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 Alzheimer's 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 Down's 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.T he abnormal transformation of proteins to amyloid fibrils is closely related to the so-called conformational diseases that include the common neurodegenerative disorders such as Alzheimer's disease (AD) and prion diseases. The kinetic and structural bases of fibrillogenesis in these diseases are as yet undetermined. Nevertheless, the presence of amyloid in diseased tissues has been used for the purpose of pathological diagnosis and construction of theories of pathogenesis. A structural characterization and categorization of various forms of amyloid aid accurate diagnosis of amyloid disorders and further our mechanistic understanding of an increasing list of conformational diseases.The principal diagnostic criterion of amyloidosis, established by Divry and Florkin (1), is the detection with a polarizing optical microscope of so-called apple-green birefringence (2-6) from Congo red (CR)-stained tissue sections (7). Despite the durability of this assay, the optical characterization of amyloid has not progressed and is ambiguous (8, 9). The birefringence is rarely quantified, a problem further confounded by the fact that CR does not stain amyloid consistently, and diagnosis by staining depends on the skill of the investigator. Clearly, new opticalcontrast mechanisms are required for simple, reliable amyloid diagnosis (10, 11).Here, we show that recent advances in polarized light microscopy can be used to quickly quantify and refine our description of CR-stained amyloid. In particular, we applied a newly developed imaging system to separate the optical transmission, refractive index anisotropy [linear birefringence (LB)], and optic...

Fingerprint plots of Hirshfeld surfaces were used to locate and analyze the deficiencies in various methodologies employed in the determination of the relative energies of five polymorphs of 1,8-dihydroxyanthraquinone. Nine crystallographically independent molecules were characterized by X-ray crystallography and Hirshfeld surfaces were derived from the X-ray structures. The space groups and number of independent molecules (Z′) for each of the polymorphs (1-5) is as follows: (1) P4 1 (or P4 3 ), Z′ ) 1; (2) Pca2 1 , Z′ ) 2; (3) P1 j , Z′ ) 4; (4) P2 1 /n, Z′ ) 1; (5) P4 1 2 1 2 (or P4 3 2 1 2), Z′ ) 0.5. Form 1 is the most thermodynamically stable among the reproducible structures, as established by competitive solubility tests, followed by 2 and then 4. The unrestrained structures of the five polymorphs were computed using the CVFF and COMPASS force fields as well as with the density functional code, SIESTA.

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.