Adsorption kinetics of l-glutathione on gold and structural changes during self-assembly: an in situATR-IR and QCM study

Abstract

The adsorption of L-glutathione (g-Glu-Cys-Gly) from ethanol on gold surfaces was studied in situ by both attenuated total reflection infrared (ATR-IR) spectroscopy and using a quartz crystal microbalance (QCM). The molecule is firmly anchored to the gold surface through the thiol group. Different IR signals of adsorbed L-glutathione, notably the amide I and n(-COOH), show significantly different behavior with time, which reveals that their increase is not related to adsorption (mass uptake) alone. This indicates that structural transformations take place during the formation of the self-assembled monolayer (SAM). In particular, the intensity of the acid signal increases quickly only within the first couple of minutes. The complexity of the selfassembling process is confirmed by QCM measurements, which show fast mass uptake within about 100 s followed by a considerably slower regime. The structural change superimposed on the mass uptake is, based on the in situ time-resolved ATR-IR measurements, assigned to the interaction of the acid group of the Gly moiety with the surface. The latter group is protonated in ethanol but deprotonates upon interaction with the gold surface. The protonation-deprotonation equilibrium is sensitive to external stimuli, such as the presence of dissolved L-glutathione molecules. The interaction of the acid group with the surface and concomitant deprotonation proceeds via two distinguishable steps, the first being a reorientation of the molecule, followed by the deprotonation.

Modeling two-rate adsorption kinetics: Two-site, two-species, bilayer and rearrangement adsorption processes

“…A particularly common occurrence is what appears to be a two-rate type process, where a fast initial adsorption step is followed by a slower stage of adsorption before equilibrium is reached. This is generally not explained by any of the 'traditional' isotherms listed above, and so a range of new models have arisen in the last few decades in an attempt to provide a physical rationalization for the behavior seen [6][7][8][9][10][11][12][13]. Typically, the two-rate adsorption behavior can be a result of four possibilities (or a combination of them) -two-sites with different energies [14][15][16][17][18], two species with different adsorption rate constants (or diffusion coefficients) [19], rearrangement of adsorbed molecules on the surface [20][21][22][23] or bilayer adsorption [24][25][26][27][28].…”

Molecular Dynamics Simulations and NMR Experimental Study of Oxidized Glutathione in Aqueous Solution

“…It was demonstrated that GSSG assumes a head-to-tail conformation in solution at neutral pH. Using attenuated total reflectance infrared spectroscopy and quartz crystal microbalance analysis, Bieri et al [18] found that the protonation-deprotonation equilibrium was sensitive to external stimuli, such as the presence of dissolved L-glutathione molecules. Lyon and Atkins [19] studied the self-assembly and gelation of oxidized glutathione in organic solvents.…”

“…Research has been focused on GSH and GSSG in recent years [17][18][19][20][21][22][23][24][25][26][27][28]. Molecular dynamics (MD) simulations and NMR techniques are often used to study the structures and properties of biochemical molecules in solutions [17][18][19][20][21]. Potentiometric and NMR spectroscopic measurements were performed by Krezel et al [17] to study protonation and Zn(II) binding properties of GSSG and a series of nine analogs with C-terminal modifications.…”

“…The GSH/GSSG system is a very important intracellular oxidationreduction buffer, which can provide protection against carcinogenic or oxidative damage [11][12][13][14][15][16]. Research has been focused on GSH and GSSG in recent years [17][18][19][20][21][22][23][24][25][26][27][28]. Molecular dynamics (MD) simulations and NMR techniques are often used to study the structures and properties of biochemical molecules in solutions [17][18][19][20][21].…”

Nano-Mechanical Transduction of Polymer Micro-Cantilevers to Detect Bio-Molecular Interactions

“…GSH, a tripeptide from glycine, cysteine and glutamate, is the most abundant non-protein thiol-bearing molecule of mammalian cells and is involved in many physiological processes [15][16][17]. GSH is known to interact with ions and heavy metals, and is capable to organize on gold surfaces as self assembled monolayers (SAMs) [18]. SAMs serve as sensitive sensing layer for cantilever based sensors.…”