Spontaneous collapse of palmitic acid films on an alkaline buffer containing calcium ions

Zhang, Pin; Pham, Tiep; Zheng, Xin; Liu, Chang; Plata, Paola Leon; Bu, Wei; Lin, Binhua; Liu, Ying

doi:10.1016/j.colsurfb.2020.111100

Cited by 8 publications

(12 citation statements)

References 41 publications

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“…48 Multivalent ions can however induce "charge-reversal" or spontaneous collapse of monolayers which have not been reported with monovalent ions. [50][51] In this context, effects of ion-ion correlation and ionmonolayer correlations have been described. 5,52 Further, specific ion-monolayer interactions such as hydrogen bonding and coordination bonds can lead to ion-specific interactions at the interface.…”

Section: Discussionmentioning

confidence: 99%

“…Recently, a spontaneous monolayer to inverted bilayer transformation of palmitic acid in the presence of calcium ions has been reported. 51 Divalent cations have also been shown to reduce the surface pressure at which stearic acid films collapse. 68 Interplay of ion-lipid interactions is especially important in the biophysics of cellular membranes where lipids affect selective ion transport and ions affect transbilayer lipid motions.…”

Section: Discussionmentioning

confidence: 99%

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Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

Nayak

Kumal

Uysal

2021

Preprint

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Amphiphilic lipid-ion interactions at aqueous interfaces drive the assisted ion transport in various biological and industrial systems. In chemical separations of heavy elements, lipids coordinate metal ions and solubilize them in an organic phase. Direct observation of lipid-metal interactions is highly difficult at the buried oil/water interface, and is accessible with limited experiments. Here, we demonstrate that inverted bilayer structures previously observed at oil/aqueous interfaces can also be formed at the air/aqueous interface. This facilitates the easier study of lipid-ion interactions over a wide range of parameters with multiple probes, including synchrotron X-ray reflectivity (XR), X-ray fluorescence near total reflection (XFNTR), and vibrational sum-frequency generation spectroscopy (VSFG). The formation of bilayers is highly sensitive to the metal ion charge density. While Lu3+ (115 C/mm3) lead to bilayer formation, Nd3+ (82 C/mm3) and Sr2+ (33 C/mm3) lead to monolayers. By introducing Lu3+ ions to preformed lipid monolayers, we extract kinetic parameters corresponding to monolayer to inverted bilayer conversion. Temperature-dependent studies show Arrhenius behavior with an energy barrier of 40 kcal/mol. The kinetics of monolayer to inverted bilayer conversion is also affected by the presence of background salts where thiocyanate accelerates the conversion more than nitrate does. Our results show the outsized importance of ion-specific effects on interfacial structure and kinetics, pointing to their role in chemical separation methods. Finally, this model system can be used to study a wide variety of lipid-ion interactions, opening a new avenue in molecular-scale understanding of these important systems.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

Nayak

Kumal

Uysal

2021

Preprint

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“…The X-ray wavelength was 1.24 Å. Details of the experimental setup were described in our previous publications. − Briefly, a custom-made Langmuir trough (78 mm × 177.6 mm) with a single barrier was filled with 60 mL of PBS buffer. The trough is placed inside a gastight box.…”

Section: Methodsmentioning

confidence: 99%

“…Synchrotron X-ray reflectivity (XR) and grazing-incidence diffraction (GIXD) are powerful techniques to reveal the molecular interaction between the drug and lipid molecules, which provide the fundamental information for the judicious design of liposomal formulations embedding amphiphiles with high drug loading. We have previously employed XR and GIXD to reveal the spontaneous collapsing of the fatty acid after enzyme-catalyzed degradation of the phospholipid and evaluated the effects of polyethylene glycol (PEG) on enzyme adsorption and lipid degradation and reorganization. , By integrating a Langmuir trough with the synchrotron X-ray liquid surface scattering techniques, we systematically studied the monolayer packing of 5-FCPal and various lipids at the air–water interface. Five representative saturated and unsaturated lipids of different headgroup charges were employed in the study, including lipids with positively charged head groups (i.e., 1,2-stearoyl-3-trimethylammonium-propane (DSTAP) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)), neutral zwitterionic head groups (i.e., 1,2-dipalmitoyl- sn -glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC)), and negatively charged head groups (i.e., 1,2-dipalmitoyl- sn -glycero-3-phospho-(1′-rac-glycerol) (DPPG)).…”

Section: Introductionmentioning

confidence: 99%

Knowledge-Based Design of 5-Fluororacil Prodrug Liposomal Formulation: Molecular Packing and Interaction Revealed by Interfacial Isotherms and X-ray Scattering Techniques

et al. 2021

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Prodrugs and nanoformulations are two effective strategies for sustained drug release and targeting drug delivery. In this study, we combined the two strategies to judiciously design the liposome formulation incorporating an amphiphilic prodrug of 5fouroracil (5-FU), named 5-FCPal, for sustained drug release and enhanced bioavailability. 5-FCPal is an analogue of capecitabine (N 4 -pentyloxycarbonyl-5′-deoxy-5-fluorocytidine, Xeloda) by substituting the pentyl group at the N 4 position with the palmityl. The amphiphilic molecule of 5-FCPal can self-assemble with the phospholipids to form stable vesicle structures with high drug loading. Although lipid vesicles have been widely studied and commercially used for clinical applications, because of the enormous options of the lipids and the equitable balance of hydrophobicity and bioavailability, it is essential to fundamentally understand the molecular interactions when designing and optimizing the liposomal prodrug formulations. We report the study of using X-ray liquid surface scattering techniques integrated with a Langmuir trough to explicitly reveal the interfacial behavior of the monolayer membrane of 5-FCPal with various saturated and unsaturated lipids with positively charged, neutral, and negatively charged head groups. More specifically, interfacial packing of the molecules was quantified using interfacial isotherms, X-ray reflectivity (XR), and grazingincidence diffraction (GIXD). The results indicate that the interactions between the prodrug and the cationic lipids are most favorable. The highest drug loading is quantified by increasing the molar ratio of the prodrug until stable monolayer structures were disrupted by the multiple-layer domain of prodrug aggregates. Stable liposomes of 100 nm with 50% drug loading of 5-FCPal were generated based on the findings from the X-ray studies.

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“…XR and GIXD experiments were conducted using a Langmuir trough integrated with the synchrotron X-ray beamline at the National Science Foundation’s (NSF’s) ChemMatCARS (sector 15C of Advanced Photon Sources) at Argonne National Laboratory. Details of the experimental setup were described in our previous studies. − The X-ray wavelength was 1.24 Å, and all experiments were conducted at about 22.7 °C.…”

Section: Materials and Methodsmentioning

confidence: 99%

Impeded Molecular Reorganization by Polyethylene Glycol Conjugation Revealed by X-ray Reflectivity and Diffraction Measurements

et al. 2020

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Polyethylene glycol (PEG) coatings have been widely applied in pharmaceutical and biomedical systems to prevent nonspecific protein absorption, increase vesicle blood circulation time, and sustain drug release. This study systematically investigated the planar interfacial organization of phospholipid monolayers containing various amounts of PEG conjugations before and after enzyme-catalyzed degradation of the lipids using X-ray reflectivity and grazing incidence X-ray diffraction techniques. Results showed that attaching PEG to the headgroup of the lipids up to 15 mol % had limited effects on molecular packing of the lipid monolayers in the condensed phase at the gas−liquid interface and negligible effects on the enzyme adsorption to the interface. After enzyme-catalyzed degradation, equimolar fatty acids and lyso PC were generated. The fatty acids together with the subphase Ca 2+ self-assembled into highly organized multilayer domains at the interface. The X-ray measurements unambiguously revealed that the densely packed PEG markedly hindered microphase separation and formation of the palmitic acid−Ca 2+ complexes.

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Spontaneous collapse of palmitic acid films on an alkaline buffer containing calcium ions

Cited by 8 publications

References 41 publications

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

Spontaneous and Ion-Specific Formation of Inverted Bilayers at Air/Aqueous Interface

Knowledge-Based Design of 5-Fluororacil Prodrug Liposomal Formulation: Molecular Packing and Interaction Revealed by Interfacial Isotherms and X-ray Scattering Techniques

Impeded Molecular Reorganization by Polyethylene Glycol Conjugation Revealed by X-ray Reflectivity and Diffraction Measurements

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