Affinity binding phenomena of DNA onto apatite crystals

The effect of DNA on the crystal growth of hydroxyapatite (HAp) and its morphology was examined. X-ray diffraction patterns of DNA-containing apatites showed typical apatitic features. However, crystal growth was greatly inhibited in the presence of DNA during synthesis; particularly, the crystallinity in the a-axis direction decreased dramatically at low concentrations of DNA. The a- and c-axis dimensions of each precipitate were almost the same, which implies that DNA molecules affect only the crystal surface. CHN analysis clearly showed the presence of these elements, which increased with an increase in DNA concentration in the solution. Scanning electron micrographs of the precipitates formed in the presence of DNA showed typical needle-like crystals, with a decreased crystal size, especially width. Infrared absorption spectroscopy of the DNA-containing apatites showed that the 1630–1700 cm−1 absorption band due to C=C and C=N stretching increased with an increase in DNA concentration during precipitation. The ESCA spectrum of HApDNA1.0 shows N 1s and C 1s peaks that are absent and weak, respectively in HAp. 31P NMR spectroscopy revealed a weak peak at the base of the 31P peak from the PO43− ions in the HAp crystals. This weak 31P peak had a small positive shift from the position found in native DNA which may be due to the phosphate backbone of adsorbed DNA. The apparent solubility of the HAps increased with an increase in DNA concentration. These results suggest that there is an affinity binding between apatite crystal and DNA molecules.