28 



X-RAY DIFFRACTION AND 

 THE STUDY OF FIRROUS 



PROTEINS 



I. FANKUGHEN, associate professor of crystal chemistry, 



POLYTECHNIC INSTITUTE OF BROOKLYN 

 H. MARK, DIRECTOR, POLYMER RESEARCH INSTITUTE, POLYTECHNIC 



INSTITUTE OF BROOKLYN 



rHlS ESSAY will re\ iew some recent studies with x-rays of 

 the structure of proteins and will discuss a few questions 

 which are still unanswered, but which, presumably, may be success- 

 fully attacked with the aid of x-ray or electron diffraction within the 

 not too distant future. 



The general purpose in applying x-rays for the elucidation of the 

 structure of matter is to obtain information about the exact position of 

 atoms or ions inside a crystal or molecule. Such information can be 

 obtained from diffraction patterns because the diameters of atoms like 

 carbon, nitrogen, and oxygen are of the same magnitude as the wave 

 length of x-rays as they are produced in commercial tubes. Both are 

 between one and two angstrom units, one angstrom unit being 10~^ 

 centimeter. The x-rays diffracted from the three-dimensional atomic 

 lattice of a crystal or a large molecule show particularly high intensities 

 in certain preferred directions, from which one can figure out the dis- 

 tances between the various atoms in the sample. 



This line of attack first led to a thorough understanding of the 

 fine structure of most simple inorganic and organic crystals such as 



439 



