Félix Busqué

Catechol-based biomimetic functional materials

Catechols are found in nature taking part in a remarkably broad scope of biochemical processes and functions. Though not exclusively, such versatility may be traced back to several properties uniquely found together in the o-dihydroxyaryl chemical function; namely, its ability to establish reversible equilibria at moderate redox potentials and pHs and to irreversibly cross-link through complex oxidation mechanisms; its excellent chelating properties, greatly exemplified by, but by no means exclusive, to the binding of Fe(3+); and the diverse modes of interaction of the vicinal hydroxyl groups with all kinds of surfaces of remarkably different chemical and physical nature. Thanks to this diversity, catechols can be found either as simple molecular systems, forming part of supramolacular structures, coordinated to different metal ions or as macromolecules mostly arising from polymerization mechanisms through covalent bonds. Such versatility has allowed catechols to participate in several natural processes and functions that range from the adhesive properties of marine organisms to the storage of some transition metal ions. As a result of such an astonishing range of functionalities, catechol-based systems have in recent years been subject to intense research, aimed at mimicking these natural systems in order to develop new functional materials and coatings. A comprehensive review of these studies is discussed in this paper.

Versatile Nanostructured Materials via Direct Reaction of Functionalized Catechols

A facile one-step polymerization strategy is explored to achieve novel catechol-based materials. Depending on the functionality of the catechol, the as-prepared product can be used to modify at will the surface tension of nano and bulk structures, from oleo-/hydrophobic to highly hydrophilic. A hydrophobic catechol prepared thus polymerized shows the ability to self-assemble as solid nanoparticles with sticky properties in polar solvent media. Such a versatile concept is ideal for the development of catechol-based multifunctional materials.

A Metal-Free General Procedure for Oxidation of Secondary Amines to Nitrones

An efficient and metal-free protocol for direct oxidation of secondary amines to nitrones has been developed, using Oxone in a biphasic basic medium as the sole oxidant. The method is general and tolerant with other functional groups or existing stereogenic centers, providing rapid access to enantiomerically pure compounds in good yields.

Two-Photon Neuronal and Astrocytic Stimulation with Azobenzene-Based Photoswitches

Synthetic photochromic compounds can be designed to control a variety of proteins and their biochemical functions in living cells, but the high spatiotemporal precision and tissue penetration of two-photon stimulation have never been investigated in these molecules. Here we demonstrate two-photon excitation of azobenzene-based protein switches and versatile strategies to enhance their photochemical responses. This enables new applications to control the activation of neurons and astrocytes with cellular and subcellular resolution.

Diastereoselective synthesis of allosecurinine and viroallosecurinine from menisdaurilide.

A new and versatile synthetic route to Securinega alkaloids is reported. The first synthesis of allosecurinine has been accomplished in seven steps and 40% yield, starting from (+)-menisdaurilide, using a vinylogous Mannich reaction as the key transformation. Similarly, viroallosecurinine has been synthesized from (-)-menisdaurilide.

Efficient synthesis of (S)-3,4-dihydro-2-pivaloyloxymethyl-2H-pyrrole 1-oxide

Abstract A convenient synthesis of the title nitrone is reported. The sequence starts from ethyl l -pyroglutamate as the source of chirality and the key step is the generation of an unstable α-methoxy- N -carboxylate ion, which readily decomposes to an imine. The oxidation of the imine with methyl(trifluoromethyl)dioxirane provides the enantiopure nitrone, which is trapped with dimethyl acetylenedicarboxylate.

Periodic mesoporous silica having covalently attached tris(bipyridine)ruthenium complex: synthesis, photovoltaic and electrochemiluminescent properties

A tris(bipyridine)ruthenium derivative with two terminal triethoxysilyl groups attached to one of the bipyridine ligands has been synthesized and used in combination with TEOS for the preparation of a tris(bipyridine)ruthenium-containing mesoporous silica, using CTABr as a structure-directing agent, under basic conditions at 100 °C. The resulting solids exhibited XRD patterns, isothermal gas adsorption and electron-microscopy images characteristic of hexagonal mesoporous silica, while the presence of tris(bipyridine)ruthenium complexes at the walls is manifested by the orange coloration of the solids and the optical spectra of the material corresponding to tris(bipyridine)ruthenium(II). The removal of the structure-directing agent without damaging the complex or the mesoporous structure of the pores was done by exhaustive solid–liquid extraction. As-synthesized mpRu exhibits photovoltaic (VOC = 140 mV, ISC = 2.6 µA) and electrochemiluminescence activity (λmax = 610 nm), the presence of CTABr plays a positive role in the activity by promoting intraparticle charge migration. In contrast, for an analogous material prepared under the same conditions but in the absence of the structure-directing agent and having a low surface area, the amorphous structure did not exhibit significant a photovoltaic or electrochemiluminescence response. This result exemplifies the benefits of having porosity and accessibility to the photoactive metallic complexes.

Mussel-Inspired Hydrophobic Coatings for Water-Repellent Textiles and Oil Removal

A series of catechol derivatives with a different number of linear alkyl chain substituents, and different length, have been shown to polymerize in the presence of aqueous ammonia and air, yielding hydrophobic coatings that present the ability to provide robust and efficient water repellency on weaved textiles, including hydrophilic cotton. The polymerization strategy presented exemplifies an alternative route to established melanin- and polydopamine-like functional coatings, affording designs in which all catechol (adhesive) moieties support specific functional side chains for maximization of the desired (hydrophobic) functionality. The coatings obtained proved effective in the transformation of polyester and cotton weaves, as well as filter paper, into reusable water-repellent, oil-absorbent materials capable of retaining roughly double their weight in model compounds (n-tetradecane and olive oil), as well as of separating water/oil mixtures by simple filtration.

Switchable self-assembly of a bioinspired alkyl catechol at a solid/liquid interface: competitive interfacial, noncovalent, and solvent interactions.

The large tendency of catechol rings to adsorb on surfaces has been studied by STM experiments with molecular resolution combined with molecular-dynamics simulations. The strong adhesion is due to interactions with the surface and solvent effects. Moreover, the thermodynamic control over the differential adsorption of 1 and the nonanoic solvent molecules has been used to induce a new temperature-induced switchable interconversion. Two different phases that differ in their crystal packing and the presence of solvent molecules coexist upon an increase or decrease in the temperature. These results open new insight into the behavior of catechol molecules on surfaces and 2D molecular suprastructures.

From p-benzoquinone to cyclohexane chirons: first asymmetric synthesis of (+)-rengyolone and (+)- and (−)-menisdaurilide

Abstract Starting from a common, easily available, enantiopure monoketal of p -benzoquinone, the synthesis of a large number of cyclohexane chirons has been achieved. The first synthesis of (+)-rengyolone and (+)- and (−)-menisdaurilide has been performed from one of these new building blocks. The wide variety of functional groups of this series of chirons makes them useful for subsequent synthetic processes.