title: Experimental and molecular dynamics investigation into the amphiphilic nature of sulforhodamine B.
abstract: Sulforhodamine B (SRB), a common fluorescent dye, is often considered to be a purely hydrophilic molecule, having no impact on bulk or interfacial properties of aqueous solutions. This assumption is due to the high water solubility of SRB relative to most fluorescent probes. However, in the present study, we demonstrate that SRB is in fact an amphiphile, with the ability to adsorb at an air/water interface and to incorporate into sodium dodecyl sulfate (SDS) micelles. In fact, SRB reduces the surface tension of water by up to 23 mN/m, and the addition of SRB to an aqueous SDS solution induces a significant decrease in the cmc of SDS. Molecular dynamics simulations were conducted to gain a deeper understanding of these findings. The simulations revealed that SRB has defined polar "head" and nonpolar "tail" regions when adsorbed at the air/water interface as a monomer. In contrast, when incorporated into SDS micelles, only the sulfonate groups were found to be highly hydrated, suggesting that the majority of the SRB molecule penetrates into the micelle. To illustrate the implications of the amphiphilic nature of SRB, an interesting case study involving the effect of SRB on ultrasound-mediated transdermal drug delivery is presented.
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Baris E
authors.initials: BE
authors.lastname: Polat
authors.forename: Shangchao
authors.initials: S
authors.lastname: Lin
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Mendenhall
authors.forename: Brett
authors.initials: B
authors.lastname: VanVeller
authors.forename: Robert
authors.initials: R
authors.lastname: Langer
authors.forename: Daniel
authors.initials: D
authors.lastname: Blankschtein
mesh_terms: D005456:Fluorescent Dyes / Q000737:chemistry; D006801:Humans; D008823:Micelles; D056004:Molecular Dynamics Simulation; D010539:Permeability; D012235:Rhodamines / Q000737:chemistry* / Q000378:metabolism; D012867:Skin / Q000378:metabolism; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013500:Surface Tension
chemical_list: D005456:Fluorescent Dyes; D008823:Micelles; D012235:Rhodamines; C022027:lissamine rhodamine B; D012967:Sodium Dodecyl Sulfate