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Crystallography 101

April 21, 2010 Lowell Bradford Blog, News & Articles 0 Comments

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Crystallography is about symmetry in nature. Art can be crystallographic. Humans are crystallographic. Look at a sunflower's pattern and symmetry, it is crystallographic. Crystallography at the atomic and subatomic levels aids scientists to better understand how certain molecular structures are set up and how they interact in order to provide knowledge to create new classes and orders of drugs, for instance. X-ray crystallography gives scientists an accurate method to study those phase structures by amplifying crystal waves and diffracting them so that the atomic model structures can be refined and used for study.

What is X-ray Crystallography?

X-ray crystallography is an experimental technique resulting in a very accurate molecular structure determined by wavelengths scattered by the electron cloud of an atom of similar size. This is called diffraction. Once the electron cloud is diffused and the x-ray diffraction pattern is established, then the resulting electron density is calculated, and crystallographic phase information is collected. A model is then constructed against the refined data of the technique resulting in the molecular structure.

Basic Crystallography Links:

Crystallography: Crystal structure and minerals: amorphous, isometric, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic, triclinic, are discussed and grouped into the 32 classes of symmetry.

Educational Pamphlets: Teaching material providing tutorials on x-ray diffraction, technique, symmetry, and structural crystallography.

Growing Crystals: How to grow suitably sized single crystals for an x-ray diffraction experiment.

Crystal Structure and Crystal System: Symmetry, lattices, systems, classes, and forms are discussed.

Crystalline Gem Structures: The seven crystal structures, forms, mineral classifications, and refractive indices.

Balance: Short lecture on design balance and its types in nature.

Introduction to Crystallography and Mineral Crystal Systems: This nine-part tutorial covers the forms, symmetry, and systems of crystallography.

X-ray Diffraction Basics: Covers the basics of Bragg's Law and diffraction.

The Crystallographer's Creed: This is Dr. Bernhard Rupp's credo to the x-ray machine and its crystallographer.

The Structures of Life: How x-ray crystallography and art are alike.

Advanced Crystallography Links:

Bragg's Law and Diffraction: Bragg's Law reveals how waves uncover atomic crystal structure.

Diffraction Intensity: Addresses the differences in diffraction spot and plane intensities.

Crystallographic Topology: An entire virtual course on topology of crystallographic groups and simple crystal structures.

Fourier Transforms in Crystallography: The basics of Fourier Transforms and superposition in regard to sine-wave stacking of x-rays.

Miller Indices: Atomic plane in crystal lattice symbolic vector representation examples.

Crystallographic Space Group Diagrams and Tables: A complete hypertext book in both high-resolution and medium-resolution diagrams and tables.

The Project: The search for optimal crystallization conditions for myoglobin in horse skeletal muscle.

Solids and Crystal Structure: Crystals and the spatially periodic structure of solids.

The Phase Problem: 2D Fourier Transforms and the phase problem are introduced for crystal models.

Ewald Construction: The simple geometric construction interpreting Laue's results regarding reciprocal lattices.

Why Crystallography?

Rational drug design, and the ensuing development of therapeutic agents and drugs, are results of knowing these accurate molecular structures. X-ray crystallography does not have the size limitations of the spectroscopic NMR method. It answers specific questions regarding global fold structure and the details of atomic bonding. By looking at 2D and 3D renderings of molecular structure, scientists can ascertain how macromolecules interact and with whom they interact, how enzymatic reactions are catalyzed, and the reaction of drugs. By understanding disease at the molecular, or atomic, level, scientists can better develop new drugs to help people.

Once the crystallographer has found his good crystal or crystals, one single diffraction test is all that has to be undertaken. The main problem is growing the right crystal for the experiment. X-ray crystallography appears to agree well with NMR and general x-ray structures. It is able to be more highly refined for greater study. Greater study leads to greater discovery.

Structure/Dimensional Structure Links:

Interactive Structure Factor: This applet-based tutorial teaches about structure factors, phases, and symmetry, as well as the interrelationship between the factors and the electron density map.

Twinning Test: Plug in your data and complete the twinning test.

Macromolecular X-ray Crystallography: This is an overview studies the methodology of studying 3D structure, the principles of x-ray crystallography, fitting, refinement, and validation.

The Secrets of Crystal Growth: Atomic microscopes aid researchers to discover complex growth mechanisms in solution-based 3D crystals.

Crystal Lattice Structures: Pictorial depiction of lattice structures in crystals indexed by space group, prototype, inter-metallic alloy phases, Pearson symbol, and Strukturbericht designation.

3D Crystal Models: Click on the crystal and rotate it to investigate the symmetry properties.

Crystallography and NMR System: Yale's international collaboration to provide a multi-level hierarchical approach in macromolecular structure determination algorithms.

Database/Article Links:

Cambridge Crystallographic Data Centre: The center has archived is 500,000th crystal structure.

Reciprocal Net: The extensive public portal for distributed crystallography.

Macromolecular Crystallographic Information File: The Protein Data Bank represents macromolecular structure data from x-ray diffraction and NMR studies.

Crystal Structure Database: An exhaustive database interfacing with databases from around the world for crystal structures. Search by mineral, author, chemistry, cell parameters, symmetry, or diffraction,

Crystallography Databases: Resource page of crystal structure databases with interactive files.

Applied Crystallography: These are the full text articles of the XIX Conference on Applied Crystallography held in Poland in 2003.

Rontgen Rays: Full text to the "X Rays, an introduction to the study of Röntgen rays."

Crystallography Glossary: Technical glossary of crystallographic terms.

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