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A molecular interface science approach: Decoding single molecular reactions and interactions at dynamic solid/liquid interfaces

Periodic Reporting for period 4 - CSI.interface (A molecular interface science approach: Decoding single molecular reactions and interactions at dynamic solid/liquid interfaces)

Reporting period: 2020-10-01 to 2021-06-30

Generating a detailed molecular understanding of complex, simultaneous interactions at reactive/dynamic solid/fluid interfaces is one of the biggest contemporary scientific challenges across disciplines. Whether it is during corrosive coating degradation, in biological adhesion, or during adaptive interfacial redox-cycle feedback in strongly adhesive seawater organisms: It is a large numbers of similar or dissimilar molecule/molecule, molecule/surface and competing interactions with ions/water that mediate complex macroscopic properties at crowded solid/liquid interfaces. How do single molecular interactions at dynamic, reactive or steady state interfaces translate into a macroscopically observable outcome?
After decades of truly transformative advancements in single molecule (bio)physics and surface science, it is still no more than a vision to predict and control macroscopic phenomena such as adhesion or electrochemical reaction rates at solid/liquid interfaces based on well-characterized single molecular interactions. How exactly do inherently dynamic and simultaneous interactions of a countless number of interacting “crowded” molecules lead to a concerted outcome/property at the macroscopic scale?
In CSI.interface we unraveled the scaling of single molecule interactions towards macroscopic properties at adhesive and redox-active solid/liquid interfaces. Combining Atomic Force Microscopy (AFM) based single molecule force spectroscopy and macroscopic Surface Forces Apparatus (SFA) experiments CSI.interface

(1) derived rules for describing complex chemically diverse adhesive solid/liquid interfaces, and
(2) we build a novel apparatus in order to measure single-molecule steady-state dynamics of both redox cycles as well as binding unbinding cycles of specific interactions, and how these react to environmental triggers.

With this, CSI.interface went well beyond present applications of AFM and SFA and has the long-term potential to revolutionize our understanding of interfacial interaction under steady state, responsive and dynamic conditions. This work paved the road for knowledge-based designing of next-generation technologies in gluing, coating, bio-adhesion, materials design and much beyond. Specifically, applications of this fundamental research can range from propelling the development of novel medical adhesives, to understanding delamination and corrosion protection by coatings in automotive and aviation industry, or materials design for electrochemical reactivity and transformation of materials. A spin of company for commercializing the newly designed unique apparatus and other transformative new technology is anticipated based on a patent submitted as a result of this action. This will boost competitiveness and innovation leadership of Europe.
The work performed was organized around the two major objectives, which are (1) to provide a general scheme for predicting macroscopic properties such as adhesion and redox/reactivity at crowded solid/liquid interfaces, including understanding the scaling of nonlinearities from the single molecular to the macroscopic scale. The aim is to ultimately derive macroscopic properties directly from single molecule measurements together with a comprehensive scaling approach, i.e. and understanding of time and dimensionality of a system emerging from molecular units (Objective 1), and to (2) setup a novel scientific equipment – the Molecular Forces Apparatus (MFA) – that will transform how we can measure and manipulate molecules at dynamic/ reactive solid/liquid interfaces, and in particular under steady state conditions. This will allow to “feel” a steady state condition and how it reacts to environmental triggers. (Objective 2).
Objective 1 was achieved, and we are now able to provide a general scheme for predicting macroscopic properties such as adhesion and redox/reactivity at crowded solid/liquid interfaces, based on a kinetic model of competing Langmuir isotherms. We could also show that the macroscopic model can be verified by single molecule measurements with the AFM (to be published). We are now able to further understand time effects and dimensionality (local effects) of a system emerging from molecular units.
Objective 2 as achieved: We did setup a novel scientific equipment – the Molecular Forces Apparatus (MFA) – that can measure force versus distance profiles at constant distances, which are fully feedback controlled in 5 dimensions. A patent was submitted and a potential spin-off is anticipated as direct outcome of this action.
This project achieved a number of major results beyond state of the art, and we were able to develop and commercialize a new software code for analysis of multiple beam interferometry in reflection mode.

1. We could progress from a proof-of principle, towards a working new instrument called the Molecular Forces Apparatus (MFA). With the MFA we can now uniquely demonstrate that we can stabilize the position of two interacting bodies in a force probe experiment to within 8-10 Angstroms in all three spatial dimensions. This is a unique advance, that will allow us now to perform hitherto impossible force probe experiments, with constant distance. As continuing effort we will now enable measuring of single molecular interactions at constant distance at solid/liquid interfaces. The MFA, which we constructed for this unique experiment is at this point in time in the active research state, we performed extensive test force probe experiments. These possibilities are absolutely new and beyond state of the art, as there is currently no other equipment that can perform a similar experiment. As anticipated the developed equipment and software will be the basis for founding a highly competitive and cutting-edge spin-off company with a unique portfolio after the conclusion of this project (based on the submitted patent).
2. Using a newly developed ultra stable model system we were able to unravel competitive effects and scaling effects of adhesive bonding in an aqueous environment. The advances made, allow us now to describe complexity at the molecular scale for predicting macroscopic properties based on single molecular events. For the first time it is now possible to predict a complex situation at a solid liquid interface – based on single molecular data and interaction free energies as they can be measured by experiment. With this result a completely new approach – a molecular interface science – became possible though this action.
3. By now we progressed to a new understanding of the catechol functionality on L-DOPA. Specifically, we can show that this functionality triggers a number of hitherto unexpected side reactions. We have found a surprisingly simple way how these side reactions can be controlled. This opens up the possibility to implement mussel glue principles into technical polymers with full control of the electrochemistry, opening new paths towards wet adhesives with superior performance.
4. A new software analysis tool for white light interferometry, the SFAexplorer, was developed, tested and commercialized in this project. By now, this new tool is licensed by 4 international research institutions spread across the world (Asia, Canada, USA, Europe).
This image shows how molecules stretch and adapt during the breaking of a molecular contact.