ISOMERS AND MULTIPLETS 143 



movement of the boom increases sharply, and thus the continuous mono- 

 molecular layer is formed. By means of electron microscopic examination 

 it has been found that the molecules assume a two-dimensional crystal struc- 

 ture, with many crystallites. Where these meet there is indication of defects 

 or dislocations which could be the precursor of pores in the membrane- 

 see Figure 6-8, (a) and (b). 



All these approaches presume that pores really exist, and ignore Beutner's 

 old (1911) idea that the membrane's lipid layer is a continuous barrier 

 through which ions and molecules penetrate by either chemical reaction or 

 solution in the lipid layer. This idea still has much appeal, especially in 

 view of what is now known about the changes in transport mechanisms 

 through a film across which a large electrical voltage exists. Thus a typical 

 membrane potential of 100 mv across a membrane whose thickness is 100 A, 

 would exert an electrical field of 100,000 v per cm across the membrane, and 

 nobody knows yet what that would do to a continuous lipid layer. Perhaps 

 acidic and basic organic molecules are formed by electrical discharge, simi- 

 lar to the reactions known in organic transformer oils, to give the layer more 

 of an ionic character so that water and ions can more easily dissolve. 



Structure within the living membrane is a treacherous problem for study; 

 but no problem is more intriguing, and none in biophysics more important. 



ISOMERS AND MULTIPLETS 



This section is concerned with (a) the stereoisomerism which is expected to 

 occur in macro-organic molecules as well as in classical organic molecules; 

 and with (b) excited states which one supposes to exist in macromolecules, by 

 analogy with the properties of smaller ones. These subjects have a bearing 

 on the physical structure of the molecules and their chemical reactivity; but 

 the current practical interest is in their relationship to inherited characteris- 

 tics, to disease, and to benign (passive) and malignant (invasive) tumors. 

 Unfortunately this subject is, experimentally, still in its infancy, although 

 the general principles had been discussed at some length by Delbriick and 

 Schroedinger 6 by 1944. Since the principles are fairly straightforward, and 

 the experimental work by contrast very complicated and as yet not too 

 definitive, we outline first the principles, and relate them to a model, or 

 working hypothesis. 



Isomers 



Stereoisomerism — the existence of two or more chemicals with the same 

 composition and differing only in the arrangement of the atoms — has been 

 known in organic chemistry for a hundred years. Such isomers are truly 

 different compounds, having differing physical and chemical properties. 

 The propyl alcohols will illustrate this basic point. Thus normal propyl 



