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An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.

Eighty specimens of cellulosic materials were analyzed over a period of several years to study the diffraction characteristics resulting from polymorphism, crystallinity, and chemical substitution. The aim of the study was to produce and verify the quality of reference data useful for the diffraction analyses of cellulosic materials. These reference data can be used for material identification, polymorphism, and crystallinity measurements. Overall 13 new references have been characterized for publication in the Powder Diffraction File (PDF) and several others are in the process of publication.

An experimental X-ray powder diffraction pattern was produced and analyzed for imipenem monohydrate, an antimicrobial pharmaceutical agent. Although there are no experimental powder patterns in the ICDD PDF-4/Organics Database, there is one powder pattern calculated with single-crystal X-ray diffraction data from the Cambridge Structural Database. Here, we report the refined experimental powder diffraction data for imipenem monohydrate. These data for imipenem monohydrate are consistent with an orthorhombic crystal system having reduced unit-cell parameters of a = 8.2534(3) Å, b = 11.1293(4) Å, and c = 15.4609(6) Å. The resulting unit-cell volume, 1420.15(15) Å 3 , indicates four formula units per unit cell. Observed peaks are consistent with the P 2 1 2 1 2 1 space group.

By using data mining techniques specifically focused on the process of phase identification, trace and minor phases can be identified and then quantitatively analyzed. The data mining attempts to intelligently mimic the thought process of experts in materials and analytical methods to combine several “data clues” for a successful identification process. The clues can come from the diffraction experiment, but also physical properties, chemical composition, other analytical data, visual observations, or the users knowledge of the specimen and specimen preparation methods used. The method described is generic and is particularly useful in identification and quantitation of trace and minor phases where the diffraction data by itself may not be statistically sufficient but combined with other observations can be definitive.

Since the creation of the Joint Committee on Powder Diffraction Standards (JCPDS) over sixty years ago, the Powder Diffraction File (PDF) has been the key source of standard powder diffraction data for identification and analysis of materials of all types, from natural minerals and high-tech ceramics to metals and alloys and pharmaceuticals. Although this editorially reviewed database has been the mainstay for diffraction pattern reference for the x-ray powder diffraction community, recent developments provide information and tools for electron diffraction. In recent years, the International Centre for Diffraction Data (ICDD, formerly JCPDS) has transformed the flat-file format of the PDF to a more flexible relational database (RDB) format. The PDF has been greatly expanded to include calculated patterns from multiple collaborating databases, including the Inorganic Crystal Structure Database (FIZ Karlsruhe, Germany), the Linus Pauling File (MPDS, Vitznau, Switzerland), and the Cambridge Structural Database (CCDC, Cambridge, United Kingdom). A significant portion of its entries include atomic coordinates and a specific database dedicated to organic phases exists. All new entries for the ICDD databases undergo over 100 quality checks before inclusion, and a quality mark is assigned for each entry that passes.

The ICDD sponsored a round robin on the quantitative Rietveld phase analysis of pharmaceuticals. 11 participating laboratories from the pharmaceutical community submitted both raw data and processed quantitative results. The purpose of the round robin was to evaluate current practices in laboratories, so procedures and methods were not specified, but they were recorded. Cluster analysis tools were applied to all the data sets and their use helped identify the root causes of several types of errors in specimen preparation, data treatment, and Rietveld analysis. The authors considered this round robin to be difficult. Sample homogeneity was an issue and molecular orientation was observed in many data sets. Each material studied has structural polymorphs so the selection of starting parameters and their refinement was nontrivial. Similar to prior round robins on inorganic materials and minerals, this round robin identified operator errors as the major contributor to poor results. Four laboratories achieved excellent results on all phases in all three samples, with accuracy within relative errors of 5% to 10%.

Sessionsdistribution of conformational states represented in the PDB.A systematic review of multiple deposits shows that a single protein is rarely represented by a single structural conformer.This result sheds light on the first link and demands the reformulation of the proteinfolding problem.A vast majority of proteins shows significant number of distinct conformational states with, sometimes large, structural divergence (up to ~24Å).The results suggest that every single protein evolved according to its own optimization principles combining different proportions of rigid (solid-like) and mobile (liquid-like) structural elements.The results suggest further that the optimization process that produced the particular combination of those elements is intricately connected with the function of individual proteins.Therefore, the structural description of the protein, besides the folding class (the architecture represented by the SCOP database), should include the natural structural divergence (width of the distribution) as two main attributes.Additionally, our analysis suggested the principles of functional evolution by use of the Dual Personality sequences (sequences with incomplete representation in the atom records that have distinctive sequence features from regularly folded and intrinsically disordered fragments).

PDF-4/Organics 2008 is ICDDs collection of standard reference X-ray powder diffraction (XRPD) patterns for organic compounds. It includes 29,653 experimental patterns and 311,887 patterns derived from single crystal data. Most of the derived patterns are based on data from the Cambridge Structural Database (CSD) through an agreement between ICDD and CCDC (Cambridge Crystallographic Data Centre). This database contains XRPD patterns for more than half of the USP (United States Pharmacopeia) APIs (active pharmaceutical ingredients) and their polymorphs. Additionally, it contains a large number of patterns for inorganic and organic excipients typically found in pharmaceutical formulation. Since the solid state of a pharmaceutical substance can affect its pharmacological action, the polymorph study is a must for any API, which can exist in more than one solid state. PDF- 4/Organics 2008 contains many substances with polymorphs and has many physical and chemical properties associated with polymorphism. These include habit, space group, cell parameters, cell volume, crystal system, density, and melting point. There is also standardized cell data as well as author-reported raw data in the database. The standardization assures data uniformity. It provides not only the swift and easy means for data comparison, but also the accuracy of data representation. The population distribution for these properties and their applications were studied, compared, and will be presented. Many phase identification processes have been widely researched and reported. These processes generally utilize techniques involving data reduction, peak finding, modeling, and refinement. Illustrations of this traditional process, for pharmaceutical materials, using PDF-4/Organics 2008 for the pattern matching between experimental data and reference patterns will be given.

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