Hydrogen-bonding molecular ruler surfactants as probes of specific solvation at liquid/liquid interfaces |
| |
Authors: | A Renee Siler Michael R Brindza Robert A Walker |
| |
Institution: | (1) Department of Chemistry and Biochemistry, University of Maryland, College Park, College Park, MD 20742, USA; |
| |
Abstract: | Resonance-enhanced, second harmonic generation (SHG) is used to measure the electronic structure of solutes sensitive to specific
solvation adsorbed to liquid/liquid and liquid/solid interfaces. Here, specific solvation refers to solvent–solute interactions
that are directional and localized. N-methyl-p-methoxyaniline (NMMA) is a solute whose first allowed electronic transition wavelength remains almost constant (∼315 nm)
in non-hydrogen-bonding solvents regardless of solvent polarity. However, in hydrogen-bond-accepting solvents such as dimethylsulfoxide,
NMMA’s absorbance shifts to longer wavelengths (320 nm), whereas in hydrogen-bond-donating solvents (e.g., water), the absorbance
shifts to shorter wavelengths (∼300 nm). SHG experiments show that at alkane/silica interfaces, surface silanol groups serve
as moderately strong hydrogen-bond donors as evidenced by NMMA’s absorbance of 307 nm. At the carbon tetrachloride/water interface,
NMMA absorbance also shifts to slightly shorter wavelengths (298 nm) implying that water molecules at this liquid/liquid interface
are donating strong hydrogen bonds to the adsorbed NMMA solutes. In contrast, experiments using newly developed molecular
ruler surfactants with NMMA as a model hydrophobic solute and a hydrophilic, cationic headgroup imply that, as NMMA migrates
across an aqueous/alkane interface, it carries with it water that functions as a hydrogen-bond-accepting partner. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|