Aggregated DNA in ethanol solution.

J Piskur; A Rupprecht

doi:10.1016/0014-5793(95)01206-t

Home/Archive/PubMed

PubMed · 7498493

Aggregated DNA in ethanol solution.

J Piskur·A Rupprecht

View original source ↗Export metadata ↓

Abstract

A recently developed mechanochemical method has provided a new, efficient tool for studies on the thermal stability and structure of aggregated DNA in ethanol-water solutions. At low ethanol concentrations DNA is fully soluble and is in the B form. However, with increasing ethanol concentration the melting temperature of DNA, Tm, decreases. At a critical ethanol concentration, dependent on the nature and concentration of the counterion, aggregation of the DNA molecules sets in. This is reflected in a marked increase in Tm indicating that the aggregated DNA molecules are thermally more stable than the dissolved ones. However, they are still in the B form. In general, Tm of aggregated DNA also decreases with further increasing ethanol concentration and is dependent on the nature of the counterion, but Tm is not affected by the concentration of the counterion (excess salt) in the ethanol-water solution. When the ethanol concentration reaches the range of 70-80% (v/v), the B-to-A conformational transition occurs in the case of Na-, K- and CsDNA. Above this transition point the A form is more stable than the B form due to the reduced water activity and to increased interhelical interactions. At very high ethanol concentrations, above 85% and dependent on the nature of the counterion, a drastic change in the thermal behaviour is observed. Apparently such a strong interhelical interaction is induced in the aggregated DNA that the DNA is stabilized and cannot adopt a random coil state even at very high temperatures. This stability of DNA in the P form is fully reversed if the ethanol concentration is lowered and the activity of water, thereby, is restored.

Explore related subjects

Cations, Monovalent DNA Ethanol Models, Structural Nucleic Acid Conformation Nucleic Acid Denaturation Solutions Thermodynamics Water Comparative Study Journal Article Review

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

J Piskur, A Rupprecht. 1995-11-20. Aggregated DNA in ethanol solution.. https://doi.org/10.1016/0014-5793(95)01206-t

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2006

Solid-state 23Na NMR study of sodium lariat ether receptors exhibiting cation-pi interactions.

Noncovalent cation-pi interactions are important in a variety of supramolecular and biochemical systems. We present a 23Na solid-state nuclear magnetic resonance (SSNMR) study of two sodium lariat ether complexes, 1 and 2, in which a sodium cation interacts with an indolyl group that models the side chain of tryptophan. Sodium-23 SSNMR spectra of magic-angle spinning (MAS) and stationary powdered samples have been acquired at three magnetic field strengths (9.4, 11.75, 21.1 T) and analyzed to provide key information on the sodium electric field gradient and chemical shift (CS) tensors which are representative of the cation-pi binding environment. Triple-quantum MAS NMR spectra acquired at 21.1 T clearly reveal two crystallographically distinct sites in both 1 and 2. The quadrupolar coupling constants, CQ(23Na), range from 2.92 +/- 0.05 MHz for site A of 1 to 3.33 +/- 0.05 MHz for site B of 2; these values are somewhat larger than those reported previously by Wong et al. (Wong, A.; Whitehead, R. D.; Gan, Z.; Wu, G. J. Phys. Chem. A 2004, 108, 10551) for NaBPh4, but very similar to the values obtained for sodium metallocenes by Willans and Schurko (Willans, M. J.; Schurko, R. W. J. Phys. Chem. B 2003, 107, 5144). We conclude from the 21.1 T data that the spans of the sodium CS tensors are less than 20 ppm for 1 and 2 and that the largest components of the EFG and CS tensors are non-coincident. Quantum chemical calculations of the NMR parameters substantiate the experimental findings and provide additional insight into the dependence of CQ(23Na) on the proximity of the indole ring to Na+. Taken together, this work has provided novel information on the NMR interaction tensors characteristic of a sodium cation interacting with a biologically important arene.

Cations, Monovalent↗

PubMed2006

Study of lithium ion exchange by two synthetic zeolites: Kinetics and equilibrium.

We examined the exchange of univalent cations (Na+ and H+) retained on two commercially available synthetic zeolites with Li+ ions present in aqueous solutions in contact with the solids with a view to preparing effective controlled-release pharmaceutical forms. The studied zeolites were manufactured by Merck and featured channel diameters of 0.5 (Zeolite 5A, Ref. 1.05705.250, designated Z-05 in this work) and 1.0 nm (Zeolite 13X, Ref. 1.05703.250, designated Z-10 here). The XRD technique revealed that Z-05 possesses an LTA structure derived from that of sodalite and Z-10 a faujasite-type structure. Their exchange capacities were found to be 2.72 and 3.54 meq/g. The Z-Na + Li(+) / Z-Li + Na(+) and Z-H + Li(+) / Z-Li + H(+) ion-exchange processes were found to be reversible and their kinetic laws to obey the equation (-dC/dt) = k(a) x C(n) x (1-theta) - (k(d) x theta), with n = 1 for Z-10 and n = 2 for Z-05. Based on the equilibrium results, the overall processes involve one (with Z-05) or two single ion-exchange processes (with Z-10). In both cases, the equations that govern equilibrium are direct results of the kinetic laws. Thus, the first process-the one with only Z-05-involves the retention of Li+ cations at anionic sites on the outer surface of the solid and their access to the larger pores; the second process-which occurs with Z-10 only-involves the retention of lithium(I) cations within the zeolite channels. In both systems, the exchange with Li+ (from the aqueous solution) is easier than that with H+; this is consistent with our kinetic, equilibrium, and thermodynamic results.

Cations, Monovalent↗

PubMed2006

Identification and characterization of conjugated linolenic acid isomers by Ag+-HPLC and NMR.

Interest in the biological activity of conjugated linolenic acids (CLnA) is growing. Technically, previous methods could not fully characterize and identify CLnA isomers. The present study is the first report on application of silver ion impregnated high-performance liquid chromatography (Ag+-HPLC) into separation of CLnA methyl ester (CLnAMe) mixture. Compared with the GC and reversed-phase HPLC techniques, Ag+-HPLC could resolve and separate CLnAMe isomers into three clusters of peaks namely ttt, ctt and ctc geometrical groups. Each positional isomer belonging to the same geometrical group could be further separated by Ag+-HPLC. Quantitative 13C NMR properties of CLnAMe mixture were subsequently studied. Olefinic signals in the CLnAMe mixture were assigned and used to quantify each isomer in combination with Ag+-HPLC. The present study provided a detailed analysis of a complex CLnA mixture and may have an important application in future studies dealing with synthesis, oxidative stability, and bioactivity of individual CLnA isomers.

Cations, Monovalent↗