Probing Molecular Interactions between Surface-Immobilized Antimicrobial Peptides and Lipopolysaccharides <i>In Situ</i>

Xu, Shan; Reichart, Timothy; Xiao, Mengyuan; Lu, Tieyi; Mello, Charlene M.; Chen, Zhan

doi:10.1021/acs.langmuir.0c02492

Cited by 14 publications

(19 citation statements)

References 68 publications

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“…Sum frequency generation (SFG) vibrational spectroscopy has been demonstrated to be a suitable tool to understand the change of molecular structures of surfaces and interfaces. − SFG enables precisely measuring the molecular structure/behavior of surfaces/interfaces by its surface/interface-sensitive nature. − SFG has been extensively applied to study the surface and interfacial molecular structures of polymers, including various polymer adhesives. − ,− In this study, the atmospheric moisture effect on the surfaces of isocyanate-based primers was probed by SFG, and the molecular behaviors of such surfaces were correlated to the macroscopic properties to investigate the relationship. Different conditions in the experiments were set up in a variation of humidity levels and exposure time to understand the influences of their effects on the primer surfaces.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

et al. 2021

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A primer coating is engineered to facilitate compatibility between products like adhesives, sealants, and potting compounds and targeted substrates. Prolonged exposure of isocyanate-based primer surfaces to the environment is known to negatively affect the interfacial adhesion between itself and the products subsequently applied on top of it. However, the molecular behavior behind this observed phenomenon remained to be further investigated. In this study, sum frequency generation (SFG) vibrational spectroscopy, a nonlinear optical spectroscopic technique, was applied to study the surface of an isocyanate-based primer exposed to different environments at the molecular level. Atmospheric moisture was considered to be a potential factor in impairing the adhesion performance of the primer, and thus, time-and humidity-dependent experiments were executed to monitor the molecular behavior at the primer surface using SFG. In addition, 180°peel testing experiments were conducted to measure the adhesion properties of primers after being exposed to the corresponding conditions to correlate to SFG results and establish a chemical structure−macroscopic performance relationship. This study on the changes at the primer surface in different environments with varied humidity levels as a function of time aims to provide an in-depth understanding of the moisture effect on isocyanatebased primers. These learnings may also be helpful toward exploring a broader range of coatings and surface layers and improving customer product use guidelines.

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Section: Introductionmentioning

confidence: 99%

Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

et al. 2021

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“…SFG vibrational spectroscopy (or SFG in short) is a second-order nonlinear optical technique which is submonolayer surface sensitive because of its special selection rule: under the electric dipole approximation, SFG signal can only be generated from a medium with no inversion symmetry. − SFG probes the macroscopic second-order nonlinear susceptibility χ (2) of a material, while χ (2) is nonzero only for a sample with no inversion symmetry. − , Most bulk media are centrosymmetric, thus do not have SFG signal, while surfaces and interfaces lack inversion symmetry and can generate SFG signals. For a charged interface like silica–water interface, it is believed and shown that there are bulk (3) contributions from the electric double layer/diffuse layer near the silica–water interface.…”

Section: Experimental Sectionmentioning

confidence: 99%

“…Here we studied nonionic surfactants and water at the silica–surfactant solution interface. SFG is a surface-specific second-order nonlinear optical spectroscopy probing second-order nonlinear susceptibility χ (2) of a medium, which has been developed into a powerful tool to investigate surfaces and interfaces. − We have applied SFG to study a variety of complex surfaces and interfaces including biological molecules, polymers, as well as surfactants. ,− The silica–water interfaces have been extensively studied by SFG in various aspects. − Silanol groups on a silica surface can be deprotonated in an aqueous solution under neutral pH (SiOH ⇄ SiO – + H + ), which results in a negatively charged silica surface in contact with water. , Different surface structures of silica can form different types of hydrogen bonding with water at the buried silica–water interface, making water molecules ordered at the immediate silica–water interface (the nearest water layer on silica), which contribute to SFG signals. − …”

Section: Introductionmentioning

confidence: 99%

Effect of Surfactant Concentration and Hydrophobicity on the Ordering of Water at a Silica Surface

Shi

McMillan

et al. 2021

Langmuir

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The performance of nonionic surfactants is mediated by the interfacial interactions at the solid–liquid interface. Here we applied sum frequency generation (SFG) vibrational spectroscopy to probe the molecular structure of the silica–nonionic surfactant solution interface in situ, supplemented by quartz crystal microbalance with dissipation monitoring (QCM-D) and molecular dynamics (MD) simulations. The combined studies elucidated the effects of nonionic surfactant solution concentration, surfactant composition, and rinsing on the silica–surfactant solution interfacial structure. The nonionic surfactants studied include ethylene-oxide (EO) and butylene oxide (BO) components with different ratios. It was found that the CH groups of the surfactants at the silica–surfactant solution interfaces are disordered, but the interfacial water molecules are ordered, generating strong SFG OH signals. Solutions with higher concentrations of surfactant lead to a slightly higher amount of adsorbed surfactant at the silica interface, resulting in more water molecules being ordered at the interface, or a higher ordering of water molecules at the interface, or both. MD simulation results indicated that the nonionic surface molecules preferentially adsorb onto silanol sites on silica. A surfactant with a higher EO/BO ratio leads to more water molecules being ordered and a higher degree of ordering of water molecules at the silica–surfactant solution interface, exhibiting stronger SFG OH signal, although less material is adsorbed according to the QCM-D data. A thin layer of surfactants remained on the silica surface after multiple water rinses. To the best of our knowledge, this is the first time the combined approaches of SFG, QCM-D and MD simulation techniques have been applied to study nonionic surfactants at the silica–solution interface, which enhances our understanding on the interfacial interactions between nonionic surfactants, water and silica. The knowledge obtained from this study can be helpful to design the optimal surfactant concentration and composition for future applications.

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“…Sum frequency generation (SFG) vibrational spectroscopy is a second-order nonlinear optical technique with intrinsic interface sensitivity. − SFG has been extensively employed to study molecular structures of solid/liquid interfaces. − We have demonstrated that the valuable molecular information for polymer/solution interfaces obtained by SFG can contribute to the elucidation of interfacial behaviors of polymer, − water, − and biological molecules. ,− To gain fundamental understandings of the interfacial behaviors in CFRP, SFG was applied to characterize the molecular structures of carbon fiber/sizing solution and plastic/sizing solution interfaces in this study.…”

Section: Introductionmentioning

confidence: 99%

Interfacial Structure and Interfacial Tension in Model Carbon Fiber-Reinforced Polymers

et al. 2021

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Carbon fiber-reinforced plastics (CFRPs) are widely used materials with outstanding mechanical properties. The wettability between the polymer matrix and carbon fiber in the interphase region significantly influences the strength of the composite. Sizing agents consisting of multiple components are therefore frequently applied to improve wetting and interfacial adhesion between polymers and carbon fiber in CFRPs. However, the complex compositions of sizing solutions make detailed interpretations of their impacts on interfacial wetting difficult. In this work, surface-sensitive sum frequency generation (SFG) spectroscopy was utilized to characterize the sizing/polymer and sizing/carbon fiber interfacial structures to gain molecular-level understandings of the wetting improvements afforded by sizing. A mixture sizing solution containing polyethylenimine (PEI, adhesion promoter) and Lutensol (surfactant) was investigated when contacting nylon (model plastics), polypropylene (model plastics), and graphite (model carbon fiber). Our results demonstrated that although the addition of the surfactant led to an interfacial tension decrease (in comparison to pure PEI solution) on nylon and polypropylene, the interfacial tension was surprisingly increased on graphite, contrasting with the commonly accepted function of surfactants. SFG characterizations revealed the multilayer molecular structures at these buried interfaces. The peculiar interfacial tension increase at the graphite/sizing interface was then correlated to the strong amine−π interactions between PEI and graphite. PEI was therefore demonstrated to be an effective adhesion promoter for carbon fiber. This article reports the first investigation of (polymer + surfactant) complex structures at solid− liquid interfaces. The valuable structural insights obtained by SFG analysis enable more accurate understandings of the composition−wettability (structure−function) relationship. These detailed understandings of interactions between sizing and the substrates promote more informed and optimized selections of sizing formulae.

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Probing Molecular Interactions between Surface-Immobilized Antimicrobial Peptides and Lipopolysaccharides In Situ

Cited by 14 publications

References 68 publications

Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

Effect of Surfactant Concentration and Hydrophobicity on the Ordering of Water at a Silica Surface

Interfacial Structure and Interfacial Tension in Model Carbon Fiber-Reinforced Polymers

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