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Zhang P, Pham T, Zheng X, Liu C, Plata PL, Král P, Bu W, Lin B, Liu Y. Spontaneous collapse of palmitic acid films on an alkaline buffer containing calcium ions. Colloids Surf B Biointerfaces 2020; 193:111100. [PMID: 32408262 DOI: 10.1016/j.colsurfb.2020.111100] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2020] [Revised: 04/27/2020] [Accepted: 04/28/2020] [Indexed: 10/24/2022]
Abstract
Understanding the interaction of ions with fatty acids is important to identify their roles in various bioprocesses and to build novel biomimetic systems. In this study, the molecular organization of palmitic acid (PA) films on alkaline buffer solutions (pH 7.4) with and without divalent Ca2+ was measured at a constant surface area using Langmuir troughs coupled with microscopy and X-ray interfacial techniques. Without Ca2+, PA molecules remained a monolayer organization; however, with Ca2+, formation of the inverted bilayers of PA-Ca2+ superstructures caused a spontaneous 2D to 3D transformation under no compression due to the strong interaction between PA and the divalent cation. Self-assembly of this highly-organized inverted bilayer superstructure involved a two-step process of nucleation and nuclei growth. During nucleation, densely packed PA and Ca2+ monolayer firstly corrugated and some of PA and Ca2+ molecules ejected out from the monolayer; the ejected molecules then reorganized and formed the inverted bilayer nuclei. Nucleation was followed by nuclei growth, during which PA and Ca2+ in the monolayer kept integrating into the inverted bilayer structure through molecule migration and PA rotation around Ca2+.
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Affiliation(s)
- Pin Zhang
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL 60608, United States
| | - Tiep Pham
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL 60608, United States
| | - Xin Zheng
- Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, United States
| | - Chang Liu
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL 60608, United States
| | - Paola Leon Plata
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL 60608, United States
| | - Petr Král
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL 60608, United States; Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, United States; Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, United States; Department of Biopharmaceutical Sciences, University of Illinois at Chicago, Chicago, IL 60607, United States
| | - Wei Bu
- NSF's ChemMatCARS, University of Chicago, IL 60637, United States
| | - Binhua Lin
- NSF's ChemMatCARS, University of Chicago, IL 60637, United States
| | - Ying Liu
- Department of Chemical Engineering, University of Illinois at Chicago, Chicago, IL 60608, United States; Department of Biopharmaceutical Sciences, University of Illinois at Chicago, Chicago, IL 60607, United States; Department of Bioengineering, University of Illinois at Chicago, Chicago, IL 60607, United States.
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