Interfacial concentrations of chloride and bromide in zwitterionic micelles with opposite dipoles: experimental determination by chemical trapping and a theoretical description.
Interfacial concentrations of chloride and bromide ions, with Li(+), Na(+), K(+), Rb(+), Cs(+), trimethylammonium (TMA(+)), Ca(2+), and Mg(2+) as counterions, were determined by chemical trapping in micelles formed by two zwitterionic surfactants, namely N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and hexadecylphosphorylcholine (HDPC) micelles. Appropriate standard curves for the chemical trapping method were obtained by measuring the product yields of chloride and bromide salts with 2,4,6-trimethyl-benzenediazonium (BF(4)) in the presence of low molecular analogs (N,N,N-trimethyl-propane sulfonate and methyl-phosphorylcholine) of the employed surfactants. The experimentally determined values for the local Br(-) (Cl(-)) concentrations were modeled by fully integrated non-linear Poisson Boltzmann equations. The best fits to all experimental data were obtained by considering that ions at the interface are not fixed at an adsorption site but are free to move in the interfacial plane. In addition, the calculation of ion distribution allowed the estimation of the degree of ion coverage by using standard chemical potential differences accounting for ion specificity.
Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CEP 05508-900, SP, Brazil; Department of Pharmaceutical Technology, Institute of Pharmacy, Friedrisch Schiller Universität - Jena, 07743 Jena, Germany.
Tereza Pereira
TP
de Souza
Hernan
H
Chaimovich
Alfred
A
Fahr
Bianca
B
Schweitzer
Augusto
A
Agostinho Neto
Iolanda Midea
IM
Cuccovia
D001965:Bromides / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry*; D008823:Micelles; D008962:Models, Theoretical; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
D001965:Bromides; D002712:Chlorides; D008823:Micelles; D013501:Surface-Active Agents; D014867:Water