Molecular Decoration of Ceramic Supports for Highly Effective Enzyme Immobilization-Material Approach

A highly effective method was developed to functionalize ceramic supports (Al₂O₃ powders and membranes) using newly synthesized spacer molecules. The functionalized materials were subsequently utilized for Candida antarctica lipase B enzyme immobilization. The objective is to systematically evaluate the impact of various spacer molecules grafted onto the alumina materials will affect both the immobilization of the enzymes and specific material surface properties, critical to enzymatic reactors performance. The enzyme loading was significantly improved for the supports modified with shorter spacer molecules, which possessed higher grafting effectiveness on the order of 90%. The specific enzyme activity was found to be much higher for samples functionalized with longer modifiers yielding excellent enantioselectivity >97%. However, the enantiomeric ratio of the immobilized lipase was slightly lower in the case of shorter spacer molecules.

Selective Proton-Mediated Transport by Electrogenic K+-Binding Macrocycles

Synthetic K+-binding macrocycles have potential as therapeutic agents for diseases associated with KcsA K+ channel dysfunction. We recently discovered that artificial self-assembled n-alkyl-benzoureido-15-crown-5-ether form selective ion-channels for K+ cations, which are highly preferred to Na+ cations. Here, we describe an impressive selective activation of the K+ transport via electrogenic macrocycles, stimulated by the addition of the carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP) proton carrier. The transport performances show that both the position of branching or the size of appended alkyl arms favor high transport activity and selectivity SK+/Na+ up to 48.8, one of the best values reported up to now. Our study demonstrates that high K+/Na+ selectivity obtained with natural KcsA K+ channels is achievable using simpler artificial macrocycles displaying constitutional functions.

Encapsulation versus Self-Aggregation toward Highly Selective Artificial K+ Channels

Natural ion-channel proteins allow ion transport across cell membranes at rates very close to those for ionic diffusion in water. Among them, natural KcsA K⁺ channels present high transport rates and total selectivity for K⁺ cations, rejecting all other cations. Most of the reported artificial ion channels cannot reach this type of activity because of their low selectivity. Several synthetic channels have been designed to mimic the natural KcSA channels, but those presenting an important K⁺/Na⁺ selectivity are limited. High-selectivity issues are determinant for the performance of natural protein channels, but they have been not considered as determinant in controlling the transport activity of the artificial ion channels. This Account discusses the last developments of artificial supramolecular carriers or channels that selectively transport K⁺ cations against other cations. Mimicking the complex structures of protein channels is an important research area. These studies are related to such adaptive biomimetic systems that can self-select their functions, with a specific emphasis on artificial superstructures enabling K⁺ transport like in the natural ones. Alternatively, it is more than interesting to synthetically construct only the active key structures of protein filters or gates that give the chemical selectivity or lead us to describe their dynamic role in the ion pumping and translocation along the channel. Several self-assembled macrocyclic channels are presented here. The macrocyclic binding sites may selectively encapsulate the K⁺ cations or form aggregated H-bonded central pores of self-assembled macrocycles that coordinate the K⁺ cations as hydrating water molecules in aqueous solution, compensating for the energetic cost of cation dehydration. These macrocyclic channels are responsive in the presence of K⁺ cations, even when a large excess of Na⁺ is present. From the mechanistic point of view, these systems express a synergistic dynamic feature: addition of K⁺ cations drives the selection and emergence of specific ion channels that selectively conduct the K⁺ cations that promoted the formation of channel superstructures in the first place. These highly permeable and K⁺-selective artificial channels may be considered as simple primitive biomimetic alternatives of natural KcsA channels that may find interesting applications in chemical separations, selective sensing, and biomedical materials.

G-Quartet hydrogels for effective cell growth applications

Functional G-quartet hydrogels formed from natural guanosine cross linked with benzene-1,4-diboronic acid and Mg²⁺ support cell growth with no visible signs of gel degradation.

Self-assembly of supramolecular triarylamine nanowires in mesoporous silica and biocompatible electrodes thereof

Biocompatible silica-based mesoporous materials, which present high surface areas combined with uniform distribution of nanopores, can be organized in functional nanopatterns for a number of applications. However, silica is by essence an electrically insulating material which precludes applications for electro-chemical devices. The formation of hybrid electroactive silica nanostructures is thus expected to be of great interest for the design of biocompatible conducting materials such as bioelectrodes. Here we show that we can grow supramolecular stacks of triarylamine molecules in the confined space of oriented mesopores of a silica nanolayer covering a gold electrode. This addressable bottom-up construction is triggered from solution simply by light irradiation. The resulting self-assembled nanowires act as highly conducting electronic pathways crossing the silica layer. They allow very efficient charge transfer from the redox species in solution to the gold surface. We demonstrate the potential of these hybrid constitutional materials by implementing them as biocathodes and by measuring laccase activity that reduces dioxygen to produce water.

Transcription of G-quartet supramolecular aggregates into hierarchical mesoporous silica nanotubes

Hierarchical porous silica nanotubes or porous silica hollow spheres were prepared employing a low concentration of G-quartet supramolecular aggregates as a template.

Highly Selective Artificial K(+) Channels: An Example of Selectivity-Induced Transmembrane Potential

Natural KcsA K(+) channels conduct at high rates with an extraordinary selectivity for K(+) cations, excluding the Na(+) or other cations. Biomimetic artificial channels have been designed in order to mimick the ionic activity of KcSA channels, but simple artificial systems presenting high K(+)/Na(+) selectivity are rare. Here we report an artificial ion channel of H-bonded hexyl-benzoureido-15-crown-5-ether, where K(+) cations are highly preferred to Na(+) cations. The K(+)-channel conductance is interpreted as arising in the formation of oligomeric highly cooperative channels, resulting in the cation-induced membrane polarization and enhanced transport rates without or under pH-active gradient. These channels are selectively responsive to the presence of K(+) cations, even in the presence of a large excess of Na(+). From the conceptual point of view, these channels express a synergistic adaptive behavior: the addition of the K(+) cation drives the selection and the construction of constitutional polarized ion channels toward the selective conduction of the K(+) cation that promotes their generation in the first place.

Host-guest chemistry of mesoporous silicas: precise design of location, density and orientation of molecular guests in mesopores

Mesoporous solids, which were prepared from inorganic-surfactant mesostructured materials, have been investigated due to their very large surface area and high porosity, pore size uniformity and variation, periodic pore arrangement and possible pore surface modification. Morphosyntheses from macroscopic morphologies such as bulk monolith and films, to nanoscopic ones, nanoparticles and their stable suspension, make mesoporous materials more attractive for applications and detailed characterization. This class of materials has been studied for such applications as adsorbents and catalysts, and later on, for optical, electronic, environmental and bio-related ones. This review summarizes the studies on the chemistry of mesoporous silica and functional guest species (host-guest chemistry) to highlight the present status and future applications of the host-guest hybrids.

Dynameric asymmetric membranes for directional water transport

Hydrophilic/hydrophobic dynamers prepared via template partial phase segregation have been used in the formation of asymmetric membranes for directional water transport.

Ion-specific self-assembly of a lipophilic guanosine derivative in thin surface films

We investigated the effect of various ions on the surface assembly of a guanosine derivative with one hexadecanoyl chain at the air-water interface. The ions were added to the water subphase prior to spreading of the surface film. Like in bulk water, also at the air-water interface, K(+) ions exhibit the strongest influence on the assembly features as they induce structural transformation from lamellar to mosaic-like assembly. In contrast, Li(+) and Na(+) ions only slightly modify the properties of the assembled film with respect to those observed on pure water. The nature of anions plays an important role in the surface self-assembly as well. We found that (Pic(-)) is 2 orders of magnitude more effective for assembly regulation than Cl(-). All surface assemblies observed in our study are very stable and robust, and consequently they remain practically unperturbed after Langmuir-Blodgett transfer onto a solid support.

Adaptive binding and selection of compressed 1,ω-diammonium-alkanes via molecular encapsulation in water

Guest molecules confined inside hollow molecular assemblies and thus protected from their environment can show unexpected structural behavior or special reactivity compared to their behavior in a bulk, unprotected environment. A special case is the coiling behavior of variable-length alkane chains in rigid hydrogen-bonded molecular cages. It has been found before that coiling may occur in such circumstances, but no experimental evidence concerning the exact conformation of the chains has yet been presented. We reveal in this study the self-assembly of a molecular cage in water and the crystalline state from three distinct components in which linear 1,ω-diammonium-alkanes chains are confined with different degrees of compression. The exact coiling behavior is determined from atomic resolution X-ray diffraction showing crenel-like conformations in the compressed state. Chemical selection can be obtained from mixtures of alkane chains via the encapsulation of kinetically stable conformations observed during the encapsulation of pure components. Moreover, it was found that uncompressed and compressed chains can be competitively trapped inside the capsule. These findings may provide insight in areas to a better understanding of biological processes, such as the fatty acid metabolism.

Selective recognition and extraction of KBr via cooperative interactions with a urea functionalized crown ether dual-host

Selective solid–liquid extraction of KBr is demonstrated for the first time with a crown ether based pentafluorophenyl urea functionalised dual-host receptor.

Core-shell inversion by pH modulation in dynamic covalent micelles

Dynamic covalent surfactants have been obtained by the reversible condensation of a hydrophobic aldehyde (ended by an ionic tip) with various neutral polyethylene glycol based hydrophilic amines. In water, the duality between the two hydrophilic domains (charged and neutral) leads to their segregation when the surfactants are self-assembled within micelles. Depending on the number of polyethylene glycol units, a core-shell inversion leading to a switching orientation of the ionic tips from the inside to the outside of the micelles has been demonstrated by a combination of scattering techniques. In competition experiments, when several amines of different pKas and hydrophilic polyethylene glycol chains are competing for the same aldehyde, it becomes possible to trigger this core-shell inversion by pH modulation and associated dynamic constitutional reorganization.

Ordered hybrids from template-free organosilane self-assembly

Despite considerable achievements over the last two decades, nonporous organic-inorganic hybrid materials are mostly amorphous, especially in the absence of solvothermal processes. The organosilane self-assembly approach is one of the few opportunities for creating a regular assembly of organic and inorganic moieties. Additionally, well-established organosilicon chemistry enables the introduction of numerous organic functionalities. The synthesis of periodically ordered hybrids relies on mono-, bis-, or multisilylated organosilane building blocks self-assembling into hybrid mesostructures or superstructures, subsequently cross-linked by siloxane Si-O-Si condensation. The general synthesis procedure is template-free and one-step. However, three concurrent processes underlie the generation of self-organized hybrid networks: thermodynamics of amphiphilic aggregation, dynamic self-assembly, and kinetically controlled sol-gel chemistry. Hence, the set of experimental conditions and the precursor structure are of paramount importance in achieving long-range order. Since the first developments in the mid-1990s, the subject has seen considerable progress leading to many innovative advanced nanomaterials providing promising applications in membranes, pollutant remediation, catalysis, conductive coatings, and optoelectronics. This work reviews, comprehensively, the primary evolution of this expanding field of research.

Self-sorting of dynamic metallosupramolecular libraries (DMLs) via metal-driven selection

“Metal-driven” selection between finite mononuclear and polymeric metallosupramolecular species can be quantitatively achieved.

Identifying guanosine self assembly at natural isotopic abundance by high-resolution 1H and 13C solid-state NMR spectroscopy

By means of the (1)H chemical shifts and the proton-proton proximities as identified in (1)H double-quantum (DQ) combined rotation and multiple-pulse spectroscopy (CRAMPS) solid-state NMR correlation spectra, ribbon-like and quartet-like self-assembly can be identified for guanosine derivatives without isotopic labeling for which it was not possible to obtain single crystals suitable for diffraction. Specifically, characteristic spectral fingerprints are observed for dG(C10)(2) and dG(C3)(2) derivatives, for which quartet-like and ribbon-like self-assembly has been unambiguously identified by (15)N refocused INADEQUATE spectra in a previous study of (15)N-labeled derivatives (Pham, T. N.; et al. J. Am. Chem. Soc.2005, 127, 16018). The NH (1)H chemical shift is observed to be higher (13-15 ppm) for ribbon-like self-assembly as compared to 10-11 ppm for a quartet-like arrangement, corresponding to a change from NH···N to NH···O intermolecular hydrogen bonding. The order of the two NH(2)(1)H chemical shifts is also inverted, with the NH(2) proton closest in space to the NH proton having a higher or lower (1)H chemical shift than that of the other NH(2) proton for ribbon-like as opposed to quartet-like self-assembly. For the dG(C3)(2) derivative for which a single-crystal diffraction structure is available, the distinct resonances and DQ peaks are assigned by means of gauge-including projector-augmented wave (GIPAW) chemical shift calculations. In addition, (14)N-(1)H correlation spectra obtained at 850 MHz under fast (60 kHz) magic-angle spinning (MAS) confirm the assignment of the NH and NH(2) chemical shifts for the dG(C3)(2) derivative and allow longer range through-space N···H proximities to be identified, notably to the N7 nitrogens on the opposite hydrogen-bonding face.