Energy transfer in the DNA-chloroquine complex

TY - JOUR

T1 - Energy transfer in the DNA-chloroquine complex

AU - Sutherland, J. C.

AU - Sutherland, B. M.

N1 - Funding Information: citing wavelength is absorbed by DNA. For free chloroquine, the p/\] ratio is the same at 280 and 304 nm, indicating that the increased phosphorescence is not due to increased intersystem crossing at shorter wavelengths. GALLEY 6'7 observed enhanced p/\] in the 9-aminoacridine-DNA complex and pointed out that triplet-triplet transfer proceeds through short range interactions. Thus "sensitized phosphorescence" implies close physical proximity of donor and acceptor. Fig. 3 shows that the increase in p/\] is about 50 % for excitation at 280 nm, smaller than that observed for 9-aminoacridine. This does not imply less efficient triplet-triplet transfer, as the relative enhancement of p/\] is inversely proportional to the probability of intersystem crossing (~ise). Fig. 3 shows that the phosphorescent intensity of chloroquine is the same order of magnitude as the fluorescent intensity (i.e. ~Ise ~ 0-5), while the phosphorescence of 9-aminoacridine cannot be detected in the fluorescent spectrum (i.e. ~blse << o.5) 7. Sensitized phosphorescence of chloroquine is favored by the absence of triplet DNA-singlet chloroquine transfer (energetically impossible, see Fig. 2) which would reduce the number of DNA triplets available for triplet-triplet transfer. The value of p// did not change significantly for r's from 0.05 to o.125. We have demonstrated energy transfer from DNA to chloroquine both in solution at room temperature and in a rigid matrix at 77°K. We find that photochemical techniques are useful not only as a probe of DNA-ligand interactions but also as a means of demonstrating energy transfer when emission of the donor and acceptor are difficult to observe. Since triplet-triplet transfer requires physical proximity of donor and acceptor 7, our observation of sensitized phosphorescence at 77°K is compatible with the hypothesis of O'BRIEN et al. s that chloroquine intercalates between adjacent DNA base pairs. We thank F. E. Hahn for his interest and encouragement, David Ginsberg for the use of his Jagger meter, L. Kayzak for his gift of highly purified chloroquine, and W. C. Galley, McGill University, for helpful discussions. Dr. B.M. Sutherland was a postdoctoral fellow of the National Institute of General Medical Sciences, U.S., Public Health Service, Fellowship I-F2-GM-36, 62o-o2.

PY - 1969/10/22

Y1 - 1969/10/22

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U2 - 10.1016/0005-2787(69)90104-X

DO - 10.1016/0005-2787(69)90104-X

M3 - Article

C2 - 4900583

AN - SCOPUS:0014687879

SN - 0005-2787

VL - 190

SP - 545

EP - 548

JO - BBA Section Nucleic Acids And Protein Synthesis

JF - BBA Section Nucleic Acids And Protein Synthesis

IS - 2

ER -