Evaluating the Impact of Carbon Nanoparticles on the Interfacial Properties of the Pulmonary Surfactant Film

Abstract

The interaction between carbon nanoparticles (CNs) and Langmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) as a model pulmonary surfactant (PS) film was studied to shed light on the physicochemical bases underlying the potential adverse effects associated with pollutant inhalation. The results indicated that the surface pressure-area isotherms of the DPPC monolayers shifted toward lower molecular areas, and the compression modulus was reduced in the presence of CNs, hindering the ability of the DPPC monolayers to reduce the surface tension. The relaxation process of the DPPC monolayers were influenced, and the surface morphology and the continuity of the monolayers were destroyed by the penetration of CNs into the DPPC monolayers. The molecular dynamics simulation revealed that particle incorporation into the DPPC monolayers reduced the packing density of the DPPC molecules, worsening the mechanical performance of the monolayers. This effect was attributed to the strong binding trend between the CNs and the DPPC molecules. These results demonstrated that CNs could alter the relaxation mechanisms of the PS film, and this may cause a modification of the inhaled particle transport at the PS film and contribute to adverse health effects in the respiratory system of workers involved in the CN production process.

Keywords: adsorption; carbon nanoparticles; interfacial properties; pulmonary surfactant; relaxation mechanisms.

Figure 1

Construction of the DPPC monolayers and CN model (a); the radial distribution of P-P atoms in the DPPC monolayers (b).

Figure 2

π-A isotherms of the DPPC monolayers over CNs subphases solution (C_CNs = 10 mg/L) (a) and π-A isotherms of the DPPC monolayers over NCP subphases solution (C_NCP = 0, 5, 10, 50 mg/L) (b); the inset shows the compressibility modulus values, C_S⁻¹, calculated from π-A isotherms for the DPPC monolayers with different NCP weight fraction.

Figure 3

Normalization analysis of the π-t relaxation curves of the DPPC monolayers in the presence of NCP.

Figure 4

Effect of the CNs on the surface topography of the DPPC monolayers. (a–f): BAM images of pure DPPC monolayers and DPPC monolayers spread onto subphases with different CNs. (a): pure DPPC monolayers; (b): DPPC monolayers above CNTs solutions at a concentration of 10 mg/L; (c): DPPC monolayers above NCP solutions at a concentration of 10 mg/L; (d–f) show the intensity diagram corresponding to (a–c); (g): AFM characterization and height change of the DPPC monolayers above NCP solutions at the concentrations of 0, 5, 10, and 50 mg/L, respectively.

Figure 5

Structural perturbation of the DPPC monolayers affected by CNs.

Figure 6

Characterization of the DPPC monolayers perturbation by deposited CN. (Time sequence of typical snapshots from the top view. The carbon nanoparticle was not shown for clarity).

Figure 7

Influence of CNs on the ordering degree of the DPPC monolayers. (a): changes to ordering parameters of DPPC monolayers; (b): structure of DPPC monolayers; (c): changes to DPPC monolayers structure caused by CNs disturbance; (d): the average distance between P atoms in DPPC monolayers with simulation time.

Figure 8

Adsorption energy of CN for the DPPC molecules.