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Orientational interactions in low‐concentration DNA solutions
Author(s) -
Marion Christian,
Roux Bernard,
Hanss Maxime
Publication year - 1983
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360221104
Subject(s) - chemistry , rotational diffusion , relaxation (psychology) , molecule , ionic strength , ionic bonding , birefringence , diffusion , macromolecule , chemical physics , analytical chemistry (journal) , thermodynamics , ion , chromatography , physics , optics , organic chemistry , aqueous solution , psychology , social psychology , biochemistry
The rotational relaxation tiem τ 3 of DNA molecules ( M w ≃ 5 × 10 6 ) in solution has been determined by the transient electric birefringence method. The analysis of the birefringence decay makes it possible to study only the higher‐molecular‐weight fraction, the molecules being considered as rigid elongated particles in a short time scale. A marked concentration dependence of the relaxation time has been observed for DNA in low ionic strengths. Above a critical concentration c *, τ 3 increases with the DNA concentration, c . The value of c * increases with the ionic strength. For 10 −3 ionic strength (with NaCl), c * is about 10 μg/mL; then we observe the same strong concentration dependence of rotational relaxation times as recently reported for rodlike M‐13 viruses [Maguire, J. F., McTague, J. P. & Rondelez, F. (1980) Phys. Rev. Lett. 45 , 1891–1894]. These results may be discussed in terms of the Doi‐Edwards theory for rotational relaxation time of rigid macromolecules [Doi, M. (1975) J. Phys. 36 , 607–611; Doi, M. & Edwards, S. F. (1978) J. Chem. Soc. Faraday Trans. 74 , 918–932] and the critical concentration above which the interactions between the molecules begin to appear allows determining the corresponding molecular length. We observe a very good agreement between the DNA lengths obtained from the c * values and by using the infinite dilution value of τ 3 and Broersma's equation. Therefore, only highly diluted solutions can be used if intrinsic molecular properties based on the rotational diffusion of high‐molecular‐weight elongated molecules are studied.