Thermodynamic analysis and fluorescence imaging of homochiral amino acid-amino acid interactions at the air/water interface.
Surface pressure-molecular area (Π-A) isotherms and fluorescence microscopy were used to investigate the interactions between N-stearoyl-glutamic acid (l- and d-) and l-arginine at the air/water interface. N-stearoyl-glutamic acids (C18-Glu) with different chirality (l- and d-) were spread at the air-water interface onto subphases containing varied concentrations of l-arginine at pH 5. The apparent binding affinity of C18-Glu to l-arginine was obtained by fitting the plots of the change in mean molecular area of C18-Glu vs. l-arginine concentration. The thermodynamic properties of the binding events such as binding constant and Gibbs free energy were estimated from the binding curves. We found that N-stearoyl-l-glutamic acid (C18-l-Glu) had a stronger binding affinity to l-arginine as compared to N-stearoyl-d-glutamic acid (C18-d-Glu) at low to moderate surface pressures (below ∼22mN/m). The C18-d-Glu had stronger binding to l-arginine at higher surface pressure. Domains with different shapes in C18-l-Glu and C18-d-Glu monolayers were observed under a fluorescence microscope in situ at the air/water interface. Herein, we present a mechanism for C18-l-Glu and C18-d-Glu interacting with l-arginine at the air/water interface.
Department of Chemistry and Biochemistry, James Madison University, Harrisonburg, VA 22807, USA.
Melissa R
MR
Palmer
Justin M
JM
Hagerman
Leigh M
LM
Matano
Kelsey M
KM
DeWitt
Yanjie
Y
Zhang
D000388:Air / Q000032:analysis*; D000596:Amino Acids / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D013237:Stereoisomerism; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D000596:Amino Acids; D014867:Water
Amino acid surfactant; Amino acid–amino acid interaction; Fluorescence microscopy; Langmuir monolayer; Surface pressure-molecular area (Π-A) isotherm