Abstract
Spectrophotometric Studies of the Interaction of Chloroquine with Deoxyribonucleic Acid
Highlights
The presence of an apparent isosbestic point indicated that the spectra of the limiting systems intersect [28] and permitted selection of a single wave length for the study of complex formation
Since the amount of spectral shift increased with the guanine-cytidine content of the polymer, and the hypochromicity associated with ligand binding to pyrimidine residues was relatively small, it appears that t.he differences observed with DNA preparations from different sources represent primarily a greater pert,urbation effect of guanine on the chloroquine spectrum as compared with adenine
Increased ability to interact with DNA. These findings suggest that a positively charged B ring system is the essential factor in permitting significant interaction to occur, since electron-withdrawing substituents on the A ring, which contribute toward an electron deficit of the B ring, enhance the interaction
Summary
The theory and methods presented by Scatchard [19] and Scatchard, Coleman, and Shen [20] for analyzing the interaction of large polymeric molecules with small molecules (ligands) have been employed to characterize the binding process in these. Interaction between bound ligand molecules, or alterations in either electrostatic factors or polymer secondary structure as a result of complex formation, may produce a nonlinear plot If the latter factors can be eliminated as causes of curvature, nonlinearity of F/C versus pi can be assumed to result from differences in the intrinsic affinities of polymer sites, and characterization of binding can be accomplished by the curve-fitting process described by Scatchard, Coleman, and Shen [20].1. Vol 240, No 7 certain of the polymers examined, D2 could not be determined directly since the amount of polymer available was too limited to permit an excess sufficient to ensure virtually complete binding of ligand In these instances, an extrapolation of the reciprocal plot l/(Dl - D) versus l/Tp indicated an approximate value for total shift in the ligand spectrum (Dl - D2) expected at infinitely high polymer concentrations [22]. Accurate determination of complex formation by the spectrophotometric method could be made for only a limited ? range, since at very low 8 values small errors in D result in enormous errors in F (cf. Reference 4), and ligand concentrations sufficient to produce measurable
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