Interfacial Chemical Interactions Between Fine Carbonaceous Particles,polycyclic Aromatic Hydrocarbons And Pulmonary Surfactants

Atmospheric particulate matter is the primary pollutant affecting urban air quality,especially the particles with an aerodynamic diameter of less than or equal to2.5 microns(PM_2.5),i.e.fine particles,which affect air quality seriously and the concentration is much higher than the national average level.The composition of fine particles is complex,which is mainly composed of carbonaceous particles,mineral particles,metal particles and fly ash particles.Carbonaceous particles are an important component of fine particles,which account for a high proportion（as much as 50%）.Due to the small particle size and large specific surface area,carbonaceous particles are an important carrier of many pollutants,which can adsorb many toxic and harmful substances such as polycyclic aromatic hydrocarbons（PAHs）and heavy metals.Among them,PAHs can accumulate in tissues and have teratogenic and carcinogenic effects on human body due to the strong lipophilicity.Carbonaceous particles can cause respiratory diseases such as pneumonia and pulmonary fibrosis.However,the mechanism of the toxicity is not clear.Pulmonary surfactant（PS）film is the last barrier for foreign pollutants to enter the blood circulation system through respiratory tract.Once the particles reach the alveoli,they will first contact with the PS film.This interaction represents the initial biochemical reaction of the particles in the lung.To clarify the interfacial chemical interaction between carbonaceous fine particles and PS film is a key step to understand the biological activity and toxicity of carbonaceous fine particles.In this study,1,2-dipalmitoyl-sn-glycero-3-phosphocholine（DPPC）,1-palmitoyl-2-oleyl-sn-glycerol-3-phosphocholine（POPC）and self-extracted porcine lung surfactant were selected as the PS film models to study the interaction between carbonaceous fine particles（carbon nanoparticles,diesel exhaust particles）,PAHs and PS film.Firstly,the phase behavior and thermodynamic structure of DPPC,POPC and porcine lung surfactant film were studied,and the interfacial rheology and mechanical properties of PS film were explored.Secondly,the effect of carbon nanoparticles on the interfacial properties of DPPC monolayers and the interaction mechanism were explored.Then,the solubilization of benzo[a]anthracene by DPPC and POPC was analyzed.Finally,taking diesel exhaust particles as the target pollutant,the interaction between diesel exhaust particles and DPPC monolayers was studied,including the changes of the interfacial properties of PS film caused by diesel exhaust particles,the effects of DPPC on the surface properties of diesel exhaust particles,and the solubilization of PAHs by DPPC.The main results are as follows:（1）DPPC,POPC and natural porcine lung PS at the gas-liquid interface are different in phase transition,mechanical properties and structure.It was found that there was a significant correlation between the phase behavior of lipid domain and the content of unsaturated phospholipid component POPC.In the presence of POPC,the interfacial stability of the mixed DPPC/POPC monolayers was reduced and the transformation of liquid expansion phase to liquid condensation phase was inhibited.According to the intermolecular interaction and Raman spectrum,the repulsion between DPPC and POPC is the main force and the stretching vibration of C-C skeleton is the key factor affecting the phase behavior and structure of the mixed DPPC/POPC system.（2）Carbon nanoparticles can influence the surface activity of DPPC monolayers,induce micropores and uneven thickness of DPPC monolayers.Molecular dynamics simulation results showed that there is a strong binding trend between carbon nanoparticles and DPPC molecules.The particles can spontaneously adsorb DPPC molecules,resulting in the increase of the average distance between DPPC molecules.The relaxation mechanism of carbon nanoparticles on DPPC monolayers is that the adsorption of carbon nanoparticles on DPPC molecules restricts the free movement of DPPC molecules,resulting in the decrease of DPPC bulk density.（3）Benzo[a]anthracene can significantly effect the interfacial stability of the mixed DPPC/POPC monolayers,which will weaken the deformation resistance and the energy dissipation increases in the compression-expansion process.Raman spectrum shows that the lateral coupling ability of acyl chains of DPPC and POPC was reduced in the presence of benzo[a]anthracene,which is an important reason for the change of mechanical properties of the mixed monolayers caused by benzo[a]anthracene.Meanwhile,DPPC/POPC mixed micelles can solubilize benzo[a]anthracene,and the solubilization ability is more obvious with the increase of the proportion of POPC.The interaction between benzo[a]anthracene and PS film not only inhibits the biophysical function of PS film,but also affects the dissolution and migration of benzo[a]anthracene,which will further increase the health risk of benzo[a]anthracene.（4）Diesel exhaust particles can reduce the surface pressure of DPPC monolayers and destroy the ultrastructure of DPPC monolayers.The adsorption of DPPC onto diesel exhaust particles surface can lead to the change of the chargeability and result in the agglomeration of diesel exhaust particles in aqueous medium.In addition,the solubilization of DPPC will desorb PAHs loaded by the particle,and the desorption amount is positively correlated with the hydrophobicity of PAHs.In conclusion,exposure to carbonaceous fine particles and PAHs,the interfacial rheology,mechanical properties and ultrastructure of PS film will be seriously affected,which will directly cause the damage of the physiological function of PS film,and induce the occurrence of lung diseases.In addition,PS film can in turn affect the dispersion state of particles,induce the desorption of PAHs loaded on the particles,and change the migration and transformation of PAHs in the lung,and even cause harm to other tissues and organs through entering blood circulation.