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Carbohydrate self-assembly at metal surfaces

by PREVOTS Evelyne - published on , updated on

Saccharides are ubiquitous biomolecules, but little is known about their interactions with surfaces, and about their conformations and 2D self-assembly. By combining soft-landing electrospray ion beam deposition, scanning tunneling microscopy imaging and multi‐stage modelling, the conformation and assembly patterns on Cu(100) of two disaccharides, sucrose and trehalose, were revealed.

Saccharides, also known as carbohydrates, are ubiquitous biomolecules, but little is known about their interaction with surfaces. Soft-landing electrospray ion beam deposition in conjunction with high-resolution imaging by scanning tunneling microscopy (STM) now provides access to the molecular details of the surface assembly of this important class of biomolecules. As examples, sucrose - one of the most widely used ingredients in the food industry - and trehalose that exhibits strong effects on the anhydrobiosis of biosystems, were chosen for the study of their self-assembly on a Cu(100) surface. Sucrose molecules were found to be mobile at room temperature (RT) but after cooling to 40 K nearly all the molecules are assembled in 2D islands in form of periodic networks. In contrast, trehalose molecules already self-assemble at RT, and a variety of combinations of at least two basic compatible structural motifs is observed (a linear chain and a 8-molecule hollow square block). To shed light on the molecular conformations and their assemblies, a multi-stage modelling procedure was employed. It was composed of global explorations of the potential energy landscapes using a new algorithm called IGLOO (a stochastic method that performs global optimization by iterating local searches) followed by DFT refinements, yielding energetically nearly equivalent conformations representing different possibilities for the disaccharides to adsorb on the surface. Applying the constraints of the STM observations, we rationalized which conformation is the observed one for each molecule, and constructed models for the intermolecular interactions. The specific knowledge gained about their adsorption geometry can help in understanding the influence of these saccharides on e.g. hydration/anhydrobiosis properties. At this resolution, the combination of STM with state-of-the-art multi-stage simulation methods is a very promising approach to characterize the structure of complex carbohydrates adsorbed on surfaces, such as those involved in the formation of bacterial biofilms. This highlight reports a joint research work of CEMES, LAAS and MPI Stuttgart.

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1) STM image of the sucrose periodic network on Cu(100) at 40K. 2) Comparison of measured (left) with simulated STM images (center) and the molecular structures (right) of sucrose. 3) STM image of trehalose assembly on Cu(100) at RT. 4) Measured (left) and simulated (right) STM images of motif B partly overlaid with the molecular structure.

 

References

"Carbohydrate self-assembly at surfaces : STM imaging of sucrose conformation and ordering on Cu(100)" 
S. Abb, N. Tarrat, J. Cortés, B. Andriyevsky, L. Harnau, J. C. Schön, S. Rauschenbach, K. Kern
Angewandte Chemie Int. Ed., 2019, 58, 1. Back Cover !

"Polymorphism in carbohydrate self-assembly at surfaces : STM imaging and theoretical modeling of trehalose on Cu(100)"
S. Abb, N. Tarrat, J. Cortés, B. Andriyevsky, L. Harnau, J. C. Schön, S. Rauschenbach and K. Kern
RSC Advances, 2019, 9, 35813 – 35819.

 

Contact

Dr. Nathalie Tarrat