Poly-gamma-methyl-L-glutamate

Date:
1952
Reference:
PP/CRI/H/1/7
Catalogue details

Licence: In copyright

Credit: Poly-gamma-methyl-L-glutamate. Source: Wellcome Collection.

    2/24
    POLY-Ö-METHYL-L-G-LUT AMATE. A possible approach to the side chain problem There are two remaining problems (jan.'52) concerning this structure, as far as X-rays are concerned. They are (1) to establish beyond doubt the precise configuration of the helical chain, (2) to find the side chain arrange « This note deals only with the second® It is tacitly assumed that the first problem has been solved* 9 The basic idea is to construct the observed 3-dimensional Patterson? and then to subtract from it the known theoretical Patterson of the main chain» We then carry out a Patterson superposition procedure with what remains» That is, we place identical versions of the Patterson with their centres on each of the known atomic positions (of the main chain atoms) and add them all up® One then hopes that the composite vector density in the space between the chains is similar to the electron- density of the side chains« We first describe the above method, outlining the mathematics, and then add an elaboration to it« If we loosely denote the main-chain by G and the side- chains by S , we may v /rite the observed Patterson, with an obvious symbolism, as c 2 + CS + sc + s 2 . If we subtract the Patterson of the main-chain (C ) there remains CS + SC + s 2 . Now 3 2 will be mainly located near the z axis. If we now place the centre of the Patterson on the atoms of the main- chain in turn, one hopes that vectors from the main-chain to the side-chain atoms will add up, and the rest will average out, so that in between the chains we may get a glimpse of the side-chain arrangement. We now express this process more precisely.