Olivier Felix

Charge-assisted N–H(+)···O(−) and O–H···O(−) hydrogen bonds control the supramolecular aggregation of ferrocenedicarboxylic acid and bis-amidines

Directional N–H···O and O–H···O hydrogen bonds reinforced by charge assistance in the presence of anion–cation interactions have been used to design and synthesise a whole family of new organic-organometallic supramolecular salts. The compounds [C5H16N4]2+[(η5-C5H4COO)2Fe]2−·2C2H5OH, 1, [C5H16N4]2+{[(η5-C5H4COOH)(η5-C5H4COO)Fe]2}2−, 2, [C7H20N4]2+[(η5-C5H4COO)2Fe]2−·4H2O, 3, [C7H20N4]2+{[(η5-C5H4COOH)(η5-C5H4COO)Fe]2}2−, 4, and [C7H18O2N4]2+[(η5-C5H4COO)2Fe]2− ·4H2O, 5, have been obtained by reacting [(η5-C5H4COOH)2Fe] with the bis-amidines [C5H14N4], [C7H18N4] and [C7H16O2N4]. The self-assembly between singly and doubly deprotonated acids and the protonated cations is controlled by the stoichiometric ratio and by the choice of solvent. The effect of charge assistance on the N–H···O interactions is discussed on the basis of a CSD analysis.

Layer-by-Layer Assembled Films Composed of “Charge Matched” and “Length Matched” Polysaccharides: Self-Patterning and Unexpected Effects of the Degree of Polymerization

The functionalization of chitosan with carboxymethyl groups allows zwitterionic or anionic chitosan derivatives to be obtained as a function of the degree of substitution. Here, we show that polyelectrolyte multilayers of chitosan and carboxymethylchitosan can be assembled by “dipping” or “spraying” to form strongly hydrated films in which both the polyanion and polycation possess the same polymer backbone (“matched chemistries”). Such films grow rapidly to fairly large thickness in very few assembly steps, especially in the case of “matched” charge densities, and atomic force microscopy reveals the formation of surface patterns that are dependent on the deposition conditions and on the number of layers. Interestingly, the influence of the molar masses of the polyelectrolyte pairs on the complex formation is somewhat counterintuitive, the stronger complexation occurring between polyanions and polycations of different (“non-matching”) lengths.

Bio-Inspired Multiproperty Materials: Strong, Self-Healing, and Transparent Artificial Wood Nanostructures

Nanocomposite films possessing multiple interesting properties (mechanical strength, optical transparency, self-healing, and partial biodegradability) are discussed. We used Layer-by-Layer assembly to prepare micron thick wood-inspired films from anionic nanofibrillated cellulose and cationic poly(vinyl amine). The film growth was carried out at different pH values to obtain films of different chemical composition, whereby, and as expected, higher pH values led to a higher polycation content and also to 6 times higher film growth increments (from 9 to 55 nm per layer pair). In the pH range from 8 to 11, micron thick and optically transparent LbL films are obtained by automated dipping when dried regularly in a stream of air. Films with a size of 10 cm(2) or more can be peeled from flat surfaces; they show tensile strengths up to about 250 MPa and Youngs moduli up to about 18 GPa as controlled by the polycation/polyanion ratio of the film. Experiments at different humidities revealed the plasticizing effect of water in the films and allowed reversible switching of their mechanical properties. Whereas dry films are strong and brittle (Youngs modulus: 16 GPa, strain at break: 1.7%), wet films are soft and ductile (Youngs modulus: 0.1 GPa, strain at break: 49%). Wet film surfaces even amalgamate upon contact to yield mechanically stable junctions. We attribute the switchability of the mechanical properties and the propensity for self-repair to changes in the polycation mobility that are brought about by the plastifying effect of water.

Molecular tectonics and supramolecular chirality: rational design of hybrid 1-D and 2-D H-bonded molecular networks based on bis-amidinium dication and metal cyanide anions

Using the bis-amidinium dication 1 bearing four acidic protons disposed in a divergent fashion and capable of chelating, through H-bonds, metal cyanide anions, neutral 1- and 2-D hybrid networks were generated. Whereas in the presence of M(CN)42− (M = Ni(II), Pd(II) and Pt(II)), 1-D H-bonded networks are formed through a double dihapto mode of H-bonding between the dication and the dianion, in the case of M(CN)64− (M = Fe(II) and Ru(II)), 2-D networks based on the interconnection by the dication 1 of 1-D networks analogous to those formed in the case of [M(CN)4]2− mentioned above are obtained. Interestingly, in the case of [M(CN)6]3− (M = Cr(III)), again a 2-D H-bonded network is formed through the formation of three dihapto modes of H-bonding between the dication and the trianion. Due to this dihapto or chelate mode of H-bonding, a supramolecular chirality of the Δ′ and Λ′ type is generated within the second coordination sphere of the metallic centres. The packing of the achiral 2-D networks thus obtained leads to channels which are occupied by water molecules forming polymeric H-bonded chains.

Nanoprotective Layer-by-Layer coatings with epoxy components for enhancing abrasion resistance: toward robust multimaterial nanoscale films.

Layer-by-Layer (LbL) assembled films offer many interesting applications (e.g., in the field of nanoplasmonics), but are often mechanically feeble. The preparation of nanoprotective films of an oligomeric novolac epoxy resin with poly(ethyleneimine) using covalent LbL-assembly is described. The film growth is linear, and the thickness increment per layer pair is easily controlled by varying the polymer concentration and/or the adsorption times. The abrasion resistance of such cross-linked films was tested using a conventional rubbing machine and found to be greatly enhanced in comparison to that of classic LbL-films that are mostly assembled through electrostatic interactions. These robust LbL-films are then used to mechanically protect LbL-films that would completely be removed by a few rubbing cycles in the absence of a protective coating. A 45 nm thick LbL-film composed of gold nanoparticles and poly(allylamine hydrochloride) was chosen as an especially weak example for a functional multilayer system. The critical thickness for the protective LbL-coatings on top of the weak multilayer was determined to be about 6 layer pairs corresponding to about only 10 nm. At this thickness, the whole film withstands at least 25 abrasion cycles with a reduction of the total thickness of only about 2%.

Altering the Static Dipole on Surfaces through Chemistry: Molecular Films of Zwitterionic Quinonoids

The adsorption of molecular films made of small molecules with a large intrinsic electrical dipole has been explored. The data indicate that such dipolar molecules may be used for altering the interface dipole screening at the metal electrode interface in organic electronics. More specifically, we have investigated the surface electronic spectroscopic properties of zwitterionic molecules containing 12π electrons of the p-benzoquinonemonoimine type, C(6)H(2)(···NHR)(2)(···O)(2)(R = H (1), n-C(4)H(9) (2), C(3)H(6)-S-CH(3) (3), C(3)H(6)-O-CH(3) (4), CH(2)-C(6)H(5) (5)), adsorbed on Au. These molecules are stable zwitterions by virtue of the meta positions occupied by the nitrogen and oxygen substituents on the central ring, respectively. The structures of 2-4 have been determined by single crystal X-ray diffraction and indicate that in these molecules, two chemically connected but electronically not conjugated 6π electron subunits are present, which explains their strong dipolar character. We systematically observed that homogeneous molecular films with thickness as small as 1 nm were formed on Au, which fully cover the surface, even for a variety of R substituents. Preferential adsorption toward the patterned gold areas on SiO(2) substrates was found with 4. Optimum self-assembling of 2 and 5 results in ordered close packed films, which exhibit n-type character, based on the position of the Fermi level close to the conduction band minimum, suggesting high conductivity properties. This new type of self-assembled molecular films offers interesting possibilities for engineering metal-organic interfaces, of critical importance for organic electronics.

Molecular tectonics V: Molecular recognition in the formation of molecular networks based on hydrogen bonding and electrostatic interactions

Abstract The formation of α-molecular networks based on dihapto mode of H-bonding was investigated in the solid state using bis-cyclic amidinium dications and acetylenedicarboxylate dianion. It has been demonstrated that the formation of networks depends strongly on the structure of the components. A proper disposition of H-bond donor and acceptor sites indeed leads to the formation of infinite molecular assemblies in the crystalline phase.

MOLECULAR TECTONICS IV : MOLECULAR NETWORKS BASED ON HYDROGEN BONDING AND ELECTROSTATIC INTERACTIONS

Whereas diprotonated 1 (1,2-Bis(2′-tetrahydropyrimidyl)ethane) forms a discrete exobinuclear complex with a dihapto mode of hydrogen bonding with 4-methylbenzoate anion 2 − in the solid state, with 4,4′-biphenyldicarboxylate 3 2− and α-network composed of 1-2H + dication and 3 2− dianion interconnected through strong hydrogen bonds and arranged in an alternating manner was obtained. The interconnection of the linear chains by water molecules affords a β-network.

Design of 2-D hydrogen bonded molecular networks using pyromellitate dianion and cyclic bisamidinium dication as complementary tectons

Using both H-bonding and ionic interactions, a dicationic tecton composed of two cyclic amidinium units and bearing four H-bond donor sites was self-assembled in the crystalline phase into a 2-D molecular networks in the presence of pyromellitate dianion.

Advanced fibroblast proliferation inhibition for biocompatible coating by electrostatic layer-by-layer assemblies of heparin and chitosan derivatives

Heparin and different chitosan derivatives were applied to produce stable electrostatic layer-by-layer assemblies and further used as coating technique to inhibit natural inflammatory response to implants. Heparin was assembled with chitosan and N-methylated chitosan derivatives, namely N,N-dimethyl chitosan (DMC) and N,N,N-trimethyl chitosan (TMC), by dipping method. DMC and TMC (chitosan derivatives) were synthesized and characterized before LbL assembly. Ellipsometry, quartz crystal microbalance (QCM-D), and contact angle were used to demonstrate the deposition of polyelectrolyte multilayers onto silicon wafers using polyelectrolyte solutions with different ionic strength. The biological properties of these films were evaluated by cell culture assays using NIH/3T3 fibroblast cells. LbL assemblies of Heparin and chitosan derivatives showed to be biocompatible, and at the same time they strongly hinder the proliferation speed of fibroblasts up to 40-fold factors. Therefore, the multilayers prepared from heparin and chitosan derivatives have good features to be used as an alternative coating treatment for biomedical implants with reduced body rejection properties.