A molecular understanding on the preferential and selective interactions of L-tryptophan, a major component of surfactant proteins, with 1,2-dipalmitoylsn-glycero-3-phosphocholine (DPPC) is important in the metabolic cycle of the pulmonary surfactant. In view of this, interfacial signals of interest in real time were tapped with aligned DPPC monolayers over a physiological tryptophan subphase using extremely surface sensitive 2D vibrational spectroscopy. Polarization-modulated and angle dependent Fourier transform infrared reflection absorption spectroscopy; (FT-IRRAS) of DPPC monolayers on water and L-tryptophan subphases depicted fine structure/conformation differences in the interaction modes evidenced from changes in the vibrational band intensities and frequencies under conditions of controlled 2D surface pressure. The computed 1:1 adducts of DPPC/H(2)O and DPPC/tryptophan in support of FT-IRRAS fine structure characteristics demonstrated binding in interfacial DPPC-tryptophan adducts to be driven by cation-pi interactions alongside hydrogen bonding of carbonyl and phosphate groups of the lipid with NH(3)(+) of the zwitterionic tryptophan. In situ spectroscopy enabled assignment of relative orientations of the equivalent -CH(2) functional groups from the polarized XY plane transition moments with component intensities of the split orthorhombic CH(2) mode. A larger molecular tilt of 37 degrees for the DPPC monolayer over tryptophan subphase in comparison with that over water (26 degrees) substantiated the DPPC headgroup interaction with tryptophan, complemented through delta (N(+)(CH(3))(3)), V(as) (PO(2)(-)), v(s) (PO(2)(-)), v(as) (C-N(+)-C), and v (C=O) vibrational features. The IRRAS spectral features of the DPPC 2D condensed phase showed distinct tryptophan-induced temperature dependent lattice phase transitions: hexagonal -> orthorhombic -> triclinic -> hexagonal packing of the hydrocarbon chains was noted over a subphase temperature range from 20 to 43 degrees C. The temperature dependent 2D DPPC lattice characteristics cited in this work will aid in understanding the impact of a temperature pulse toward the membrane functionality.