Capillary electrophoresis as a probe of enantiospecific interactions between photoactive transition metal complexes and DNA

Abstract

Recently, we have demonstrated the capacity to separate chiral transition metal (TM) complexes of the type [M(diimine)(3)](n+) using CE buffers containing chiral tartrate salts. In separate work, several chromium(III)-tris-diimine complexes in particular have been shown to bind enantioselectively with calf-thymus (CT) DNA, and a qualitative assessment of the relative strength and enantiospecificity of this interaction is of significant interest in the characterization of these complexes as potential DNA photocleavage agents. Here, we describe two convenient approaches to investigate such binding behavior using chiral CE. For complexes with lower DNA affinities exhibiting primarily surface binding, DNA itself is used as the chiral resolving agent in the electrophoretic buffer. In this approach, resolution of the TM complexes into their Lambda and Delta isomers is achieved with the isomer eluting later exhibiting superior binding affinity toward DNA. For more strongly bound TM complexes containing ligands known to intercalate with DNA, the [Cr(diimine)(3)](3+) complexes are preincubated with oligonucleotide and subsequently enantiomerically resolved in a dibenzoyl-L-tartrate buffer system that facilitates analysis of the unbound TM species only. Differences in isomer binding affinity are distinguished by the relative peak areas of the Lambda- and Delta-isomers, and relative binding strengths of different complexes can be inferred from comparison of the total amount of unbound complex at equivalent DNA/TM ratios.

Bioanalytical interaction studies executed by preincubation affinity capillary electrophoresis

“…Upon separation from the protein, verapamil migrated into the CD containing solution where complexation led to separation of the individual enantiomers [72]. Quite a similar setup was used by Schaeper et al [130] demonstrating stereoselective binding of transition metal complexes to DNA using pre-eq CZE.…”

Capillary electrophoresis of inorganic ions: An update

“…The most recent developments in the area include separation and peak characterization of platinum metal adducts with DNA nucleotides using a coupled CE-ESI-MS approach [120,121] or complementary off-line ESI-MS measurements [261], investigations of the kinetics of binding reactions for the approved and potential tumor-inhibiting platinum(II) complexes toward important biomolecules [120,121,261], including human serum albumin binding assessed by CE-ICP-MS [109], and of effects of other physiologically relevant molecules, such as the sulfur-containing amino acids, on the adduct formation behavior [120]. In a related study, the feasibility of chiral CE for investigating the binding between transition metal complexes and DNA and in particular, for a qualitative assessment of enantiospecificity of such interactions was shown [262].…”

Recent Developments in Affinity Capillary Electrophoresis: A Review

“…Schaeper et al used DNA to separate transition metal complexes of the type [M(diimine) 3 ] n+ into their isomers [60]. Equilibrium dialysis was used to verify the results obtained by CE.…”