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

Abstract

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

Heterogeneity in Lateral Distribution of Polycations at the Surface of Lipid Membrane: From the Experimental Data to the Theoretical Model

“…This effect was most clearly demonstrated in the case of PLL [ 40 ]. The same result is described in the work [ 76 ] for Lys8 and Arg8 oligopeptides. Polyarginine molecules turn out to be predominantly inserted into the membrane, while polylysine is partially exposed to the solution.…”

Role of Ions on the Surface-Bound Water Structure at the Silica/Water Interface: Identifying the Spectral Signature of Stability

“…The SFG spectrum of χ (3) is similar to that of bulk water, which is consistent with the diffuse layer exhibiting bulk-like hydrogen bonding with a small amount of net alignment due to the presence of the static electric field E 0 . This integral of the static electric field with respect to distance from the surface ( z ) is equal to the interfacial potential, Φ­( z ), and as such, many forms of the χ (3) method utilize Φ 0 , the potential at the zero-plane, which is normally positioned at the silica surface. Yet, recent work has shown the z -dependence of the sum-frequency light generated within the probe volume must also be considered. ,, Specifically, at low salt concentrations when the Debye length is substantial and the extent of water alignment approaches the coherence length of the incident light fields, significant destructive interference can arise between SF light generated at the surface and further into the bulk (a comparison of the Debye length as a function of salt concentration and the wavelength-dependent coherence length is provided in Figure S4).…”

Conjugate Acid–Base Interaction Driven Phase Transition at a 2D Air–Water Interface

“…Electronic structure methods could further aid in justifying the results of this statistical mechanics modeling results, in particular by providing estimates of the interaction strengths and optimized structure subject to the constraints of this air–water interface. , Molecular dynamics simulations may be valuable in better understanding fluctuation dynamics near the proposed critical point pH and for exploring ionic strength and added salt effects. The current rigid lattice model does not include surface tension as a measurable thermodynamic parameter.…”