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Posted by / 11-Oct-2020 10:35

Dating antarctic ice cores

In other work, the rate of racemization of aspartic acid, instead of isoleucine, was used.

The rate of racemization is highly temperature dependent.

The extent of conversion of L-isoleucine to D-alloisoleucine in core sediment samples from various depths was then determined and conclusions based on the above rates were used to estimate the ages of the sediments from various core depths. Fragments of bone recovered from the Arizona desert and believed to be 2-3 years old were sealed in glass ampoules and heated at various temperatures.

The fragments were then hydrolyzed in 6M hydrochloric acid and the extent of racemization of L-isoleucine to D-alloisoleucine was determined.

The two forms are known as L-amino acids and D-amino acids, the L and D designating the direction in which solutions of these amino acids rotate plane-polarized light.

They are mirror-images of each other, and one cannot be superimposed on the other, just as is true of left and right hands.

Complicating things somewhat is the fact that some amino acids have two asymmetric carbon atoms and can exist in four different forms, known as diastereoisomers.

Racemization is complete when equal amounts of the L- and D-forms are obtained.When there is only a single asymmetric carbon atom, these two different forms are known as optical isomers.Chemically, there is very little difference between them, but biologically, there is as much difference as night and day.All amino acids in proteins (except glycine) are L-amino acids.These amino acids spontaneously tend to slowly change to the D-form.

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At a widely publicized news conference in August of 1972, Dr.