Denaturation experiments on calf-thymus DNA/polycation complexes in aqueous/organic solvent mixtures
Autor(en): | Schindler, T Nordmeier, E |
Stichwörter: | COIL TRANSITION; CONDENSATION; degree of DNA/polycation complexation; DNA; DNA-denaturation temperature; DOUBLE-HELIX; polycation type; Polymer Science; POLYNUCLEOTIDES; STABILITY | Erscheinungsdatum: | 1999 | Herausgeber: | ELSEVIER SCI LTD | Enthalten in: | POLYMER | Band: | 40 | Ausgabe: | 25 | Startseite: | 7019 | Seitenende: | 7027 | Zusammenfassung: | Polyelectrolyte complexes of calf-thymus DNA and polycations, such as PDADMAC, IONENE, and P4VP were formed and analysed with respect to their thermodynamical stability. The UV-VIS spectrographic melting curves yield two denaturation temperatures, T-m,T-1 and T-m,T-2. This is explained as follows: DNA molecules contain two kinds of repeat unit sequences. There are sequences that are not complexed, they denature at T-m,T-1; the other DNA repeat units are complexed with polycation repeat units, they denature at T-m,T-2 Thereby, T-m,T-2 is much larger than T-m,T-1. That is, polycation binding stabilises calf-thymus DNA. Surprisingly, the absolute value of T-m,T-1 depends neither on the degree of complexation nor on the polycation type. T-m,T-1 agrees quite well with the denaturation temperature of the pure, uncomplexed DNA. Also T-m,T-2 does depend not on the degree of polycation complexation, but on the polycation type. One observes T-m,T-2(PDADMAC)> T-m,T-2(P4VP) > T-m,T-2(IONENE). The probable reason for this series is the polycation molar mass. T-m,T-2 increases slightly as M-w is increased. While T-m,T-1 depends on the concentration of the added NaCl-salt, T-m,T-2 does not. This is explained using the fact that the complexed DNA repeat units are electrically neutral, so that there are no salt/charge interactions. Measurements in aqueous/organic solvent mixtures show that both T-m,T-1 as well T-m,T-2 decrease continually as the content of the organic solvent is increased. Very marked is this effect for water/N-methylformamide, Al w(NMF) approximate to 40%, T-m,T-1 and T-m,T-2 are nearly half as large as in pure water. (C) 1999 Elsevier Science Ltd. All rights reserved. |
ISSN: | 00323861 | DOI: | 10.1016/S0032-3861(99)00057-9 |
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