Amino racemization dating
In this article we shall discuss the principles behind amino acid dating (also known as racemization dating); we shall discuss how it ought to work, and why it often doesn't.
An object is said to have chirality if it is not possible to make it into a mirror-image of itself by turning it round.
Racemization occurs when one pure form of an enantiomer is converted into equal proportion of both enantiomers, forming a racemate.
When there are both equal numbers of dextrorotating and levorotating molecules, the net optical rotation of a racemate is zero.
But after its death, the amino acids can spontaneously change their chirality, flipping from being left-handed to right-handed, and indeed back again.
The result of this process is that eventually the amino acids will collectively become racemic: each particular amino acid will have one chirality or another, but after a sufficient amount of time, collectively the amino acids won't favor one enantiomer over another. We should note that although the underlying basis for this process is random, and that in principle the amino acids could by some statistical fluctuation become less racemic and more chiral, the laws of statistics ensure that in practice if we are looking at a large enough sample of amino acids, the chances are astronomically remote that such a thing will occur.
Crystallization of a racemate can result in separate ( ) and (−) forms, or a single racemic compound.
Establishing an accurate and reliable chronology for these deposits has fundamental implications for understanding the patterns of human evolution and dispersal.When an organism dies, control over the configuration of the amino acids ceases, and the ratio of D to L moves from a value near 0 towards an equilibrium value near 1, a process called racemization.Thus, measuring the ratio of D to L in a sample enables one to estimate how long ago the specimen died.The rate at which racemization proceeds depends on the type of amino acid and on the average temperature, humidity, acidity (p H), and other characteristics of the enclosing matrix.Also, D/L concentration thresholds appear to occur as sudden decreases in the rate of racemization.