Superconductivity
In a normal material, electrons moving through the lattice encounter resistance from defects, impurities, and lattice vibrations. A superconductor is a material in which electrons flow without experiencing any resistance. A mathematical theory has been developed (BCS theory) that explains superconductivity on the basis of pairing of some of the free electrons to form Cooper pairs (50).
Superconductivity was generally thought to be a phenomenon associated only with metals at temperatures below about 20°K. Beginning in the mid-1960's, however, theoreticians predicted the existence of room temperature superconductivity in organic materials, including long-chain polymers (51, 52), and sandwiches consisting of conducting films and an insulating layer (53, 54). In the early 1970's experimental evidence for superconductivity in organic solids was reported. Halpern and Wolf found that two of the cholates, a family of bile salts, exhibited superconductive behavior in microdomains inside the salts (whose macroscopic properties were those of ordinary insulators) (55). The observed transition temperatures were 30-60° K, but, in subsequent studies of cholates, transition temperatures as high as 277°K (sodium cholanate) were found (56, 57). Ahmed et al. reported superconduction in a 0.1% lysozyme solution at 303°K (58).
The temperature dependence of the single-electron tunneling current between adjacent superconductive microdomains in a material can be shown to be:
where a is a constant, T is absolute temperature, k is Boltzmann's constant, Eo is one-half the binding energy of a Cooper pair at 0° K, and Tc is the temperature below which the material is a superconductor. If one assumes that a biological process is rate-limited by single-electron superconductive tunneling, then i can be identified with the rate of the process, and E with its activation energy. Under this assumption, E-determined from the Arrhenius plot of the data-should satisfy equation (2). Cope found six sets of biological data that showed the behavior expected for rate limitation by single-electron superconductive tunneling (59) (see table 4.1).
Table 4.I. SUPERCONDUCTION PARAMETERS FOR BIOLOGICAL PROCESSES
Thus, his analysis suggests both the existence of superconductive microdomains in biological tissue, and a physiological role for superconductivity. Cope has obtained further evidence that superconductivity occurs in biological tissue from an analysis of the magnetization characteristics of RNA, melanin, and lysozyme (60).