Effect of amino acids on aggregation behaviors of sodium deoxycholate at air/water surface: surface tension and oscillating bubble studies.

The aggregation behaviors of sodium deoxycholate (NaDC) at the air/water surface were investigated via surface tension and oscillating bubble measurements in the absence and presence of three alkaline amino acids, namely, l-Lysine (l-Lys), l-Arginine (l-Arg), and l-Histidine (l-His). The results of surface tension measurements show that NaDC has a lower ability to reduce the surface tension of water, because NaDC molecules orient at the surface in an oblique direction and tend to aggregate together, which is approved by molecular dynamics (MD) simulation. l-Lys is the most efficient of the three amino acids in reducing the critical aggregation concentration (cac) of NaDC in aqueous solution. The influence of amino acids on the dilational rheological properties of NaDC was studied using the drop shape analysis method in the frequency range from 0.02 to 0.5 Hz. The results reveal that the absolute modulus passes through a maximum value with increasing NaDC concentration. The addition of amino acids increase...