A Biocatalytic Nanomaterial for the Label-Free Detection of Virus-Like Particles.

The design of nanomaterials that are capable of specific and sensitive biomolecular recognition is an on-going challenge in the chemical and biochemical sciences. A number of sophisticated artificial systems have been designed to specifically recognize a variety of targets. However, methods based on natural biomolecular detection systems using antibodies are often superior. Besides greater affinity and selectivity, antibodies can be easily coupled to enzymatic systems that act as signal amplifiers, thus permitting impressively low detection limits. The possibility to translate this concept to artificial recognition systems remains limited due to design incompatibilities. Here we describe the synthesis of a synthetic nanomaterial capable of specific biomolecular detection by using an internal biocatalytic colorimetric detection and amplification system. The design of this nanomaterial relies on the ability to accurately grow hybrid protein-organosilica layers at the surface of silica nanoparticles. The method allows for label-free detection and quantification of targets at picomolar concentrations.

Enzyme Shielding in an Enzyme-thin and Soft Organosilica Layer.

The fragile nature of most enzymes is a major hindrance to their use in industrial processes. Herein, we describe a synthetic chemical strategy to produce hybrid organic/inorganic nanobiocatalysts; it exploits the self-assembly of silane building blocks at the surface of enzymes to grow an organosilica layer, of controlled thickness, that fully shields the enzyme. Remarkably, the enzyme triggers a rearrangement of this organosilica layer into a significantly soft structure. We demonstrate that this change in stiffness correlates with the biocatalytic turnover rate, and that the organosilica layer shields the enzyme in a soft environment with a markedly enhanced resistance to denaturing stresses.

Reversible Supramolecular Surface Attachment of Enzyme-Polymer Conjugates for the Design of Biocatalytic Filtration Membranes.

To be used successfully in continuous reactor systems, enzymes must either be retained using filtration membranes or immobilized on a solid component of the reactor. Whereas the first approach requires large amounts of energy, the second approach is limited by the low temporal stability of enzymes under operational conditions. To circumvent these major stumbling blocks, we have developed a strategy that enables the reversible supramolecular immobilization of bioactive enzyme-polymer conjugates at the surface of filtration membranes. The polymer is produced through a reversible addition-fragmentation transfer method; it contains multiple adamantyl moieties that are used to bind the resulting conjugate at the surface of the membrane which has surface-immobilized cyclodextrin macrocycles. This supramolecular modification is stable under operational conditions and allows for efficient biocatalysis, and can be reversed by competitive host-guest interactions.

Sequence-specific DNA interactions with calixarene-based langmuir monolayers.

The interactions of an amphiphilic calixarene, namely p-guanidino-dodecyloxy-calix[4]arene, 1, self-assembled as Langmuir monolayers, with short double stranded DNA, were investigated by surface pressure-area (π-A) isotherms, surface ellipsometry and Brewster angle microscopy (BAM). Three DNA 30mers were used as models, poly(AT), poly(GC) and a random DNA sequence with 50% of G:C base pairs. The interactions of these model DNA duplexes with 1-based Langmuir monolayers were studied by measuring compression isotherms using increasing DNA concentrations (10(-6), 10(-5), 10(-4), and 5 × 10(-4) g L(-1)) in the aqueous subphase. The isotherms of 1 showed an expansion of the monolayer with, interestingly, significant differences depending on the duplex DNA sequence studied. Indeed, the interactions of 1-based monolayers with poly(AT) led to an expansion of the monolayer that was significantly more pronounced that for monolayers on subphases of poly(GC) and the random DNA sequence. The structure and thickness of 1-based Langmuir monolayers were investigated by BAM and surface ellipsometry that showed differences in thickness and structure between a monolayer formed on pure water or on a DNA subphase, with here again relevant dissimilarities depending on the DNA composition.

Polymorphism control of an active pharmaceutical ingredient beneath calixarene-based Langmuir monolayers.

This communication demonstrates the possibility to nucleate and grow different crystalline polymorphic forms of gabapentin (GBP) using, as nucleation templates, Langmuir monolayers of an amphiphilic calixarene at different packing densities.

Langmuir-Blodgett monolayer stabilization using supramolecular clips.

We introduce the concept of stabilization of Langmuir-Blodgett (LB) films using dicarboxylate supramolecular clips, as demonstrated by Langmuir isotherms, spectroscopic ellipsometry, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurements.

Monolayers of an amphiphilic para-carboxy-calix[4]arene act as templates for the crystallization of acetaminophen.

The title compound, 5,11,17,23-tetra-carboxy-25,26,27,28-tetradodecyloxy-calix[4]arene, 1, has been studied at the air-water interface, self-assembled as Langmuir monolayers, for its ability to interact with an active pharmaceutical ingredient (API), acetaminophen (APAP), and to initiate its crystallization. The Π/A isotherm study shows that there is a clear interaction between 1 and APAP causing an expansion of the monolayer. In addition to the known phase transition occurring at a surface tension of 38 mN m(-1), an additional kink is observed in the compression isotherm for concentrations of APAP above 40 mM suggesting that this API is causing an additional phase transition of the monolayer. Interface-initiated crystallization studies show that the presence of a monolayer spread on a supersaturated solution of APAP (26 g L(-1)) triggers this API crystal growth from the interface. The transfer of 1-based monolayers on glass surfaces has been carried out using the Langmuir-Blodgett technique. The so-produced monolayers have been shown to template the crystallization of APAP. LB films of 1 have characterized using imaging and spectroscopic ellipsometry. The results suggest that each monolayer has an average thickness of 18 Å, which is consistent with the molecular structure of 1 self-organized parallel to the interface with the alkyl chains pointing out parallel to the axis of the macrocycle and without interdigitation of the alkyl chains. The presence of APAP in the subphase during the LB transfer causes a limited but relevant increase in the layer thickness. The study of the capabilities of the LB films to initiate crystallization of APAP is also demonstrated showing the influence of the monolayer packing on the quantity of formed crystals.

Resorcinarene bis-crown silver complexes and their application as antibacterial Langmuir-Blodgett films.

Silver complexes of a cation binding supramolecular host, resorcinarene bis-crown (CNBC5) with propyl, nonyl, decyl and undecyl alkyl chains were investigated by NMR titration, picrate extraction and single crystal X-ray diffraction. Binding studies showed that both 1 : 1 and 1 : 2 (host-Ag(+)) complexes are present in solution with only a slight effect of the lower rim alkyl chain length on the binding constants (log K 4.0-4.2 for 1 : 2 complexes). Solid state complexes of the resorcinarene bis-crowns bearing either C(3) or C(11) chains were obtained. Single crystal X-ray analyses showed that both derivatives bind silver ions by metal-arene and Ag···O coordination from the crown ether bridges and from the solvent, and pack in layered or bilayered fashion. Furthermore, the amphiphilic nature of C11BC5 was demonstrated using the Langmuir balance technique. Langmuir-Blodgett films of the amphiphilic C11BC5-Ag complex were transferred onto a substrate and shown to possess antibacterial activity against E. coli.

Amidophenol-modified amphiphilic calixarenes: synthesis, interfacial self-assembly, and acetaminophen crystal nucleation properties.

Three amidophenol-modified calixarenes have been produced reacting the parent 5,11,17,23-tetracarboxy-25,26,27,28-tetradodecyloxycalix[4]arene with o-, m-, and p-aminophenol. The produced amphiphiles have been shown to form stable monomolecular Langmuir layers on water. Working on subphases containing 1 mM acetaminophen (APAP), it has been demonstrated that the produced amphiphiles interact with this active pharmaceutically ingredient (API) with a relevant preference for the para-derivative that possesses in its structure substituents that are analogous to the target. Working at supersaturating concentrations of APAP, it has been demonstrated that the so-produced calixarene Langmuir monolayers do favor crystallization of APAP (polymorph I), with a clear effect of the packing density of the amphiphile at the interface on the quantity of produced crystals. Monolayers of the para-derivative have been transferred on solid substrates using the Langmuir-Blodgett technique; the so-produced ultrathin films have been shown to initiate surface crystal nucleation of APAP. The produced solids have been analyzed by single-crystal X-ray crystallography and shown to preferentially grow in the [010] direction.