Behaviour of inorganic and organic cations in the Debye-Hückel layer of DNA.
Inorganic, monovalent cations (Li, Na, K, Rb, Cs), when present in the Debye-Hückel layer of DNA, are found to bind to the negatively charged groups of the helix solely on the basis of their charge/mass ratio. Thus, when an electric field is applied, the free mobility of the DNA is seen to increase from Li- to Cs-equilibrated DNAs, since the latter cation, having a weaker surface charge distribution and a larger physical size (in the non-hydrated state), is more loosely bound to the DNA helix, thus providing less screening of its negative charges. On the contrary, organic amines (Tris and a number of Good's buffers) are found to bind not only via electrostatic interactions, but by additional bonds, notably H-bonds. In particular, Tris can form two H-bonds, with a purine and pyrimidine, respectively, and a third H-bond shared between the -OH groups of two adjacent Tris. Hence, these buffer components may be unwitting participants in reactions carried out in in vitro systems.
Righetti
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University of Verona, Department of Agricultural and Industrial Biotechnologies, Italy. righetti@mailserver.unimi.it
Magnusdottir
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Gelfi
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Perduca
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D001483:Base Sequence; D002412:Cations / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D017931:DNA Primers; D006860:Hydrogen Bonding; D007287:Inorganic Chemicals / Q000737:chemistry; D008958:Models, Molecular; D009930:Organic Chemicals / Q000737:chemistry
D002412:Cations; D017931:DNA Primers; D007287:Inorganic Chemicals; D009930:Organic Chemicals; D004247:DNA