THE STRUCTURE OF MATTER 75 



In between the ionic and covalent bond is the dative bond, in which the 

 electron of atom 1 is partially given over to atom 2, although exchange and 

 overlap still occur. Organic-phosphorus molecules are an important ex- 

 ample (ATP, for instance, the "mobile power supply" in the living system). 

 The oxygens of the phosphate assume a definite negative charge because of 

 dative bonding. 



Of special importance is the w bond, formed by the overlap of two p orbi- 

 tals ("probosci"). It often forms the second bond in the "double bond" of 

 conjugated organic molecules, and restricts the relative rotation of atoms 1 

 and 2 if joined by the it. But the most important property of the it bond is 

 its position, directed parallel to, but not coaxial with, the atom — atom axis 

 (Figure 5 (b)). Although it helps to bind atom 1 to atom 2, it is an ac- 

 cumulation of negative charge outside the volume containing the two atoms. 

 It therefore can form weak bonds (complexes) with positive ends of other 

 molecules in the vicinity; but, most important, it can exchange electrons 

 with other it bonds close by, and hence provide a pathway by which elec- 

 trons can run along a molecule from a point of excess negative charge to a 

 point of deficiency of charge. Hence some organic molecules in tissues are 

 electronic conductors, a fact which only recently has been appreciated with 

 respect to nerve conduction and photosynthesis. (This very important topic 

 is pursued in Chapter 6.) Further, the possibility of different electronic 

 states in molecules, with different types of bonds, has profound ramifications 

 in interactions of the molecule (and the tissue of which it forms a part) with 

 electromagnetic radiations. These very important topics are also discussed 

 in Chapter 6. 



It is obvious that the elementary particles are the building blocks of the 

 living stuff. From the molecular point of view, however, it is not at all clear 

 where the line is to be drawn between the living and nonliving. Usually the 

 attributes of growth and reproduction are used to classify the living. Yet, in 

 a supersaturated solution, copper sulfate crystals will "grow," layer upon 

 layer; and if the temperature is allowed to fluctuate up and down with a 

 frequency of one or two cycles per day, they will "reproduce" themselves, by 

 "seeding," in the form of many crystallites on the walls of the container. In- 

 deed, Teilhard de Chardin, in 1945, proposed that all the elementary par- 

 ticles of matter are living, that they have the potency to do the things which 

 living things can do, but that this potency is, to us, masked behind the 

 gross behavior of large numbers. The gross behavior — statistical behavior — 

 is all that our experimental techniques can today perceive in inanimate na- 

 ture. Our techniques can examine the highlv organized individual man in 

 which ~10 28 particles are organized and controlled from within, although 

 this inner FORCE is not amenable to physical examination as we know it 

 today. From the point of view of elementary particles, the only difference be- 

 tween living and nonliving matter is one of organization. 



