Molecular arrays, diffraction patterns from

The method that cnrrently yields reliable biomacromolecular structure at atomic resolution is X-ray diHraction from a single crystal. A molecular structure solved to atomic resolution means that the position of each atom could be distinguished from those of all other atoms in three-dimensional space without applying additional assumptions concerning the structure of the molecule. X-rays are photons with wavelengths in the range of 1 to lOOOnm. Typical X-rays used in structure determination are K rays of Cu (X. = 15.4nm) and Mo (X = 7.1 nm). X-ray and neutron diffraction patterns can be detected when a wave is scattered by a periodic structure of atoms in an ordered array such as a crystal or a fiber (Blundell and Johnson, 1976 Rousseau, 1998 Woolfson, 1997). 

Figure 4.3 HRTEM image and corresponding diffraction pattern (inset) of zeolite Y-templated ordered microporous carbon.Reprinted with permission from Z.X. Ma, T. Kyotani, Z. Liu, O. Terasaki and A. Tomita, Chem. Mater., Very High Surface Area Microporous Carbon with a Three-Dimensional Nano-Array Structure Synthesis and its Molecular Structure. 13, 4413. Copyright (2001) American Chemical Society...

The a helix conformation of the polypeptide chains is demonstrated by three techniques infrared spectroscopy, circular dichroism and X ray diffraction. Infrared spectra exhibit the two characteristic bands of the a helix the amide I band at 1655 cm and the amide II band at 1545 cm . Circular dichroism spectra exhibit the two negative peaks characteristic of the a helix a broad peak centered at 222 nm and a peak at 209 nm. Low angle X ray patterns provide the parameter D of the hexagonal array of the polypeptide chains from D and the molecular chracteristics of the polypeptide, block (molecular weight m of the monomer unit and specific volume Vb of the polypeptide block) one obtains the length of the projection on the helix axis of the distance between two monomer units h = 2mVg (/3 N D ) with N = Avogadro s number the value found h = 1.50 0.02 A is the characteristic value of the a helix. 

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