A robust heterodimeric bis-Rh(III)-porphyrin macrocycle for the self-assembly of a kinetically stable [2]-rotaxane.

We report the self-assembly of a robust di-nuclear tetralactam macrocyle based on two symmetric components: a Rh(III) bis-porphyrin and a bis-pyridyl ligand. We probe the binding properties of the tetralactam macrocycle with adipamide derivatives using 1H NMR spectroscopy. On the one hand, we show that the binding of the adipamide having linear alkyl chains that can thread through the intact macrocycle's cavity produces a weakly bound 1 : 1 complex stabilized by four intermolecular hydrogen bonds and featuring a preferred binding geometry of [2]pseudorotaxane topology. On the other hand, we detect the formation of two different complexes in the binding of an analogous adipamide possessing bulky stoppers (dumb-bell axle). The initial addition of the dumb-bell guest induces the formation of a 1 : 1 complex featuring fast exchange kinetics on the 1H chemical shift timescale and exo-cyclic (non-threaded) binding geometry. Notably, in the presence of a large excess of the dumb-bell guest and at suitable concentrations of the macrocycle (>5 mM) we observe the emergence of a second species displaying slow exchange kinetics. This observation allows the undisputed assignment of a [2]rotaxane topology to the second complex. The significant increase in kinetic stability featured by the di-nuclear Rh(III) [2]rotaxane complex contrasts with its reduction in thermodynamic stability (more than one order of magnitude) compared to the previously described di-nuclear Zn(II) counterpart.

Thiourea- and Amino-Substituted Benzoxadiazole Dyes with Large Stokes Shifts as Red-Emitting Probe Monomers for Imprinted Polymer Layers Targeting Carboxylate-Containing Antibiotics.

Bifunctional fluorescent molecular oxoanion probes based on the benzoxadiazole (BD) chromophore are described which integrate a thiourea binding motif and a polymerizable 2-aminoethyl methacrylate unit in the 4,7-positions of the BD core. Concerted charge transfer in this electron donor-acceptor-donor architecture endows the dyes with strongly Stokes shifted (up to >250 nm) absorption and fluorescence. Binding of electron-rich carboxylate guests at the thiourea receptor leads to further analyte-induced red-shifts of the emission, shifting the fluorescence maximum of the complexes to ≥700 nm. Association constants for acetate are ranging from 1-5×105  M-1 in acetonitrile. Integration of one of the fluorescent probes through its polymerizable moiety into molecularly imprinted polymers (MIPs) grafted from the surface of submicron silica cores yielded fluorescent MIP-coated particle probes for the selective detection of antibiotics containing aliphatic carboxylate groups such as enoxacin (ENOX) at micromolar concentrations in highly polar solvents like acetonitrile.

Development of a "Turn-on" Fluorescent Probe-Based Sensing System for Hydrogen Sulfide in Liquid and Gas Phase.

A "turn-on" fluorescence sensing system based on a BODIPY-cobaloxime complex for the detection of H2S in liquid and gas phase was developed. To that aim, two cobaloxime complexes bearing an axial pyridyl-BODIPY ligand were initially evaluated as sensitive fluorescent HS- indicators in aqueous solution. The sensing mechanism involves the selective substitution of the BODIPY ligand by the HS- anion at the cobalt center, which is accompanied by a strong fluorescence enhancement. The selection of a complex with an ideal stability and reactivity profile toward HS- relied on the optimal interaction between the cobalt metal-center and two different pyridyl BODIPY ligands. Loading the best performing BODIPY-cobaloxime complex onto a polymeric hydrogel membrane allowed us to study the selectivity of the probe for HS- against different anions and cysteine. Successful detection of H2S by the fluorescent "light-up" membrane was not only accomplished for surface water but could also be demonstrated for relevant H2S concentrations in gas phase.

Multivalency in Heteroternary Complexes on Cucurbit[8]uril-Functionalized Surfaces: Self-assembly, Patterning, and Exchange Processes.

The spatial confinement of multivalent azopyridine guest molecules mediated by cucurbit[8]urils is described. Fluorescent dye-labelled multivalent azopyridine molecules were attached to preformed methyl viologen/cucurbit[8]uril inclusion complexes in solution and at surfaces. The formation of the resulting heteroternary host-guest complexes was verified in solution and on gold substrates. Surface binding constants of the multivalent ligands were two orders of magnitude higher than that of the monovalent one. Poly-l-lysine grafted with oligo(ethylene glycol) and maleimide moieties was deposited on cyclic olefin polymer surfaces and further modified with thiolated methyl viologen and cucurbit[8]uril. Defined micrometer-sized patterns were created by soft lithographic techniques. Supramolecular exchange experiments were performed on these surface-bound heterocomplexes, which allowed the creation of cross-patterns by taking advantage of the molecular valency, which led to the substitution of the monovalent guest by the multivalent guests but not vice versa.

Sensitive Assays by Nucleophile-Induced Rearrangement of Photoactivated Diarylethenes.

Upon light-induced isomerization, diarylethenes (DAEs) equipped with reactive aldehyde moieties rearrange selectively in the presence of amines, accompanied by decoloration. In a comprehensive study, the probe structure was optimized with regard to its inherent reactivity in the nucleophile-triggered rearrangement reaction. Detailed structure-reactivity relationships could be derived, in particular with regard to the type of integrated (het)aryl moieties as well as the location of the formyl residue, and the probes' intrinsic reactivity with primary and secondary amines was optimized. Utilizing an ancillary base, the initially formed rearrangement product can engage in a subsequent catalytic cycle, leading to an amplified decoloration process. This additional catalytic pathway allows us to enhance the sensitivity of our method and successfully discriminate between amines and thiols. Moreover, probes that exhibit strong analyte-induced fluorescence modulation have been designed to further decrease the detection limit by using a more sensitive read-out. The optimized DAE probes are promising molecular components for future programmable sensing materials and devices.

Light-Activated Sensitive Probes for Amine Detection.

Our new, simple, and accurate colorimetric method is based on diarylethenes (DAEs) for the rapid detection of a wide range of primary and secondary amines. The probes consist of aldehyde- or ketone-substituted diarylethenes, which undergo an amine-induced decoloration reaction, selectively to give the ring-closed isomer. Thus, these probes can be activated at the desired moment by light irradiation, with a sensitivity that allows the detection of amines at concentrations as low as 10-6 m in solution. In addition, the practical immobilization of DAEs on paper makes it possible to detect biogenic amines, such as cadaverine, in the gas phase above a threshold of 12 ppbv within 30 seconds.

Ordered co-encapsulation of chloride with polar neutral guests in a tetraurea calix[4]pyrrole dimeric capsule.

In this work, we describe the stoichiometrically controlled self-assembly process of tetraurea calix[4]pyrrole 1 with a polar neutral guest, trimethylamine N-oxide or beta-alanine betaine, and methyltrioctylammonium chloride (MTOACl) salt into two supramolecular architectures which differ in morphology and stoichiometry. Whereas an equimolar solution of tetraurea calixpyrrole 1, polar guest and MTOACl produces a four-particle inclusion assembly, a mixture of the same components in a 2 : 1 : 1 molar ratio induces the formation of a dimeric capsular assembly displaying multiple guests which are orderly co-encapsulated. The influence of other polar guests and ammonium salts on the self-assembly process is also described.

Influence of the solvent and metal center on supramolecular chirality induction with bisporphyrin tweezer receptors. Strong metal modulation of effective molarity values.

We describe the synthesis of a bisporphyrin tweezer receptor 1·H(4) and its metalation with Zn(II) and Rh(III) cations. We report the thermodynamic characterization of the supramolecular chirality induction process that takes place when the metalated bisporphyrin receptors coordinate to enantiopure 1,2-diaminocyclohexane in two different solvents, toluene and dichloromethane. We also performed a thorough study of several simpler systems that were used as models for the thermodynamic characterization of the more complex bisporphyrin systems. The initial complexation of the chiral diamine with the bisporphyrins produces a 1:1 sandwich complex that opens up to yield a simple 1:2 complex in the presence of excess diamine. The CD spectra associated with the 1:1 and 1:2 complexes of both metalloporphyrins, 1·Zn(2) and 1·Rh(2), display bisignate Cotton effects when the chirogenesis process is studied in toluene solutions. On the contrary, in dichloromethane solutions, only 1·Zn(2) yields CD-active 1:1 and 1:2 complexes, while the 1:2 complex of 1·Rh(2) is CD-silent. In both solvents, porphyrin 1·Zn(2) features a stoichiometrically controlled chirality inversion process, which is the sign of the Cotton effect of the 1:1 complex is opposite to that of the 1:2 complex. In contrast, porphyrin 1·Rh(2) affords 1:1 and 1:2 complexes in toluene solutions with the same sign for their CD couplets. Interestingly, in both solvents, the signs of the CD couplets associated with the 1:1 sandwich complexes of 1·Zn(2) and 1·Rh(2) are opposite. The amplitudes of the CD couplets are higher for 1·Zn(2) than for 1·Rh(2). This observation is in agreement with 1·Rh(2) having a smaller extinction coefficient than 1·Zn(2). We performed DFT-based calculations and assigned molecular structures to the 1:1 and 1:2 complexes that explain the observed signs for their CD couplets. Unexpectedly, the quantification of the thermodynamic stability of the two metallobisporphyrin/diamine 1:1 sandwich complexes revealed the existence of interplay between effective molarity values (EM) and the strength of the intermolecular interaction (K(m); N···Zn or N···Rh) used in their assembly. The EM for the N···Rh(III) intramolecular interaction is 3 orders of magnitude smaller than that for the N···Zn(II) interaction, both of which are embedded in the same scaffold of the 1·M(2) bisporphyrin receptor.

Polyatomic anion assistance in the assembly of [2]pseudorotaxanes.

We describe the use of polyatomic anions for the quantitative assembly of ion-paired complexes displaying pseudorotaxane topology. Our approach exploits the unique ion-pair recognition properties exhibited by noncovalent neutral receptors assembled through hydrogen-bonding interactions between a bis-calix[4]pyrrole macrocycle and linear bis-amidepyridyl-N-oxides. The complexation of bidentate polyatomic anions that are complementary in size and shape to the receptor's cavity, in which six NH hydrogen-bond donors converge, induces the exclusive formation of four particle-threaded assemblies.