Direct Measurement of Charge Reversal on Lipid Bilayers using Heterodyne-Detected Second Harmonic Generation Spectroscopy

Chang, Hak; Ohno, Paul E.; Liu, Yangdongling; Lozier, Emilie; Dalchand, Naomi; Geiger, Franz M.

doi:10.26434/chemrxiv.8678450

Cited by 12 publications

(30 citation statements)

References 7 publications

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“…Details of our HD-SHG spectrometer have been previously described. 11,[19][20][21][22] Solutions were flowed through a home-built Teflon sample cell at a rate of 5 mL min -1 for ten minutes for a complete exchange of the sample cell contents. This process was monitored using homodyne-detected SHG.…”

Section: Bmentioning

confidence: 99%

Divalent Ion Specific Outcomes on Stern Layer Structure and Total Surface Potential at the Silica:Water Interface

Geiger

2021

J. Phys. Chem. A

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The second-order nonlinear susceptibility, c (2) , in the Stern layer, and the total interfacial potential drop, F(0)tot, across the oxide:water interface are estimated from SHG amplitude and phase measurements for divalent cations (Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ ) at the silica:water interface at pH 5.8 and various ionic strengths. We find that interfacial structure and total potential depend strongly on ion valency. We observe statistically significant differences between the experimentally determined χ (2) value for NaCl and that of the alkali earth series, but smaller differences between ions of the same valency in that series. These differences are particularly pronounced at intermediate salt concentrations, which we attribute to the influence of hydration structure in the Stern layer. Furthermore, we corroborate the differences by examining the effects of anion substitution (SO4 2for Cl -). Finally, we identify that hysteresis in measuring the reversibility of ion adsorption and desorption at fused silica in forward and reverse titrations manifests itself both in Stern layer structure and in total interfacial potential for some of the salts, most notable CaCl2 and MgSO4, but less so for BaCl2 and NaCl.

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Section: Bmentioning

confidence: 99%

Divalent Ion Specific Outcomes on Stern Layer Structure and Total Surface Potential at the Silica:Water Interface

Geiger

2021

J. Phys. Chem. A

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“…Additional work is needed to determine the orientation of water molecules with the addition of polycations to our bilayer system by using heterodyne-detected SHG (HD-SHG). [64][65][66][67] This technique accesses the (/) and the potential-…”

Section: Polycations Bind To Bilayers With Comparable ∆Gadsmentioning

confidence: 99%

Electrostatics, Hydrogen Bonding, and Molecular Structure at Polycation and Peptide:Lipid Membrane Interfaces

Dalchand

Cui

Geiger

2019

ACS Appl. Mater. Interfaces

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Polycation and peptide modified surfaces represent opportunities for developing potentially novel biocidal materials in a growing effort to combat bacterial resistance to traditional bactericides. It is well known that the positive charge of these compounds is crucial to their function in biofouling prevention and as antimicrobials, however, methods for quantifying the number of positive charges on surface-bound polycations and peptides are necessary in order to predict, control, and optimize the design and therefore, the utility of these compounds. This Spotlight on Applications reports on such an approach that combines second harmonic generation (SHG) spectroscopy, quartz crystal microbalance with dissipation monitoring (QCM-D), and atomistic simulations to obtain mechanistic insight into polycation-membrane interactions using supported lipid bilayers (SLBs) as our model system. We find that at high surface coverage, the large polycations we surveyed feature a considerably smaller percentage of ionization when compared to the smaller polycations and peptides. At these high charge densities, we suspect a pKa shift of the charged groups to lower charge-charge repulsion as well as the formation of a loop-like conformation such that less monomeric units form contact-ion pairs with the bilayer. Our sum frequency generation (SFG) spectroscopy results complement our understanding of the

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“…To understand this unexpected outcome, we turned to another nonlinear optical technique that has been used to measure phase changes at the silica/water interface, namely nonresonant heterodyne-detected second harmonic generation (HD-SHG) spectroscopy. [78][79][80][81] As we demonstrated recently, the phase shift measured by HD-SHG is related to the total sum frequency phase shift under conditions where the Debye length is changing, 54 suggesting their origins are related.…”

Section: Resultsmentioning

confidence: 99%

Water Dipole Populations in the Electrical Double Layer and Their Contributions to the Total Interfacial Potential at Different Surface Charge Densities

Rehl

Ma²,

Parshotam

et al. 2022

Preprint

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The electric double layer governs the processes of all charged surfaces in aqueous solutions, however elucidating the structure of the water molecules is challenging for even the most advanced spectroscopic techniques. Here, we present the individual Stern layer and diffuse layer OH stretching spectra at the silica/water interface in the presence of NaCl over a wide pH range using a combination of vibrational sum frequency generation and heterodyned second harmonic generation techniques, streaming potential measurements, and the maximum entropy method. We find that the Stern layer water molecules and diffuse layer water molecules respond differently to pH changes: unlike the diffuse layer, whose water molecules remain net-oriented in one direction, water molecules in the Stern layer flip their net orientation as the solution pH is reduced from basic to acidic. We obtain an experimental estimate of the dipole potential contribution to the total potential drop across the insulator/electrolyte interface and find it to dominate over the Coulomb-only (Gouy-Chapman, Gouy-Chapman-Stern) contribution. We quantify how these contributions result in a considerable influence on the vibrational lineshapes. Our findings show that a purely Coulombic view is insufficient to accurately describe the electrical double layer over aqueous interfaces.

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Direct Measurement of Charge Reversal on Lipid Bilayers using Heterodyne-Detected Second Harmonic Generation Spectroscopy

Cited by 12 publications

References 7 publications

Divalent Ion Specific Outcomes on Stern Layer Structure and Total Surface Potential at the Silica:Water Interface

Divalent Ion Specific Outcomes on Stern Layer Structure and Total Surface Potential at the Silica:Water Interface

Electrostatics, Hydrogen Bonding, and Molecular Structure at Polycation and Peptide:Lipid Membrane Interfaces

Water Dipole Populations in the Electrical Double Layer and Their Contributions to the Total Interfacial Potential at Different Surface Charge Densities

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