Supramolecular chemistry | EPFL Graph Search

Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces, electrostatic charge, or hydrogen bonding to strong covalent bonding, provided that the electronic coupling strength remains small relative to the energy parameters of the component. While traditional chemistry concentrates on the covalent bond, supramolecular chemistry examines the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi–pi interactions and electrostatic effects. Important concepts advanced by supramolecular chemistry include molecular self-assembly, molecular folding, molecular recognition, host–guest chemistry, mechanically-interlocked molecular architectures, and dynamic covalent chemistry. The study of non-c

Mechanistic Insight into Supramolecular Polymerization in Water Tunable by Molecular Geometry

Lukas Pfeifer, Fan Xu

Supramolecular self-assembly in water based on non-covalent bonding is attracting major attention due to the potential of hydrogels and aqueous polymers in biomedical applications. Although supramolecular polymerization in organic solvents is well established, the key design features, the assembly mechanisms in water and achieving control over the aggregate structures remain challenging. Here, we present the assembly and disassembly of geometrical isomers of a stiff-stilbene bis-urea amphiphile (SA) in pure water. A remarkable feature of this system is that the (E)-isomer forms supramolecular polymers in both pure water and organic solvents. Taking advantage of this unique property, the hydrophobic effect was studied by comparing the supramolecular assembly in both systems. The assembly process in water follows an enthalpy-driven nucleation-elongation (cooperative) supramolecular polymerization mechanism with a standard Gibbs free energy (Delta G degrees = -53 kJ mol(-1)) double the value of the one found in toluene. We attributed this distinctive feature to the hydrophobic effect in water. Furthermore, we discovered an isomer-dependent assembly process, which can be used to control aggregation in aqueous media. Due to the substantial geometric difference between (E)-SA and (Z)-SA, we compared their assembly in water to study the influence of different driving forces involved in the process. The supramolecular polymerization of (E)-SA was cooperatively influenced by hydrogen bonding, pi-stacking, and hydrophobic effects, whereas the assembly of (Z)-SA was mainly driven by hydrophobic effects. As a result, the fiber length of (E)-SA in water is much longer than that of (Z)-SA, presenting opportunities for geometrical control of aggregation in aqueous media. [GRAPHICS]

CHINESE CHEMICAL SOC2022

Enantiopure helical (supra)molecular arrays containing lanthanides

Marco Antonio Lama

The diastereoselective synthesis of chiral coordination compounds with d metals proved the effectiveness of the pinene-bipyridine approach in predetermining the chirality at the metal centre. The strong Lewis acidic character of lanthanide cations required the modification of this class of ligands in order to adapt their coordination properties to the binding affinity of Ln(III) toward hard donor atoms like oxygen. The pinene bipyridine carboxylic derivative (+)-L- (figure 1) has been designed and synthesized to form configurationally stable lanthanide complexes. This ligand proved its effectiveness as chiral building block for the synthesis of oligometallic supramolecular structures. Indeed a self-assembly process takes place with complete diastereoselectivity between the enantiomerically pure (-) or (+) L- and Ln(III) ions (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) in methanol, giving rise to trinuclear enantiopure structures with general formula Ln3(L)6(µ3-OH)(H2O)32 , possessing predetermined helical chirality. The ligands in this case display a new version of supramolecular helical chirality since they are wrapping around a trimetallic core instead of one single metal centre. The same components afford a second polynuclear structure if the reaction is carried out in CH3CN. In this medium a three-dimensional tetranuclear array self-assembles (with general formula Ln4(L)9(µ3-OH)2). The nine ligands are forming three distinct helical domains, two supramolecular as in the case of the trinuclear array and one classical around a single metal centre, with predetermined configuration. The two classes of compounds have been structurally characterized in solid state (X-ray and IR) and in solution (ES-MS, NMR). Their chiroptical properties were investigated by means of Circular Dichroism and Circularly Polarized Luminescence (for the emitting compounds). Trinuclear and tetranuclear arrays are shown to interconvert in CH3CN, in a process mediated by water. This process was rationalized taking into account the nature of the Ln(III) ions, the initial concentration of the components and the addition or removal of water in solution. The availability of both the enantiomers of the ligand prompted us to study the self-recognition capabilities of the two systems. 1H-NMR and CD studies reveal an almost complete chiral recognition in the self-assembly leading to the trinuclear complex. The process leading to tetranuclear species appears instead perturbed, probably due to the higher number of fundamental components involved (4 metals and 9 ligands instead of 3 metals and 6 ligands). Figure 1: Reaction conditions leading to the synthesis of trinuclear and tetranuclear Ln(III) complexes with ligand (+)-L-. The introduction of a carboxylic moiety onto the 6' posititon of the (-)-5,6- and (-)-4,5- pinene bipyridine lead to the tridentate ligands (-)-HL1 and (-)-HL2, respectively. Mononuclear neutral complexes are obtained upon reaction with Ln(ClO4)3. Different extents of diastereoselectivity are pointed out in the two systems by X-ray analysis and CD spectroscopy. In particular the ligand (-)-HL1, in which the pinene moiety is next to the binding site, seems to be more effective in predetermining the configuration at the metal centre. A low diastereoselectivity is instead expressed in the reactions with (-)-HL2 as revealed by the X-ray structure of [Pr{(-)-L2}3] (both Δ and Λ isomers detected) and by the CD spectrum void of signal.

EPFL2006

Reversible supramolecular modification of surfaces

Negar Moridi

Enzymes are biocatalysts widely used in a large number of industrial biotech processes as they offer clear advantages over their chemical counterparts. Indeed, enzymes often show high substrate selectivity along with elevated turnover rates. Enzymatic catalysis usually functions under mild conditions of temperature, pressure and acidity. However, the industrial application of enzymes is often limited by their limited stability under operational conditions. Moreover, due to high water solubility of enzymes it is challenging to confined them in a flow reactor system. In order to circumvent these limitations, we have developed a supramolecular strategy that allows the reversible immobilization of active enzyme-polymer conjugates at the surface of filtration membranes. It is based on multivalent host-guest inclusion interactions between the membrane surface and a soluble enzyme-polymer conjugate. Cyclodextrins (CDs) as "host" molecules are covalently attached at the surface of polyethersulfone membranes and a multivalent water-soluble polymer is synthesized as a "guest" molecule. We demonstrate that while this supramolecular surface modification is stable under operational conditions and allows for efficient bio-catalysis, it can be straightforwardly reverse by competitive host-guest interactions. The first part of this manuscript is dedicated to a literature review on selected topics. As the supramolecular strategy we have developed in the course of this PhD research work is based on the use of cyclodextrins as supramolecular host molecules, the first part of this literature review focuses on the physico-chemical characteristics of this class of macrocycles. A special emphasis is done on their ability to form host-guest multivalent inclusion complexes. In this context, we describe the concept of multivalency and the underpinning essential thermodynamic principles, which can be apply to design controllable, directional, and selective self-assemblies. In the second part of this manuscript, we present our strategy to bio-functionalize polymeric membrane surfaces using multivalent reversible inclusion reactions. In more details, the chemical strategy to introduce CD macrocycles, in a covalent fashion, at the surface of the polymeric material is discussed. The synthesis and characterization of an enzyme-polymer conjugate, possessing multiple chemical functional groups (i.e. adamantyl) able to form inclusion complexes with CDs, is presented. It is demonstrated that this supramolecular strategy could be applied to the reversible immobilization of an active enzyme at the surface of polyethersulfone membranes. A similar strategy is applied to the reversible bio-functionalization of gold surfaces and used to prepare sensor chips for surface plasmon resonance (SPR) experiments. Self-assembled monolayers of CDs derivatives are prepared on the surface of a gold sensor chip. A water-soluble protein-polymer conjugate, possessing multiple adamantyl moieties, is synthesized. The supramolecular reversible binding of this new conjugate on the chemically modified SPR chip is demonstrated. The possibility to use this system for antigen/antibody biosensing experiment is successfully confirmed.

EPFL2015