Mechanochemical study of wet‐spun lithium‐DNA fibers

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Abstract
Uniform LiDNA fiber specimens of nearly 20 m length have been prepared with a wet‐spinning method developed by the author. Samples immersed in the spinning bath (80% ethyl alcohol containing 0.4M LiCl) have been subjected to mechanochemical study involving stretching, relaxation, and contraction measurements. A special technique was developed to transfer the sample from the Teflon‐coated cylinder used in spinning to the sample column of the mechanochemical apparatus without stretching or removing the sample from the spinning bath. Force–strain curves of samples consisting of two fiber bundles showed an initial region of low slope followed by a region of high slope and a second region of low slope up to rupture. Some thicker specimens showed an aging effect which abolished the initial low‐slope region and was interpreted as indicative of crystallization. Force–strain curves of two‐bundle samples showed a strong influence of temperature with a complete loss of tensile strength of the LiDNA fibers in the spinning bath at about 55°C. Furthermore, samples at zero strain exhibited a contractile force when subjected to temperatures above about 40°C; the contractile process was pronounced with samples kept above 48°C. On contraction these samples obtained a zero‐force length 20–30% of the original. These data are taken as evidence for a helix‐to‐coil transition occurring in the DNA, the low melting temperature being caused by the chemical influence of the ambient aqueous alcohol–LiCl bath.