NMR determination of the hetero-association of phenanthridines with daunomycin and their competitive binding to a DNA oligomer.
ABSTRACT 500 MHz (1)H NMR spectroscopy has been used to determine thermodynamic and structural information on the hetero-association of daunomycin (DAU) with the phenanthridine mutagenic dyes ethidium bromide (EB) and propidium iodide (PI). The NMR complexation data have been analysed by a statistical-thermodynamic model which takes into account indefinite association for both the self-association of the drugs and their hetero-association. The results have been used to estimate the effect of the side chains of the phenanthridines on the competitive binding between DAU and the mutagens with DNA. Knowledge of the equilibrium constants for self-association of the phenanthridines and DAU, their hetero-association and their complexation with a DNA fragment, the deoxytetranucleotide 5'-d(TpGpCpA), enabled the relative content of each of the EB-DAU, PI-DAU, EB-DAU-d(TGCA) and PI-DAU-d(TGCA) complexes to be calculated as a function of drug concentration in mixed solutions. The results provide some insight into the molecular basis of the action of combinations of biologically-active molecules. When intercalating drugs are used in combination, it is found that the decrease in binding of drug or mutagen with DNA is due both to formation of drug-mutagen hetero-association complexes in the mixed solution and to competition for the binding sites by the aromatic molecules; the relative importance of each process depends on the molecular properties of the drug or mutagen molecules being considered. Thus, the longer branched side chain of PI and the electrostatic contribution of the extra positive charge of the molecule compared with the ethyl group of EB results in lower affinity for self-association of PI molecules and their hetero-association with DAU, but increases the degree of binding of PI with DNA.
SourceAvailable from: Maxim P Evstigneev[Show abstract] [Hide abstract]
ABSTRACT: Knowledge of the physical chemistry of small molecules complexation (the hetero-association) in aqueous solution is increasingly important in view of the rapidly emerging branch of supramolecular chemistry dealing with the formation of heterogeneous polymeric structures having specific functional roles. In this paper, the 50-year history of scientific studies of hetero-association of heterocyclic aromatic molecules in aqueous solution has been reviewed. Some important correlations of structural and thermodynamic parameters of complexation have been reported based on large data-set of hetero-association parameters accumulated to date. The fundamental problem of ‘energetic composition’ of π-stacking is extensively discussed. The review has shown that there are some gaps in our understanding of hetero-association, which provides a challenge for further studies in this area.International Reviews in Physical Chemistry 04/2014; 33(2). DOI:10.1080/0144235X.2014.926151 · 4.92 Impact Factor
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ABSTRACT: The method of second harmonic generation (SHG) was applied to the study of drug-DNA interactions at colloidal particle interfaces in order to selectively and quantitatively probe bio-molecular reactions without the need for chemical labels or invasive detection methods. In particular, the binding of the anti-cancer drug daunomycin to a recognition triplet sequence in a 33-mer of double stranded DNA bound to colloidal silica beads was studied as a model system using the SHG method. Probing bio-molecule coated colloids is expected to yield larger SH signals and provides experimental flexibility as compared to experiments performed at planar interfaces. The change in SHG intensity as daunomycin was added to the microparticle solution was fit to a Langmuir binding model, which yielded an equilibrium constant of 2.3 (± 0.7) × 105 M-1; the corresponding Gibbs free energy change at 20 °C is -7.2 ± 0.2 kcal/mol. Control experiments established that daunomycin preferentially binds to DNA at the recognition sequence. The equilibrium was found to be unaffected by the presence of free DNA in solution, and hyper-Rayleigh scattering from bulk molecules did not change with increasing daunomycin concentration. The objective of the research presented here was to compare the SHG measured results to findings using other methods. It was found that the extracted equilibrium constants are in agreement with the range of reported values found in the literature, illustrating the utility of this label-free technique to selectively and quantitatively study bio-molecular interactions.The Journal of Physical Chemistry B 02/2013; 117(49). DOI:10.1021/jp311634a · 3.38 Impact Factor
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ABSTRACT: The structure–activity relations of a series of synthetic phenoxazone drugs with aminoalkyl side chains of variable length and different terminal groups were investigated by examining their biological activity and DNA complexation affinity. Biological activity was determined from their ability to induce apoptosis and cell cycle perturbations (activation of cell cycle checkpoints) using the human malignant MOLT-3 cell line. The thermodynamic parameters of drug–DNA complexation were determined by differential scanning calorimetry. By comparing the activities of compounds with different terminal groups (amino, dimethylamino and diethylamino), we found that the existence of a terminal dimethylamino group in the alkylamino side chain is an important factor for anti-tumour activity. Minor modifications in the dimethylaminoalkyl side chain (e.g. elongation by one methylene group) led to notable changes in both the anti-tumour activity and DNA-binding properties of the drug, providing unambiguous evidence of a marked structure–activity relation.European Journal of Biochemistry 01/2003; 270(20). DOI:10.1046/j.1432-1033.2003.03817.x · 3.58 Impact Factor