Examples of Organometalcarbonyl Bioprobe Structures

The information available so far clearly demonstrates that arenes complexed by Cr(CO)3 are suitable candidates for probes for 7t-stacking effects. Solvated and 7t-stacked structures show different IR band positions, and progressive interconversion of the two forms occurs as the tendency to 7t-stack is increased. This behaviour is more similar to the effects of interconversion of associated and dissociated forms in pH measurements (Section 7.5.2 and Fig. 7.9a) or empty and occupied crowns in metal ion measurement (Section 7.5.3), than to the shifting ofbands that occurs when different solvents are mixed (Section 7.5.1 and Fig. 7.7a). 

This in itself is evidence for a more specific type of interaction in cases where arenes can approach the uncomplexed face of the (arene)Cr(CO)3 complex. Furthermore, direct evidence for face-to-face interactions between free and complexed arenes is available from studies of cyclophane complexes, as in the solid state, the separation between the arene rings of cyclophanes has been shown by X-ray crystallography to decrease when one of the rings is complexed to Cr(CO)3 [54]. 

Two distinct approaches have been used for the development of organometallic bioprobe structures. The organometallic component can be attached to a small molecule that interacts with a biological receptor system (Fig. 7.13), or directly to a biological macromolecular structure. 

Nucleotide bases (Fig. 7.16) have been derivatized by use of electrophilic organoiron complexes. The carbonyliron adducts 37 and 38 are typical examples [98]. A recent development in this field has led to the synthesis [99] of an extensive set of stmctures, including 39 which more closely resembles a nucleoside. The thymidine derivative 40 is an inhibitor of human thymidine kinase [100]. In the case of 41, the carbonylmetal component is attached at the heterocyclic base [101]. The carbonylmetal component can also be attached to dinucleotides by coordination at a phosphite, placed (as in 42) where the phosphate link would normally join the ribose rings [102]. The attachment of carbonylmetal labels to oligonucleotides for analysis by FTIR has also been described. The succini-midyl-based delivery strategy is the same as that used with proteins, as a 

H2N(CH2)j0P(0)20 linker was added to a universal primer oligonucleotide sequence (GTTTTCCCAGTCACGAC) [103], This was employed with Bacillus stearotherophilus (BST) DNA polymerase. The carbonylchromium complex 43 has been prepared in a study of carbonyhnetal labels on PNA (peptide nucleic acid) monomers [104], 

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