Let there be light: stability of palmitic acid monolayers at the air/salt water interface in the presence and absence of simulated solar light and a photosensitizer

Shrestha, Mona; Luo, Man; Li, Yingmin; Xiang, Bo; Xiong, Wei; Grassian, Vicki H.

doi:10.1039/c8sc01957f

Cited by 42 publications

(58 citation statements)

References 42 publications

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“…4,7,17 Fatty acids present in sea surface microlayer are released primarily during the lysis of phospholipid cellular membranes of marine organisms. 11,14 Saturated fatty acids, particularly palmitic acid (PA) and stearic acid (SA), contribute significantly to the organic coating of sea salt particles, 11,[18][19] with arachidic acid (AA) showing a relatively lower abundance. 20 On the other hand, a former analysis of marine aerosols collected over the Mediterranean Sea using a five-stage cascade impactor, found the existence of fatty acid methyl esters from C14 to C34 in SSAs, among which, methyl palmitate (MP) and methyl stearate (MS) were found to be predominant.…”

Section: Introductionmentioning

confidence: 99%

Insights into the Headgroup and Chain Length Dependence of Surface Characteristics of Organic-Coated Sea Spray Aerosols

Cheng

Tsona

et al. 2019

ACS Earth Space Chem.

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The structure of sea spray aerosols (SSAs) has been described as a saline core coated by organic surfactants. The presence of surface-active compounds at the air-water interface can have a large impact on physical, chemical and optical properties of SSAs. The surfactant molecules chosen for this study, palmitic acid (PA), stearic acid (SA), arachidic acid (AA), methyl palmitate (MP), methyl stearate (MS) and methyl arachidate (MA), were used to investigate the effect of alkyl chain-length, head-groups and sea salts on the surface properties of these monolayers. A Langmuir trough was used for measuring surface pressure−area (π−A) isotherms to reveal macroscopic phase behavior of the surface films at the air-water interface. Infrared reflection absorption spectroscopy (IRRAS) was employed to have a molecular-level understanding of the interfacial molecular organization. The π−A isotherms indicated that sea salts, present in the subphase, exert a strong condensing effect on fatty acid monolayers, while exerting expanding effect on fatty acid methyl ester monolayers, which was confirmed by results from IRRAS experiments. IRRAS further revealed that the alkyl chains were in an all-trans conformation, which can be evidenced by the relatively low νa(CH2) and νs(CH2) stretching frequencies. The conformational order changes in the alkyl chains of different film-forming species (C16 < C18 < C20) were directly revealed by analyzing the relative intensity of the νa(CH2) and νs(CH2) peaks in the C-H stretching region. Thus, all the three factors alter the phase behavior and molecular packing of the monolayers at the air-aqueous interface.

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Section: Introductionmentioning

confidence: 99%

Insights into the Headgroup and Chain Length Dependence of Surface Characteristics of Organic-Coated Sea Spray Aerosols

Cheng

Tsona

et al. 2019

ACS Earth Space Chem.

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“…Both the chemical transformation and polymerization of gas and condensed-phase low-molecular-weight VOCs are the secondary sources of HULIS (Stone et al, 2009;Gelencser et al, 2002). The interfacial photochemistry of a palmitic acid monolayer involving humic acid as a photosensitizer has been recently investigated (Shrestha et al, 2018). Therefore, the photochemistry of such organic films is attracting increasing attention, as the photosensitized reaction initiated by atmospheric samples containing BrC has not been investigated and the associated mechanism is not understood.…”

Section: Introductionmentioning

confidence: 99%

Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air-aqueous interface

Li¹,

Jiang²,

George³

et al. 2019

Preprint

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Abstract. Photosensitizing compounds containing brown carbon can absorb UV light and transfer that energy to low volatile organic compounds at the surface of aqueous particles. To better understand the reactivity and photochemical aging processes of organic coating on the aqueous aerosol surface, we have simulated the photosensitized reaction of organic films made of several long chain fatty acids in a Langmuir trough in the presence or absence of irradiation. Several chemicals (imidazole-2-carboxaldehyde and humic acid), PM2.5 samples collected from the field and secondary organic aerosols samples generated from a simulation chamber were used as photosensitizers to be involved in the photochemistry of the organic films. Stearic acid, elaidic acid, oleic acid and two different phospholipids with the same carbon chain length and different degrees of saturation i.e., 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC) were chosen as the common organic film-forming species in this analysis. The double bond (trans and cis) in unsaturated organic compounds has an effect on the surface area of the organic monolayer. The OA monolayer possessing a cis double bond in an alkyl chain is more expanded than EA monolayers on artificial seawater that contain a photosensitizer. Monitoring the change in the relative area of DOPC monolayers has shown that DOPC does not react with photosensitizers under dark conditions. Instead, the photochemical reaction initiated by the excited photosensitizer and molecular oxygen can generate hydroperoxidation in the DOPC monolayers, accompanied by an increase in the molecular area. The DSPC monolayers did not yield any photochemical oxidized products under the same conditions. The spectra measured with polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS) were also consistent with the results of a surface pressure-area isotherm. Here, a reaction mechanism explaining these observations is presented and discussed. The results will contribute to our understanding of the processing of organic aerosol aging that controls the aerosol composition.

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“…Among these techniques, PM-IRRAS has emerged as one of the leading methods for detailed analyses of monolayers at the airwater interface and can provide abundant information concerning lipid conformation, tilt, and headgroup structures (Du and Wang, 2007). This technique is currently an important in-situ method coupled to Langmuir trough to directly monitor the interfacial properties of natural aqueous aerosols under a simplified and controlled physicochemical environment (Shrestha et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

“…The presence of significant portions of fatty acids with saturated and unsaturated alkyl chains at the sea surface microlayer has been widely studied (Shrestha et al, 2018). Being single chain amphiphilic molecules with high surface activity, fatty acids can be transferred to marine aerosols during the bubble bursting process with higher efficiency relative to other less surface-active molecules (Cochran et al, 2016a).…”

Section: Introductionmentioning

confidence: 99%

“…Phospholipids from the marine biota are reported to be an important source of saturated fatty acids found in the SML, and at the interface of marine aerosols (Ellison et al, 1999;Zhang et al, 2016). Saturated fatty acids especially palmitic acid and stearic acid (SA) are known to be the major SSA film forming materials, and thus thoroughly studied as Langmuir monolayer in pure form or mixtures to elucidate their functions at interfaces of SSAs (Adams and Allen, 2013;Adams et al, 2016;Griffith et al, 2013;Shrestha et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Alterations in the surface properties of sea spray aerosols introduced by the presence of sterols

Cheng

Tsona

et al. 2019

Science of The Total Environment

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The mixed steric acid (SA)/sterol systems were used as sea spray aerosol mimics to get more insights into the alterations in surface properties of aerosols induced by sterols. By means of surface pressure (π)-area (A) isotherms and polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS), the effect of cholesterol (chol), stigmasterol (stig) and ergosterol (erg) on the lateral packing and chain conformation of SA monolayer was explored. The fact that the excess areas of mixing of the mixed monolayers exhibit significant deviations from ideally mixed film proves that, the sterols are miscible with SA in the whole range of the monolayer compositions and surface pressures. The lift-off areas in π-A isotherms were found to increase with increasing mole fraction of sterols, indicating that expulsive interactions exist between SA and sterols, which are more pronounced when the mole fraction of sterols is 0.7. In addition, the peak intensities of νa(CH2) and νs(CH2) in IRRAS spectra decrease with increasing sterols levels, which is consistent with our findings in the π-A isotherms, that the addition of sterols leads to a looser chain packing in SA monolayer. The proportion of gauche defects in SA monolayer induced by the sterols follows the order cholesterol < stigmasterol < ergosterol at a certain sterol level, as reflected by the decreasing peak intensities of νa(CH2) and νs(CH2). Consequently, the sterols generally give rise to considerable expanding effects on SA monolayer, which are particularly pronounced for stigmasterol and ergosterol, suggesting that the additional alkyl side chains and double bonds of the sterols play a role on disordering SA monolayer. The present study is likely to shed light on many boundary processes take place at the interface of SSAs, in particular, transport processes of water and trace gases across the interface.

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Let there be light: stability of palmitic acid monolayers at the air/salt water interface in the presence and absence of simulated solar light and a photosensitizer

Abstract: The stability of palmitic acid monolayers at the air/salt water interface changes in the presence of light and a photosensitizer.

Cited by 42 publications

References 42 publications

Insights into the Headgroup and Chain Length Dependence of Surface Characteristics of Organic-Coated Sea Spray Aerosols

Insights into the Headgroup and Chain Length Dependence of Surface Characteristics of Organic-Coated Sea Spray Aerosols

Photochemical aging of atmospherically reactive organic compounds involving brown carbon at the air-aqueous interface

Alterations in the surface properties of sea spray aerosols introduced by the presence of sterols

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