for the first time to undergo photocoloration processes consistent with photochromism in the single crystalline phase.

Orientational dependence of linear dichroism exemplified by dyed spherulites.

D-sorbitol forms so-called spherulites from under-cooled melts. These polycrystalline formations have optically uniaxial radii. Melts pressed between glasses crystallize as plane sections of spheres. Dyes that are soluble in molten sorbitol become oriented as the crystallization front passes through the melt so as to form disks with large linear dichroism in the absorption bands of the dyes. The dyeing of spherulites is thus a general method of solute alignment. The linear optical properties of sorbitol spherulites containing the azo dye amaranth were analyzed in detail so as to correct a persistent confusion in the literature regarding the orientational dependence of linear dichroism. In cases involving thin film dichroism of multilayered samples requiring many corrections of intensity data in non-normal incidence, some authors have taken transmittance and others absorbance as having a cosine-squared angular dependence on the plane of the electric vector of linearly polarized light. Plane sections of doped spherulites present all orientations of an electric dipole oscillator in spatially localized region in normal incidence. As such, the samples described herein are ideally suited to resolving this confusion. Images of transmittance of dyed spherulites in polarized light were recorded with a CCD camera and simulated under the assumption that both absorbance and transmittance show a cosine-squared angular dependence but with respect to different angles. Transmittance with a cosine-squared dependence follows azimuthal rotations of the spherulite radii around the wave vector, while absorbance with a cosine-squared dependence follows rotations about axes perpendicular to the wave vector, natural consequences of the properties of the optical indicatrix that are often overlooked. Spherulites obviate the substantial experimental complexities that are engendered in non-normal incidence by sample reorientation. Thus, the principles of anisotropic absorption are given in a complete and intuitive fashion.

Potassium hydrogen diphthalate dihydrate: a new structure and correction to the literature.

The title compound, K(+).[(C(8)H(5)O(4))(2)H](-).2H(2)O or K(+).C(16)H(11)O(8)(-).2H(2)O, was prepared by slow evaporation of an aqueous solution of potassium hydrogen phthalate. The molecular complex consists of a potassium cation coordinated to a proton-bound hydrogen phthalate dimer and two water molecules. The potassium cation resides on a twofold axis in a distorted square-antiprism coordination geometry. The compound is isomorphous with the ammonium analogue, previously misidentified. As potassium hydrogen phthalate is frequently used in the manufacture of buffers, organic carbon standards, acidimetric standards and various other products, the crystallization of a compound with a different stoichiometery from a solution containing the acidimetric standard has important practical implications.

3,3′-Di­decyl-5,5′-bis(4-phenyl­quinolin-2-yl)-2,2′-bithienyl

The structure of the title compound, C58H64N2S2, is primarily dictated by intermolecular van der Waals interactions of the dixaddecyl chains attached to the bixadthioxadphene backbone. These interactions result in torsional strain on the aromatic plane, which disrupts conjugation.

Time-resolved EPR spectra of the triplet excited states of diaminoacridine guests in polar potassium hydrogen phthalate single crystals

Mixed crystals of potassium hydrogen phthalate containing 3,6-diaminoacridine were photoexcited with visible light and the resulting triplet excited states were analyzed by time resolved EPR spectroscopy. Spectra from discrete growth sectors were compared with powders and polycrystalline glasses prepared at various pHs. The data yield the predominant protonation state and orientation of the triplets in each of a pair of growth sectors bounding the positive and negative ends of the polar crystal.