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Reactivity mapping with electrochemical gradients for monitoring reactivity at surfaces in space and time.

Krabbenborg SO, Nicosia C, Chen P, Huskens J - Nat Commun (2013)

Bottom Line: Because reaction kinetics is different at surfaces compared with solution, frequently, solution-characterization techniques cannot be used.For both systems, the kinetic data were spatially visualized in a two-dimensional reactivity map.In the case of the copper(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition, the reaction order (2) was deduced from it.

View Article: PubMed Central - PubMed

Affiliation: Molecular Nanofabrication Group, MESA+ Institute for Nanotechnology, University of Twente, PO Box 217, Enschede 7500 AE, The Netherlands.

ABSTRACT
Studying and controlling reactions at surfaces is of great fundamental and applied interest in, among others, biology, electronics and catalysis. Because reaction kinetics is different at surfaces compared with solution, frequently, solution-characterization techniques cannot be used. Here we report solution gradients, prepared by electrochemical means, for controlling and monitoring reactivity at surfaces in space and time. As a proof of principle, electrochemically derived gradients of a reaction parameter (pH) and of a catalyst (Cu(I)) have been employed to make surface gradients on the micron scale and to study the kinetics of the (surface-confined) imine hydrolysis and the copper(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition, respectively. For both systems, the kinetic data were spatially visualized in a two-dimensional reactivity map. In the case of the copper(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition, the reaction order (2) was deduced from it.

No MeSH data available.


Micron-scale surface ‘clicked’ gradient formation via a [Cu(I)] solution gradient.(a) Schematic representation of the electrochemical generation of a [Cu(I)] gradient in solution between the electrodes of an interdigitated electrode array, obtained via the reduction of Cu(II) to Cu(I) and oxidation of the resulting Cu(I) to Cu(II) at the cathode and anode, respectively. This solution gradient is transferred to a surface gradient by means of the electrochemically activated click reaction of a fluorescein-labelled alkyne to an azide monolayer, resulting in a surface-bound fluorescein dye gradient. (b) Fluorescence microscopy image of the resulting surface gradient, 1.0 mM fluorescein alkyne, 1.0 mM CuSO4 salt in dimethylsulphoxide, ΔV=1 V, 4 min reaction time (50 μm electrodes, 100 μm gap). Scale bar, 100 μm. (c) Fluorescence microscopy image, after overlay of images made using the green (λexc=495 nm, λem≥520 nm) and blue (λexc=350 nm, λem≥420 nm) filters, of a bi-component surface chemical gradient by means of the ‘e-click’ (2 min) of a fluorescein-labelled alkyne followed by a switch of the polarity of the electrodes and performing a further ‘e-click’ (2 min) of a coumarin-labelled alkyne. Scale bar, 200 μm. (d) Fluorescence intensity profiles versus distance from the cathode visualizing the resulting dye gradient for different reaction times (raw data, obtained ex situ).
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f4: Micron-scale surface ‘clicked’ gradient formation via a [Cu(I)] solution gradient.(a) Schematic representation of the electrochemical generation of a [Cu(I)] gradient in solution between the electrodes of an interdigitated electrode array, obtained via the reduction of Cu(II) to Cu(I) and oxidation of the resulting Cu(I) to Cu(II) at the cathode and anode, respectively. This solution gradient is transferred to a surface gradient by means of the electrochemically activated click reaction of a fluorescein-labelled alkyne to an azide monolayer, resulting in a surface-bound fluorescein dye gradient. (b) Fluorescence microscopy image of the resulting surface gradient, 1.0 mM fluorescein alkyne, 1.0 mM CuSO4 salt in dimethylsulphoxide, ΔV=1 V, 4 min reaction time (50 μm electrodes, 100 μm gap). Scale bar, 100 μm. (c) Fluorescence microscopy image, after overlay of images made using the green (λexc=495 nm, λem≥520 nm) and blue (λexc=350 nm, λem≥420 nm) filters, of a bi-component surface chemical gradient by means of the ‘e-click’ (2 min) of a fluorescein-labelled alkyne followed by a switch of the polarity of the electrodes and performing a further ‘e-click’ (2 min) of a coumarin-labelled alkyne. Scale bar, 200 μm. (d) Fluorescence intensity profiles versus distance from the cathode visualizing the resulting dye gradient for different reaction times (raw data, obtained ex situ).

Mentions: A schematic representation of the second (CuAAC) reaction studied is shown in Fig. 4a, in which a [Cu(I)] gradient is applied on top of an azide-terminated silane layer that is attached to the glass substrate areas between the electrodes of an interdigitated electrode array. The Cu(I) catalyst is formed in situ by an one-electron reduction of already present Cu(II)36, at the cathode (source), whereas oxidation of the generated Cu(I) back to Cu(II) at the anode (sink) makes sure a stable gradient is formed. The solution gradient of [Cu(I)] is then exploited in the electrochemically activated CuAAC (‘e-click’) of an alkyne from solution to the azide monolayer resulting in a surface gradient. The reaction is monitored ex situ via immobilization of an alkyne-modified fluorescein onto the azide-terminated monolayer. The rate of this reaction is expected to be the highest close to the cathode, at which electrode the reduction of Cu(II) to Cu(I) is expected to occur.


Reactivity mapping with electrochemical gradients for monitoring reactivity at surfaces in space and time.

Krabbenborg SO, Nicosia C, Chen P, Huskens J - Nat Commun (2013)

Micron-scale surface ‘clicked’ gradient formation via a [Cu(I)] solution gradient.(a) Schematic representation of the electrochemical generation of a [Cu(I)] gradient in solution between the electrodes of an interdigitated electrode array, obtained via the reduction of Cu(II) to Cu(I) and oxidation of the resulting Cu(I) to Cu(II) at the cathode and anode, respectively. This solution gradient is transferred to a surface gradient by means of the electrochemically activated click reaction of a fluorescein-labelled alkyne to an azide monolayer, resulting in a surface-bound fluorescein dye gradient. (b) Fluorescence microscopy image of the resulting surface gradient, 1.0 mM fluorescein alkyne, 1.0 mM CuSO4 salt in dimethylsulphoxide, ΔV=1 V, 4 min reaction time (50 μm electrodes, 100 μm gap). Scale bar, 100 μm. (c) Fluorescence microscopy image, after overlay of images made using the green (λexc=495 nm, λem≥520 nm) and blue (λexc=350 nm, λem≥420 nm) filters, of a bi-component surface chemical gradient by means of the ‘e-click’ (2 min) of a fluorescein-labelled alkyne followed by a switch of the polarity of the electrodes and performing a further ‘e-click’ (2 min) of a coumarin-labelled alkyne. Scale bar, 200 μm. (d) Fluorescence intensity profiles versus distance from the cathode visualizing the resulting dye gradient for different reaction times (raw data, obtained ex situ).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3644076&req=5

f4: Micron-scale surface ‘clicked’ gradient formation via a [Cu(I)] solution gradient.(a) Schematic representation of the electrochemical generation of a [Cu(I)] gradient in solution between the electrodes of an interdigitated electrode array, obtained via the reduction of Cu(II) to Cu(I) and oxidation of the resulting Cu(I) to Cu(II) at the cathode and anode, respectively. This solution gradient is transferred to a surface gradient by means of the electrochemically activated click reaction of a fluorescein-labelled alkyne to an azide monolayer, resulting in a surface-bound fluorescein dye gradient. (b) Fluorescence microscopy image of the resulting surface gradient, 1.0 mM fluorescein alkyne, 1.0 mM CuSO4 salt in dimethylsulphoxide, ΔV=1 V, 4 min reaction time (50 μm electrodes, 100 μm gap). Scale bar, 100 μm. (c) Fluorescence microscopy image, after overlay of images made using the green (λexc=495 nm, λem≥520 nm) and blue (λexc=350 nm, λem≥420 nm) filters, of a bi-component surface chemical gradient by means of the ‘e-click’ (2 min) of a fluorescein-labelled alkyne followed by a switch of the polarity of the electrodes and performing a further ‘e-click’ (2 min) of a coumarin-labelled alkyne. Scale bar, 200 μm. (d) Fluorescence intensity profiles versus distance from the cathode visualizing the resulting dye gradient for different reaction times (raw data, obtained ex situ).
Mentions: A schematic representation of the second (CuAAC) reaction studied is shown in Fig. 4a, in which a [Cu(I)] gradient is applied on top of an azide-terminated silane layer that is attached to the glass substrate areas between the electrodes of an interdigitated electrode array. The Cu(I) catalyst is formed in situ by an one-electron reduction of already present Cu(II)36, at the cathode (source), whereas oxidation of the generated Cu(I) back to Cu(II) at the anode (sink) makes sure a stable gradient is formed. The solution gradient of [Cu(I)] is then exploited in the electrochemically activated CuAAC (‘e-click’) of an alkyne from solution to the azide monolayer resulting in a surface gradient. The reaction is monitored ex situ via immobilization of an alkyne-modified fluorescein onto the azide-terminated monolayer. The rate of this reaction is expected to be the highest close to the cathode, at which electrode the reduction of Cu(II) to Cu(I) is expected to occur.

Bottom Line: Because reaction kinetics is different at surfaces compared with solution, frequently, solution-characterization techniques cannot be used.For both systems, the kinetic data were spatially visualized in a two-dimensional reactivity map.In the case of the copper(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition, the reaction order (2) was deduced from it.

View Article: PubMed Central - PubMed

Affiliation: Molecular Nanofabrication Group, MESA+ Institute for Nanotechnology, University of Twente, PO Box 217, Enschede 7500 AE, The Netherlands.

ABSTRACT
Studying and controlling reactions at surfaces is of great fundamental and applied interest in, among others, biology, electronics and catalysis. Because reaction kinetics is different at surfaces compared with solution, frequently, solution-characterization techniques cannot be used. Here we report solution gradients, prepared by electrochemical means, for controlling and monitoring reactivity at surfaces in space and time. As a proof of principle, electrochemically derived gradients of a reaction parameter (pH) and of a catalyst (Cu(I)) have been employed to make surface gradients on the micron scale and to study the kinetics of the (surface-confined) imine hydrolysis and the copper(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition, respectively. For both systems, the kinetic data were spatially visualized in a two-dimensional reactivity map. In the case of the copper(I)-catalysed azide-alkyne 1,3-dipolar cycloaddition, the reaction order (2) was deduced from it.

No MeSH data available.