Photographic Preparation of Masks of Large Molecules for the Lipson Diffractometer

Abstract

THE optical diffractometer¹ developed by Lipson and others is being used in this laboratory for work on the structure of deoxyribose nucleic acid. This instrument has already proved its value, in work on structures of smaller molecules, as a rapid means of obtaining diffraction patterns due to trial structures, and it should clearly lend itself to application in the field of macromolecular structure in cases where enough is already known of the chemistry to enable trial structures to be produced. In the usual form, a projection of the trial structure is represented by holes punched in an opaque mask, and the Fourier transform of this mask is obtained optically. A difficulty arises, however, in the application to large molecules, in that there is a minimum size of hole (about 0.5 mm. diameter) that can be punched in the mask. As a consequence, a large molecule can only be represented by covering a large area of the mask with holes. This gives a diffraction pattern on a very small scale, and it is found difficult to obtain the pattern without some distortion due to slight imperfections in the lens system.