Studies on the interaction between sodium lauryl sulfate and hydroxyapatite using Fourier transformed infrared...

The interaction between sodium lauryl sulfate (SLS) and hydroxyapatite (HA) was studied by using Fourier transformed infrared spectroscopy. The adsorption isotherms to HA and enamel were also established. The results obtained by infrared spectroscopy demonstrated that there was no direct evidence of hydrocarbon interactions between the two compounds since the (CH2)n signal remained unchanged. In contrast reacted mixtures of SLS and HA showed a disappearance of absorption bands between 1220 and 1260 due to stretching of S = 0 bonds. This indicates that the sulfate groups interacted with the HA-crystal surface. Treatment of HA-powder and dental enamel with different concentrations of 35S-labelled SLS showed saturation patterns with a maximum of 3.5 micrograms/mg HA and a maximum of 0.68 microgram/mm2 enamel. This study showed that SLS binds to HA through the sulphate groups and that the binding is most likely electrostatic in nature; the interaction mediated between SLS molecules and calcium ions distributed in the hydration layer of the enamel.