Amino acid racemization dating method

The coefficient of t is presumed to be a constant, corresponding to m, and Const. Since the D-form does not exist in the amino acids of proteins in living organisms, the logarithmic term for t = 0 should be zero (ln 1 = 0), which specifies a zero value for Const.

A non-zero constant term may be required to adjust for a slight racemization produced during the laboratory preparation of a sample (Bada and Shou 1980).

L- and D-forms have opposite rotational effects on the vibrational plane of polarized light.

Due to the strong dependency of racemization rates on temperature, water concentration, and alkalinity, uncertainties regarding conditions of preservation can leave amino-acid-based age relationships among even similar fossils open to question.Small amounts of D-amino acids are found in organisms, but most of the amino acids in organisms are constituents of protein molecules, and all amino acids (except glycine which is symmetric and has no D- and L-configuration) in the protein of living organisms are in the L-configuration (Kvenvolden 1975).Both the D- and the L-configurations of amino acids convert to the other over a period of time, either as the result of random thermal energy or through a catalyzed chemical mechanism.The instability of the twenty amino acids which are the building blocks of proteins provides a possible means for determining the ages of fossils.

A preliminary recognition of this possibility appeared in the scientific literature 30 years ago (Abelson 1955).

Four of the amino acids that make up proteins — isoleucine, threonine, hydroxyproline, and hydroxylysine — have two asymmetric carbon atoms which produce four structural possibilities for the same chemical composition.


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