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Eliminating Fatigue in Surface-Bound Spiropyrans.

ABSTRACT: This paper describes an experimental approach to eliminating the loss of reversibility that surface-bound spiropyrans exhibit when switched with light. Although such fatigue can be controlled in other contexts, on surfaces, the photochromic compounds are held in close proximity to each other and relatively few molecules modulate the properties of a device, leading to a loss of functionality after only a few switching cycles. The switching process was characterized by photoelectron spectroscopy and differences in tunneling currents in the spiropyran and merocyanine forms using eutectic Ga-In. Self-assembled monolayers comprising only the photochromic compounds degraded rapidly, while mixed monolayers with hexanethiol showed different behaviors depending on the relative humidity. Under dry conditions, no chemical degradation was observed and the switching process was reversible over at least 100 cycles. Under humid conditions, no degradation occurred, but the switching process became irreversible. The absence of degradation observed in mixed monolayers is ascribed to the lack of solvation, which increases the barrier to a key bond rotation past the available thermal energy. These results highlight important differences in the contexts in which photochromic compounds are utilized and demonstrate that they can be leveraged to extract device-relevant functionality from surface-bound switches by suppressing fatigue and irreversibility.

SUBMITTER: Kumar S

PROVIDER: S-EPMC6816012 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Eliminating Fatigue in Surface-Bound Spiropyrans.

Kumar Sumit S Soni Saurabh S Danowski Wojciech W Leach Isaac F IF Faraji Shirin S Feringa Ben L BL Rudolf Petra P Chiechi Ryan C RC

The journal of physical chemistry. C, Nanomaterials and interfaces 20190924 42

This paper describes an experimental approach to eliminating the loss of reversibility that surface-bound spiropyrans exhibit when switched with light. Although such fatigue can be controlled in other contexts, on surfaces, the photochromic compounds are held in close proximity to each other and relatively few molecules modulate the properties of a device, leading to a loss of functionality after only a few switching cycles. The switching process was characterized by photoelectron spectroscopy a ...[more]

PMID: 31673304

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Project description:The influence of surface topography on protein conformation and association is used routinely in biological cells to orchestrate and coordinate biomolecular events. In the laboratory, controlling the surface curvature at the nanoscale offers new possibilities for manipulating protein-protein interactions and protein function at surfaces. We have studied the effect of surface curvature on the association of two proteins, α-lactalbumin (α-LA) and β-lactoglobulin (β-LG), which perform their function at the oil-water interface in milk emulsions. To control the surface curvature at the nanoscale, we have used a combination of polystyrene (PS) nanoparticles (NPs) and ultrathin PS films to fabricate chemically pure, hydrophobic surfaces that are highly curved and are stable in aqueous buffer. We have used single-molecule force spectroscopy to measure the contour lengths Lc for α-LA and β-LG adsorbed on highly curved PS surfaces (NP diameters of 27 and 50 nm, capped with a 10 nm thick PS film), and we have compared these values in situ with those measured for the same proteins adsorbed onto flat PS surfaces in the same samples. The Lc distributions for β-LG adsorbed onto a flat PS surface contain monomer and dimer peaks at 60 and 120 nm, respectively, while α-LA contains a large monomer peak near 50 nm and a dimer peak at 100 nm, with a tail extending out to 200 nm, corresponding to higher order oligomers, e.g. trimers and tetramers. When β-LG or α-LA is adsorbed onto the most highly curved surfaces, both monomer peaks are shifted to much smaller values of Lc. Furthermore, for β-LG, the dimer peak is strongly suppressed on the highly curved surface, whereas for α-LA the trimer and tetramer tail is suppressed with no significant change in the dimer peak. For both proteins, the number of higher order oligomers is significantly reduced as the curvature of the underlying surface is increased. These results suggest that the surface curvature provides a new method of manipulating protein-protein interactions and controlling the association of adsorbed proteins, with applications to the development of novel biosensors.

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Eliminating Fatigue in Surface-Bound Spiropyrans.

Publications

Eliminating Fatigue in Surface-Bound Spiropyrans.

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