Analysis of Oligonucleotide DNA Binding and Sedimentation Properties of Montmorillonite Clay Using Ultraviolet Light Spectroscopy

Abstract

Smectite clays such as montmorillonite form complexes with a variety of biomolecules, including the nucleic acids DNA and RNA. Most previous studies of DNA adsorption onto clay have relied upon spectrophotometric analysis after separation of free nucleic acids from bound complexes by centrifugation. In the current work we demonstrate that such studies produce a consistent error due to (a) incomplete sedimentation of montmorillonite and (b) strong absorbance of the remaining clay at 260 nm. Clay sedimentation efficiency was strongly dependent upon cation concentration (Na + or Mg 2+ ) and on the level of dispersion of the original suspension. An improved clay:DNA adsorption assay was developed and utilized to assess the impact of metal counterions on binding of singlestranded DNA to montmorillonite. X-ray diffraction demonstrated, for the first time, formation of intercalated structures consistent with orientation of the DNA strands parallel to the clay surface. Observed gallery spacings were found to closely match values calculated utilizing atomistic modeling techniques.

Impact of size, secondary structure, and counterions on the binding of small ribonucleic acids to layered double hydroxide nanoparticles

“…33 In order to investigate the adsorption of nucleic acids to HT we employed centrifugation binding assays. 8 By mixing the nucleic acids with HT in water and spinning the samples for 5 min at 21 000 Â g, we were able to quantitate the amount of the free nucleic acids versus those that adsorbed to the sedimented HT by measuring the A 260 of the supernatant after the spin. In the first set of experiments, DNA and RNA 25mers were mixed with increasing amounts of HT.…”

“…[6][7][8][9][10] Two commonly studied nanoclays, hydrotalcite (HT) and montmorillonite (MMT), have high anion (100-500 mEq/ 100 g) or cation (80-150 mEq/100 g) exchange capacities, respectively. [8][9][10][11] This allows them to adsorb large amounts of biomolecules. MMT is classified as a cationic nanoclay due to its high exchange capacity of cations, while HT is an anionic clay capable of exchanging anions.…”

“…Recently, both nanoclays have shown great promise for the delivery of biomolecules and drugs into mammalian cells. 4,[6][7][8][9][10]12 HT is a member of the layered double hydroxide family and has been found to be particularly promising for gene delivery and controlled drug/deoxyribose nucleic acid (DNA) release systems. 7,[13][14][15][16][17] Similar to MMT, HT is commonly used in a variety of different applications, such as water treatment, flame-retardants, sorbents, cosmetics, and as enteric delivery vehicles for antacids.…”

“…7,[13][14][15][16][17] Similar to MMT, HT is commonly used in a variety of different applications, such as water treatment, flame-retardants, sorbents, cosmetics, and as enteric delivery vehicles for antacids. 5,8,16 HT can be described with À ions and every octahedral subunit pair shares edges, leading the two-dimensional layer to expand infinitely. [13][14][15][16] Isomorphic substitution of Mg 2þ ions by Al 3þ ions gives these layers a net positive charge.…”

Organic phosphorus in the aquatic environment

“…There is a large body of work suggesting that DNA can attach to clays. [45] An X-ray diffraction and molecular mechanics study has shown that DNA can form intercalated structures in layered (swelling) clays -the DNA resides between clay layers and is bound to the clay structure through phosphate bonds to claybound interlayer cations (e.g. Ca 2þ or Mg 2þ ).…”