CHEMISTRY AND BIOCHEMISTRY AT LOW 



TEMPERATURES AND DISCRIMINATION OF 



STATES AND REACTIVITIES* 



Simon Freed 



Chemistry Department, Brookhaven National Laboratory, 

 Upton, New York 



Abstract — In order to apply information theory to biochemistry and biology at the molecular 

 level it is advantageous to reduce the number of classifications and specifications involved by 

 reducing the temperature of the system. In this way the number of species and states with 

 their reactivities is reduced. At the same time the chemical noise level falls and in consequence 

 a resolution may be obtained between components whose properties are practically indis- 

 tinguishable at ordinary temperatures. Weakly bonded systems and intermediates become 

 more easily detectable not only because of an increase in their concentration, that is, an increase 

 in their signal, but in addition because the noise level is weaker at the lower temperatuie. 



Illustrations are given from chemistry where reactions in solutions proceed at the tempera- 

 tures approaching that of liquid nitrogen. The information content of irreversible reactions 

 at room temperature may be thought of as being stored in intermediates that participate in 

 reversible reactions at the low temperatures. 



Once the properties of the more stable states have been understood, the way is clear for 

 investigating the system in its thermally active states since allowance can be made for the 

 presence of the former. In this way, an ordering of experimentation according to temperature 

 will bring into activity successive components of the system. 



Examples have been selected mainly from work on the preservation of biological systems 

 at low temperatures which indicate that biochemical and biological processes may likewise 

 be investigated and that the finer discriminations and specificities associated with lower 

 temperatures may be brought to light in these fields also. 



If we wish to measure a physical property, such as electrical conductivity or 

 viscosity, with an instrument which we have no intention of modifying, there 

 is little point in seeking the information content of the instrument. On the 

 other hand, if we wish to employ chemical substances as probes for uncovering 

 structures of enzymes by means of enzyme-substrate reactions, we are at once 

 confronted by the need of the structural and functional information of our 

 probes. In fact we are discussing properties at the molecular level. Pure 

 substances at this level are mixtures composed of molecules in various energy 

 states with their characteristic configurations, motions, and reactivities. The 

 application of information theory to biology at the molecular level requires 

 therefore a great expansion in the number of categories and specifications. 

 It is to reduce this number in a systematic manner and make these categories 

 more precise that I wish to draw upon the relation that has been recognized 

 between information and entropy which asserts that the amount of information 



* Research performed under the auspices of the U.S. Atomic Energy Commission. 



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