Surface-Assisted Transient Displacement Charge Technique. II. Effect of Gases on Photoinduced Charge Transfer in Self-Assembled Monolayers

Surface-assisted photoinduced transient displacement charge (SPTDC) technique was used to study charge transfer in self-assembled monolayers of 7-diethylaminocoumarin covalently linked to an oxide surface in the atmosphere of different gases. The dipole signal was found to be opposite to that in solution and dependent on the nature of the gas and its pressure. The results were explained by collision-induced relaxation that impedes uninhibited tilting of molecules onto the surface. Collisions with paramagnetic oxygen induce intersystem crossing to long-lived triplet dipolar states of coumarin with the rate close to half of that for the collision rate

Complex force-distance curves with multiple rupture peaks detected with WT alpha-synuclein (A, B) and A30P mutant (C, D).

<p>Red, green and blue lines on the graphs are calculated WLC curves using maxima of Gaussians determined from contour length distributions corresponding to 26, 36 and 47 nm (WT) and 22, 34 and 49 nm (A30P). E) Pie charts showing relative contribution of multiple rupture events to total rupture events: 31% (WT) and 15% (A30P).</p

Interaction model of alpha-synuclein molecules.

<p>The model describes three major peaks in the contour length histograms as identical sites in each monomer interacting with each other with the formation of a dimer. A) Position of the interacting site further from the C-terminus (point of attachment) results in longer contour length value. B) Positions at the beginning of the detected interaction sites. Colored arrows correspond to three detected interaction sites schematically shown in A), and the black arrow shows the position of the A30P mutation in alpha-synuclein; C), D) and E) superposition of representative force-distance curves for the detected rupture events corresponding to L_C1, L_C2 and L_C3, red, green and blue lines on the graphs are WLC curves calculated with L_C values from Fig. 4.</p

Statistical histograms of measured contour length values.

<p>A) Wild type, B) A30P mutant; the histograms were fit with Gaussian functions resulting in the following values of distribution maxima: 26 nm, 36 nm, 47 nm for WT and 22 nm, 34 nm, 49 nm for A30P mutant. Rupture force versus contour length plots C) Wild type, D) A30P mutant.</p

Schematic representation of the experimental approach.

<p>A) The unstructured form of alpha-synuclein immobilized on the tip and a substrate reveals no interaction. B) Misfolding of alpha-synuclein results in the formation of aggregation-prone conformation with elevated propensity of intermolecular interactions. C) A representative force-distance curve measured in the absence of spermidine. D) A representative force –distance curve with a rupture event in the presence of spermidine: (1) an adhesion peak due to short-range non-specific interactions between the tip and the surface, (2) gradual increase in force characteristic of polymer stretching, (3) complete rupture at 110 pN and (4) region where tip comes free from the surface. The inset shows worm-like chain fitting yielding contour length of 31 nm.</p

Effect of spermidine on the appearance of force-distance curves with A30P alpha-synuclein.

<p>Superposition of representative force-distance curves measured upon probing of interactions between A30P alpha-synuclein molecules: A) in the absence of spermidine (40 curves), B) with addition of 5 mM spermidine (58 curves).</p

Effect of spermidine on the appearance of force-distance curves with wild-type alpha-synuclein.

<p>Superposition of representative force-distance curves measured upon probing of interactions between wild type alpha-synuclein molecules: A) in the absence of spermidine (22 curves), B) with addition of 5 mM spermidine (26 curves).</p