In Situ Adsorption Studies of a 14-Amino Acid Leucine-Lysine Peptide onto Hydrophobic Polystyrene and Hydrophilic Silica Surfaces Using Quartz Crystal Microbalance, Atomic Force Microscopy, and Sum Frequency Generation Vibrational Spectroscopy

Abstract

The adsorption of a 14-amino acid amphiphilic peptide, LK14, which is composed of leucine (L, nonpolar) and lysine (K, charged), on hydrophobic polystyrene (PS) and hydrophilic silica (SiO2) was investigated in situ by quartz crystal microbalance (QCM), atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. The LK14 peptide, adsorbed from a pH 7.4 phosphate-buffered saline (PBS) solution, displayed very different coverage, surface roughness and friction, topography, and surface-induced orientation when adsorbed onto PS versus SiO2 surfaces. Real-time QCM adsorption data revealed that the peptide adsorbed onto hydrophobic PS through a fast (t < 2 min) process, while a much slower (t > 30 min) multistep adsorption and rearrangement occurred on the hydrophilic SiO2. AFM measurements showed different surface morphologies and friction coefficients for LK14 adsorbed on the two surfaces. Surface-specific SFG spectra indicate very different ordering of the adsorbed peptide on hydrophobic PS as compared to hydrophilic SiO2. At the LK14 solution/PS interface, CH resonances corresponding to the hydrophobic leucine side chains are evident. Conversely, only NH modes are observed at the peptide solution/SiO2 interface, indicating a different average molecular orientation on this hydrophilic surface. The surface-dependent difference in the molecular-scale peptide interaction at the solution/hydrophobic solid versus solution/hydrophilic solid interfaces (measured by SFG) is manifested as significantly different macromolecular-level adsorption properties on the two surfaces (determined via AFM and QCM experiments).

Sum frequency generation and solid-state NMR study of the structure, orientation, and dynamics of polystyrene-adsorbed peptides

“…The latter constraint, the distance of the α-carbon to the surface, can be estimated from the peptide sequence and the known orientation of the entire peptide on hydrophobic surfaces. It has been shown that the peptide assumes an α-helical secondary structure on polystyrene and that the leucine ensemble is generally oriented towards the interface while the lysines point towards the surrounding media (9,10,16,41,42). Leu1, Leu4, Leu8, and Leu11 have α-carbons close to the surface and are probably interacting strongly with the PS surface.…”

“…Sum frequency generation (SFG) spectroscopy has proven to be an increasingly powerful technique for probing protein films in situ at the solid-liquid interface (8)(9)(10)(11)(12)(13)(14)(15)(16). According to the "selection rules" of SFG, only molecular groups in proteins or peptides at an interface that have a net order will contribute to the measured signal (17).…”

“…According to the "selection rules" of SFG, only molecular groups in proteins or peptides at an interface that have a net order will contribute to the measured signal (17). Since surface interactions can introduce ordering in the binding regions of proteins and peptides, SFG is an excellent probe to identify the side chains involved in these binding events (9)(10)(11)15) and, in some cases, the orientation of adsorbed peptides (18). Backbone related amide modes, which are sensitive to conformation (19), can also determine the secondary structure of adsorbed peptides (14,20,21).…”

Revealing structural properties of the marine nanolayer from vibrational sum frequency generation spectra

“…Moreover, it can be considered unlikely that these porphyrine-carrying molecules exhibit the orientation preference required for SFG activity. Other NH containing compounds such as amino acids, peptides or amino sugars [Mermut et al, 2006;Aluwihare and Meador, 2008] are expected to yield signal around 3300 cm −1 [Shultz et al, 2000]. Consequently, (1) the presence of additional OH group containing compounds and/or (2) confined water molecules or water clusters residing in dense organic monolayers may serve as more probable explanations.…”

Sum Frequency Generation Spectroscopy in Biosensors Technology

“…Kim et al, 2004;Dreesen et al, 2004b;Paszti et al, 2004;X. Chen et al, 2005a;Clarke et al, 2005;Mermut et al, 2006;Phillips et al, 2007;York et al, 2007;Weidner et al, 2009Weidner et al, , 2010Baugh et al, 2010;Boughton et al, 2010;Ye et al, 2010;Nguyen et al, 2010). We believe it is important to summarise these protein related SFG studies and make it accessible to researchers in the fields of biosensors, biomaterials and biomedical diagnostic devices.…”