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Quantitative IR Analysis in the Picomole Range of Organometallic-Labeled Biomolecules in KBr Disks

Volume 43, Number 8 (Dec. 1989) Page 1497-1498

Butler, Ian S.; Vessières, Anne; Salmain, Michèle; Brossier, Pierre; Jaouen, Gérard


Quantitative IR studies of materials dispersed in KBr disks are often unreliable because of variable sample homogeneity due to incomplete mechanical mixing. The inherent difficulties in this type of measurement are exacerbated when one is examining the extremely small amounts of material encountered with biological samples. We report here a simple, quantitative KBr-disk procedure for the IR detection of biologically important molecules at physiological levels (picomoles). This analytical technique is based on one's labeling the biomolecules with transition metal carbonyl fragments, such as Cr(CO)3, Mn(CO)3, and Co2(CO)6, and then taking advantage of the rapid multi-scanning capability of an FTIR spectrometer to detect the CO stretching vibrations of the organometallic labels in BKr disks of the solids from the subsequent biochemical precipitations. Metal carbonyl complexes containing terminal CO groups were selected as the IR markers because the v(CO) modes exhibit intense absorptions in the 2150-1900 cm−1 range, a region which is normally devoid of peaks associated with the vibrational modes of biomolecules, such as v(OH), v(NH), v(CH), v(C=O), v(C=C), and v(C-C). This non-radioisotopic procedure has already been successfully applied in estradiol receptor and immunoassay.