ABSTRACT
The 18ID undulator beamline of the Biophysics Collaborative Access Team at the Advanced Photon Source, Argonne, IL, USA, is a high-performance instrument designed for, and dedicated to, the study of partially ordered and disordered biological materials using the techniques of small-angle X-ray scattering, fiber diffraction, and X-ray absorption spectroscopy. The beamline and associated instrumentation are described in detail and examples of the representative experimental results are presented.
Subject(s)
Academies and Institutes , Biopolymers/chemistry , Crystallography, X-Ray/instrumentation , Software , Spectrometry, X-Ray Emission/instrumentation , Synchrotrons/instrumentation , X-Ray Diffraction/instrumentation , Biopolymers/analysis , Crystallography, X-Ray/methods , Equipment Design , Equipment Failure Analysis , Illinois , Molecular Conformation , Research/instrumentation , Spectrometry, X-Ray Emission/methods , User-Computer Interface , X-Ray Diffraction/methodsABSTRACT
X-ray absorption fine-structure spectroscopy is used to study the local environment of the iron site in natural (human) neuromelanin extracted from substantia nigra tissue and in various synthetic neuromelanins. All the materials show Fe centered in a nearest neighbor sixfold (distorted) oxygen octahedron; the Fe-O distances, while slightly different in the natural and synthetic neuromelanin, are both approximately 2.0 A. Appreciable differences arise, however, in the second (and higher) coordination shells. In this case the synthetic melanin has the four planar oxygens bound to carbon rings with Fe-C distances of approximately 2.82 and 4.13 A; the human sample does not show the 2.82 A link but instead indicates a double shell at approximately 3.45 and 3.78 A.