Investigating the effect of the zwitterion/lactone equilibrium of rhodamine B on the cybotactic region of the acetonitrile/scCO2 cosolvent

Andreas Gahlmann; Kimberly D Kester; Steven G Mayer

doi:10.1021/jp0472818

Investigating the effect of the zwitterion/lactone equilibrium of rhodamine B on the cybotactic region of the acetonitrile/scCO2 cosolvent

J Phys Chem A. 2005 Mar 10;109(9):1753-7. doi: 10.1021/jp0472818.

Authors

Andreas Gahlmann¹, Kimberly D Kester, Steven G Mayer

Affiliation

¹ Department of Chemistry and Physics, University of Portland, 5000 N. Willamette Boulevard, Portland, Oregon 97203, USA.

PMID: 16833502
DOI: 10.1021/jp0472818

Abstract

We investigated the effect of adding acetonitrile to supercritical carbon dioxide (scCO(2)) in the presence of rhodamine B. This spectroscopic investigation of the scCO(2)/acetonitrile, rhodamine B/scCO(2), and rhodamine B/acetonitrile interactions revealed that rhodamine B, which possesses a temperature dependent equilibrium between a zwitterionic form and a neutral form, had a strong affect on the cybotactic region. To confirm that this effect was only dependent upon the rhodamine B/acetonitrile interactions and not merely due to the bulk-phase behavior of the scCO(2), we measured the compressibility of the scCO(2)/acetonitrile mixture and found it to be independent of the acetonitrile concentration to less than approximately 0.047 mol fraction. We fit the compressibility data using the Peng-Robinson equation of state because it is most appropriate for fluids in the region between 1.72 and 12.45 MPa and between 313 and 333 K.