Isoleucine racemization dates

Table V. Isoleucine Racemization Dates on Total Hydrolysates of Fossil Chione from Interglacial Marine Terraces in San Diego County (20)...

The alleu/iso ratios for these latter two terrace exposures are close to the nonlinear portion of the kinetics plot (30). Therefore, it may not be possible to date absolutely older terraces in the San Diego area by the extent of isoleucine racemization in total hydrolysates of Chione. Because of the slower kinetics of isoleucine racemization in the protein... 

Bada, J. L. (1972), Dating of bones using the racemization of isoleucine, Earth Planet. Sci. Lett. (July). 

J.L. Bada, The Dating of Fossil Bones using the Racemization of Isoleucine, Earth and Planetary Science Letters, 15, 223 231 (1972). 

A novel technique for dating archaeological samples called amino acid racemiza-tion (AAR) is based on the stereochemistry of amino acids. Over time, the configuration at the a-carbon atom of a protein s amino acids is lost in a reaction that follows first-order kinetics. When the a carbon is the only chirality center, this process corresponds to racemization. For an amino acid with two chirality centers, changing the configuration of the a carbon from L to D gives a diastereomer. In the case of isoleucine, for example, the diastereomer is an amino acid not normally present in proteins, called alloisoleucine. 

Racemization, the interconversion of amino acid enantiomers, occurs slowly in biological and geological systems. The rate increases with extreme pH values, high temperature, and high-ionic strength. Rates also vary between amino acids At 25°C, the racemization half-life of serine is about 400 yr, while that of isoleucine is 40,000 yr. Enantiomer analysis is used to confirm bioactivity of synthetic peptides and for geological dating. ... 

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