EXAFS Studies of Cobalt(II) Complexes with Amino Acids

摘要

X-ray K-absorption edges along with their extended X-ray absorption fine structure (EXAFS) have been recorded for Co(II) complexes with amino acids using a laboratory XAFS spectrometer. The samples studied are biologically important because amino acids are very small bio molecules and are the principal building blocks of proteins and enzymes. The samples studied include cobalt glycinate, cobalt alanate, cobalt valinate and cobalt glutamate. Using the experimentally observed X-ray absorption chemical shifts, effective nuclear charge (ENC) and percentage covalency have been estimated and a relative order of covalency amongst the studied complexes established which follows the sequence: alanate > glutamate > glycinate > valinate. Both X-ray absorption near edge structure (XANES) and EXAFS have been utilized to obtain the average near neighbour distances in the samples. Further, the total phase shifts 1 and phase parameters 1 i.e., back scattering phase shifts for these samples have been estimated. The values of 1 support the view that the environment around the central metal ion cobalt is similar in these complexes. The appearance of white lines (WL) at the K-absorption edges in these samples is discussed.