Kacey Claborn

Imaging linear birefringence and dichroism in cerebral amyloid pathologies.

New advances in polarized light microscopy were used to image Congo red-stained cerebral amyloidosis in sharp relief. The rotating-polarizer method was used to separate the optical effects of transmission, linear birefringence, extinction, linear dichroism, and orientation of the electric dipole transition moments and to display them as false-color maps. These effects are typically convolved in an ordinary polarized light microscope. In this way, we show that the amyloid deposits in Alzheimers disease plaques contain structurally disordered centers, providing clues to mechanisms of crystallization of amyloid in vivo. Comparisons are made with plaques from tissues of subjects having Downs syndrome and a prion disease. In plaques characteristic of each disease, the Congo red molecules are oriented radially. The optical orientation in amyloid deposited in blood vessels from subjects having cerebral amyloid angiopathy was 90° out of phase from that in the plaques, suggesting that the fibrils run tangentially with respect to the circumference of the blood vessels. Our result supports an early model in which Congo red molecules are aligned along the long fiber axis and is in contrast to the most recent binding models that are based on computation. This investigation illustrates that the latest methods for the optical analysis of heterogeneous substances are useful for in situ study of amyloid.

Polarimetric imaging of crystals

Classical crystal optics has recently undergone a renaissance as developments in optical microscopy and polarimetry, enabled in part by sensitive imaging CCD cameras and personal computers, now permit the analytical separation of various optical effects that are otherwise convolved in polarized light micrographs. In this tutorial review, we review recent developments in the measurement of the principal crystallo-optical quantities including linear birefringence, linear dichroism, circular birefringence, and circular dichroism, as well as new effects in crystal optics encountered in unusual mixed crystals. The new microscopies and polarimetries are applied to problems of crystallographic twinning, phase transformations, stress birefringence, symmetry reduction, and the design of new crystalline materials.

Structural Studies of 2,6-Diacetyl- and 2,6-Diformylpyridine Bis(thiosemicarbazones)

Although a large number of crystal structures of heterocyclic thiosemicarbazones have recently appeared in the literature, few structures of heterocyclic bis(thiosemicarbazones) or their metal complexes have been reported. Complexes of iron(II), indium(III), tin(IV), bismuth(III) involve bis(thiosemicarbazones) coordinating as N3S2 pentadentate ligands, often resulting in 7-coordinate complexes. In contrast, complexes with zinc(II) are often binuclear with thiosemicarbazone moieties of a bis(thiosemicarbazone) coordinating to two different zinc centers. Also included in this study is the structure of the first complex with a 2,6-diformylpyridine bis(thiosemicarbazone) ligand, a 4-coordinate nickel(II) complex with unusual coordination.

Calculations of optical properties of the tetraphenyl-X family of isomorphous crystals (X = C, Si, Ge, Sn, Pb)

As part of a program to determine how small structural changes become manifest in the optical properties of crystals we used classical dipole–dipole interaction calculations to estimate the linear birefringence and optical rotatory power of the crystals Ph4X where X = C, Si, Ge, Sn, and Pb. Field induced effects including second harmonic generation, the electro-optic response and electrogyration were calculated using the dipole electron shifting model (DES) model. The calculated induced effects are larger than those in standard materials such as KH2PO4. All of the properties tend to increase in magnitude with increasing polarizability except for optical rotation, which is largest for Ph4C. We propose an interpretation for the unusual behaviour of the optical rotation in terms of competing helical circuits of closely bonded atoms.

Structural, thermal and spectral studies of N-2-pyridyl-, N-2-picolyl- and N-2-(4,6-lutidyl)-N′-(3-methoxyphenyl)thioureas

Abstract N -2-pyridyl- N ′-3-methoxyphenylthiourea, PyTu3OMe, triclinic, P -l, a =8.6590(16), b =8.7489(16), c=10.0540(15) A , α =90.255(9), β =66.765(8), γ =68.547(7)°, V=641.40(19) A 3 and Z =2; N -2-(3-picolyl)- N ′-3-methoxyphenylthiourea, 3PicTu3OMe, triclinic, P -1, a =6.9100(9), b =12.7370(16), c=16.4710(14) A , α =107.782(6), β =91.656(7), γ =95.115(4)°, V=1372.5(3) A 3 and Z =4; N -2-(4-picolyl)- N ′-3-methoxphenylthiourea, 4PicTu3OMe, monoclinic, C 2/ c , a =12.5036(7), b =8.5942(5), c=25.4050(10) A , β =97.712(3)°, V=2705.3(2) A 3 and Z =8; N -2-(5-picolyl)- N ′-3-methoxyphenylthiourea, 5PicTu3OMe, monoclinic, P 2 1 / c , a =10.9200(4), b =15.3920(15), c=8.1150(11) A , β =92.020(5)°, V=1363.1(2) A 3 and Z =4; N -2-(6-picolyl)- N ′-3-methoxyphenylthiourea, 6PicTu4OMe, triclinic, P -1, a =7.4220(16), b =9.944(3), c=10.038(3) A , α =104.815(9), β =94.452(16), γ =108.134(14)°, V=670.6(3) A 3 and Z =2 and N -2-(4,6-lutidyl)- N ′-3-methoxyphenylthiourea, 4,6LutTu3OMe, orthorhombic, Pbca , a =16.3710(5), b =7.4910(6), c=24.1890(15) A , V =2966.4(3), Z =8. Intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding between NH and the thione sulfur are characteristic of these thioureas except that 3PicTu3OMe has a very weak intermolecular NH⋯S interaction due to a steric effect of the methyl group.

Structural, spectral and thermal studies of N-2-(picolyl)-N′-4-chlorophenylthioureas

Abstract N -2-(4-picolyl)- N ′-4-chlorophenylthiourea, 4PicTu4ClPh, triclinic, P -1, a =7.5235(3), b =9.1585(5), c=10.5158(7) A , α =76.015(3), β =70.015(4), γ =82.010(4)°, V=1309.8(2) A 3 and Z =2; N -2-(5-picolyl)- N ′-4-chlorophenylthiourea, 5PicTu4ClPh, monoclinic, P 2 1 / c , a =15.139(2), b =4.8386(3), c=17.338(2) A , β =90.661(4)°, V=1270.0(2) A 3 and Z =4 and N -2-(6-picolyl)- N ′-4-chlorophenylthiourea, 6PicTu4ClPh, monoclinic, C 2/ c , a =33.520(6), b =4.0750(3), c=18.658(4) A , β =97.500(6)°, V=2526.8(7) A 3 and Z =8. The most striking difference between the structures of the three thioureas is the difference in planarity, and among the four N -2-(picolyl)- N ′-4-chlorophenylthioureas, their values for Δ H fus .

Structural, spectral and thermal studies of N-2-(pyridyl)- and N-2-(picolyl)-N′-(3-chlorophenyl)thioureas

Abstract N-2-(pyridyl)-N′-3-chlorophenylthiourea, PyTu3Cl, monoclinic, P21, a=9.9770(14), b=6.1770(9), c=9.9000(7) A , β=97.301(8)°, V=605.17(13) A 3 and Z=2; N-2-(4-picolyl)-N′-3-chlorophenylthiourea, 4PicTu3Cl, triclinic, P−1, a=4.7970(3), b=10.7180(12), c=12.7370(15) A , α=77.919(4), β=85.959(6), γ=89.697(7)°, V=638.74(11) A 3 and Z=2; N-2-(5-picolyl)-N′-3-chlorophenylthiourea, 5PicTu3Cl, monoclinic, P21/c, a=11.1580(6), b=15.233(2), c=7.5118(15) A , β=93.336(8)°, V=1274.5(3) A 3 and Z=4 and N-2-(6-picolyl)-N′-3-chlorophenylthiourea, 6PicTu3Cl, triclinic, P−1, a=7.3620(12), b=8.828(3), c=11.675(3) A , α=98.78(1), β=104.398(17), γ=109.651(16)°, V=668.5(2) A 3 and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the presence and position of the methyl substituent on the pyridine ring. 1H NMR studies in CDCl3 show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra indicating intramolecular hydrogen bonding is also present in solution.