TITLE

Hydrogen-bonding molecular ruler surfactants as probes of specific solvation at liquid/liquid interfaces

AUTHOR(S)
Siler, A. Renee; Brindza, Michael R.; Walker, Robert A.
PUB. DATE
October 2009
SOURCE
Analytical & Bioanalytical Chemistry;Oct2009, Vol. 395 Issue 4, p1063
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
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. [Figure not available: see fulltext.]
ACCESSION #
44445306

 

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