Self-Assembly and Rearrangement of a Polyproline II Helix Peptide on Gold

Abstract

Polyproline peptide sequences have gained popularity as anchors for peptide-based self-assembled monolayers (SAMs) due to their attractive properties. In this work, peptides containing the polyproline II helix (PPII) conformation were designed and assembled on gold (Au). A quartz crystal microbalance with dissipation was used to characterize SAM formation kinetics and related properties. Peptides were designed with the sequence (GPPPPPG) 2 C. It was discovered that a biexponential adsorption and rearrangement model describes the binding kinetics of the PPII-containing peptide on Au. In this model, an initial reversible binding step is followed by an irreversible rearrangement step, given by parameter k t . This study found k t to be approximately 0.00064 s −1 for the PPII-containing peptides. Similarly, we found that the adsorption of the PPII-containing peptide on Au, given by ΔG ads , was thermodynamically favorable (−7.8 kcal mol −1 ) and comparable to other common thiol terminated SAMs on Au. Furthermore, we characterized SAM properties via QCM-D, Fouriertransform infrared (FTIR) spectroscopy, and electrochemical techniques to reveal high molecular density SAMs consisting of PPII helices. In addition, these SAMs were found to have high antifouling properties. Overall, this study characterizes the fundamental assembly mechanisms, particularly, rearrangement of PPII-containing peptides for the first time, which will be useful in the designing of future peptide-based SAMs with high surface coverage and antifouling properties.

Grafting of short elastin-like peptides using an electric field

“…3 ), where R is the gas constant and T is the temperature 56 . The ∆G ads seen in this work was − 7.69 ± 0.12 and − 7.78 ± 0.16 kcal/mol for charged and uncharged ELP respectively, typical of thiol-gold interactions 55 , 57 – 59 and indicative of a spontaneous process. There was minimal impact of the AEF on ∆G ads under the testing conditions of this work as seen in Fig.…”

“…2 ). Our previous work has shown this model to describe the adsorption of other peptides to a gold surface 55 . We note here that peptides could still transition under stimuli even when the rearrangement step is irreversible.…”

“…The module houses a Pt counter electrode plate that is 0.8 mm away from the gold working electrode. The hydrated mass uptake of the peptide layers grafted onto the gold surface was calculated from the recorded frequency by the QSense software as we have described previously using the Sauerbrey model 55 . The 3rd overtone (n) of the frequency and dissipation signals was selected for mass calculation, kinetics, and the DF analyses due to its stability and the noise-free nature of the data.…”

“…1 and 2 were conducted for QCM-D adsorption data using the third overtone in Python. The full biexponential fitting equation can be found in our previous work 55 . Specifically, the lmfit package was utilized to conduct nonlinear least squares fitting while reporting fitting parameters and model errors.…”

Secondary structure determines electron transport in peptides

“…Moving forward, our work could provide new avenues to understand the interplay between molecular charge transport and secondary structure in more complex peptide sequences with mixed amino acids and/or longer peptides. Proteins are candidate materials for fabricating functional molecular electronic devices due to biocompatibility, anti-fouling properties 68 , and tunable redox activity due to aromatic amino acids 69 . From this view, our work can provide further insights into understanding the role of higher order assembled structures on biological charge transport, which can be used to inform the design self-assembled bioelectronic materials.…”