A Newly Designed Water Soluble Uranyl-Salophen Complex for Anion Recognition.

A novel water-soluble uranyl-salophen (salophen=N,N'-disalicylidene-o-phenylenediaminate) complex was obtained. Solubility was achieved in aqueous methyl-ß-cyclodextrin solutions, taking advantage of the host-guest interactions established with the adamantyl moieties present on the ligand skeleton. Such an approach facilitates the synthesis of the receptor and the purification processes and, in perspective, can be definitely applicable to other molecular scaffolds. UV/Vis titration experiments demonstrate that the capacity of the uranyl-salophen core to behave as a receptor for anions is retained in water and appears comparable with that previously reported for other water-soluble uranyl-salophen systems. Hence the presence of cyclodextrins does not interfere with molecular recognition processes.

Coordination-Driven Monolayer-to-Bilayer Transition in Two-Dimensional Metal-Organic Networks.

We report on monolayer-to-bilayer transitions in 2D metal-organic networks (MONs) from amphiphiles supported at the water-air interface. Functionalized calix[4]arenes are assembled through the coordination of selected transition metal ions to yield monomolecular 2D crystalline layers. In the presence of Ni(II) ions, interfacial self-assembly and coordination yields stable monolayers. Cu(II) promotes 2D coordination of a monolayer which is then diffusively reorganizing, nucleates, and grows a progressive amount of second layer islands. Atomic force microscopic data of these layers after transfer onto solid substrates reveal crystalline packing geometries with submolecular resolution as they are varying in function of the building blocks and the kinetics of the assembly. We assign this monolayer-to-bilayer transition to a diffusive reorganization of the initial monolayers owing to chemical vacancies of the predominant coordination motif formed by Cu2+ ions. Our results introduce a new dimension into the controlled monolayer-to-multilayer architecturing of 2D metal-organic networks.

Supramolecular architectures of molecularly thin yet robust free-standing layers.

Stable, single-nanometer thin, and free-standing two-dimensional layers with controlled molecular architectures are desired for several applications ranging from (opto-)electronic devices to nanoparticle and single-biomolecule characterization. It is, however, challenging to construct these stable single molecular layers via self-assembly, as the cohesion of those systems is ensured only by in-plane bonds. We herein demonstrate that relatively weak noncovalent bonds of limited directionality such as dipole-dipole (-CN⋅⋅⋅NC-) interactions act in a synergistic fashion to stabilize crystalline monomolecular layers of tetrafunctional calixarenes. The monolayers produced, demonstrated to be free-standing, display a well-defined atomic structure on the single-nanometer scale and are robust under a wide range of conditions including photon and electron radiation. This work opens up new avenues for the fabrication of robust, single-component, and free-standing layers via bottom-up self-assembly.

Modular synthesis and modification of novel bifunctional dendrons.

Herein, we report the design and synthesis of two novel bifunctional dendrons bearing multiple amine termini at the periphery and an azide at the focal point. Copper-catalyzed alkyne-azide cycloaddition enabled modular dendritic scaffold assembly resulting in a first generation dendron carrying six amines and a second generation dendron carrying eighteen amines. Peripheral amines were labeled with multiple copies of a metal isotope, whereas the azide functionality at the focal point was employed in conjugation to a single anti-human CD4 antibody. We demonstrated that the highly monomeric first generation dendron-antibody conjugate selectively detected CD4+ T cells in the PMBC culture.

Two-Dimensional Calix[4]arene-based Metal-Organic Coordination Networks of Tunable Crystallinity.

A flexible and versatile method to fabricate two-dimensional metal-organic coordination networks (MOCNs) by bottom-up self-assembly is described. 2D crystalline layers were formed at the air-water interface, coordinated by ions from the liquid phase, and transferred onto a solid substrate with their crystallinity preserved. By using an inherently three-dimensional amphiphile, namely 25,26,27,28-tetrapropoxycalix[4]arene-5,11,17,23-tetracarboxylic acid, and a copper metal node, large and monocrystalline dendritic MOCN domains were formed. The method described allows for the fabrication of monolayers of tunable crystallinity on liquid and solid substrates. It can be applied to a large range of differently functionalized organic building blocks, also beyond macrocycles, which can be interconnected by diverse metal nodes.

Interfacial binding of divalent cations to calixarene-based Langmuir monolayers.

The interactions of Langmuir monolayers produced through the self-assembly of an amphiphilic p-carboxycalix[4]arene (1) with a series of divalent, fourth-period transition metals, at the air-water interface, were investigated. Changes in the interfacial behavior of 1 in response to the presence of CuCl2, CoCl2, MnCl2, and NiCl2 were studied by means of Langmuir compression isotherms and Brewster angle microscopy (BAM). The measurements revealed that the self-assembly properties of 1 are significantly affected by Cu(2+) ions. The interactions of 1-based monolayers with Co(2+) and Cu(2+) ions were further investigated by means of synchrotron radiation-based X-ray reflectivity (XRR), X-ray near-total-reflection fluorescence (XNTRF), and grazing incidence X-ray diffraction (GIXD). XNTRF and XRR analyses revealed that the monolayer of 1 binds more strongly to Cu(2+) than Co(2+) ions. In the presence of relatively high concentrations of Cu(2+) ions in the subphase (1.4 × 10(-3) M), XNTRF exhibited anomalous depth profile behavior and GIXD measurements showed considerably strong diffuse scattering. Both measurements suggest the formation of Cu(2+) clusters contiguous to the monolayer of 1.

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.

Ipso-hydroxylation and subsequent fragmentation: a novel microbial strategy to eliminate sulfonamide antibiotics.

Sulfonamide antibiotics have a wide application range in human and veterinary medicine. Because they tend to persist in the environment, they pose potential problems with regard to the propagation of antibiotic resistance. Here, we identified metabolites formed during the degradation of sulfamethoxazole and other sulfonamides in Microbacterium sp. strain BR1. Our experiments showed that the degradation proceeded along an unusual pathway initiated by ipso-hydroxylation with subsequent fragmentation of the parent compound. The NADH-dependent hydroxylation of the carbon atom attached to the sulfonyl group resulted in the release of sulfite, 3-amino-5-methylisoxazole, and benzoquinone-imine. The latter was concomitantly transformed to 4-aminophenol. Sulfadiazine, sulfamethizole, sulfamethazine, sulfadimethoxine, 4-amino-N-phenylbenzenesulfonamide, and N-(4-aminophenyl)sulfonylcarbamic acid methyl ester (asulam) were transformed accordingly. Therefore, ipso-hydroxylation with subsequent fragmentation must be considered the underlying mechanism; this could also occur in the same or in a similar way in other studies, where biotransformation of sulfonamides bearing an amino group in the para-position to the sulfonyl substituent was observed to yield products corresponding to the stable metabolites observed by us.

Unsaturated beta-ketoesters as versatile electrophiles in organocatalysis.

Beta-ketoesters, which have widely been employed as nucleophiles, are also useful electrophiles in organocatalytic quinine mediated cascade reactions, leading to the formation of products bearing multiple stereocenters in high stereoselectivity.