A supramolecular approach for the specific detection of sarcosine, recently linked to the occurrence of aggressive prostate cancer forms, has been developed. A hybrid active surface was prepared by the covalent anchoring on Si substrates of a tetraphosphonate cavitand as supramolecular receptor and it was proven able to recognize sarcosine from its nonmethylated precursor, glycine, in water and urine. The entire complexation process has been investigated in the solid state, in solution, and at the solid-liquid interface to determine and weight all the factors responsible of the observed specificity. The final outcome is a Si-based active surface capable of binding exclusively sarcosine. The complete selectivity of the cavitand-decorated surface under these stringent conditions represents a critical step forward in the use of these materials for the specific detection of sarcosine and related metabolites in biological fluids. molecular recognition | phosphonate cavitand

We describe the design, synthesis and conformational assignment of three diasteromeric bis-phosphonate cavitands based on an aryl extended calix[4]pyrrole tetrol scaffold. The diastereoisomers differ in the relative spatial orientation of the P═O groups installed at their upper rims. We demonstrate that these compounds act as heteroditopic receptors for ion pairs forming ion-paired 1:1 complexes with alkylammonium (quaternary and primary) chloride salts in dichloromethane (DCM) solution and in the solid-state. (1)H NMR titrations indicate that the complexes are highly stable thermodynamically and kinetically. In the case of tetraalkyl-phosphonium/ammonium chloride guests, the host featuring the two P═O groups directed outwardly with respect to the aromatic cavity, 4oo, produces the most thermodynamically stable complexes. Conversely, for the primary alkyl ammonium chloride, the most effective receptor is the diastereoisomer 4ii with the two P═O groups converging on top of the aromatic cavity. In the nonpolar DCM solvent, the size of the quaternary cation has a strong impact in the thermodynamic stability of the complexes and their binding geometry. We use 2D-ROESY experiments to map out the binding geometries of the 1:1 complexes formed in solution. The 1:1 complexes of the 4oo host with the chloride salts have a separated arrangement of the bound ion-pair. In contrast, those of the 4ii host display a close-contact arrangement. We also investigate the same complexation processes in acetonitrile (ACN) solution. Both the salt and the initially formed anionic complex are fully dissociated in this more polar solvent. The receptors show an analogous trend in their binding affinities for quaternary phosphonium/ammonium chloride salts to the one seen in DCM solution. However, in ACN solution, the magnitudes of the binding affinities are reduced significantly and the size of the cation does not play a role. In addition, the inversion in the trend of relative binding affinities of the complexes, which was revealed in DCM solution, is eradicated in ACN when changing the cation substitution from quaternary to primary.

No abstract

The zinc(II) complexes reported here have been synthesised from the ligand 4‐methyl‐2‐N‐(2‐pyridylmethyl)aminophenol (Hpyramol) with chloride or acetate counterions. All the five complexes have been structurally characterised, and the crystal structures reveal that the ligand Hpyramol gradually undergoes an oxidative dehydrogenation to form the ligand 4‐methyl‐2‐N‐(2‐pyridylmethylene)aminophenol (Hpyrimol), upon coordination to ZnII. All the five complexes cleave the ϕX174 phage DNA oxidatively and the complexes with fully dehydrogenated pyrimol ligands were found to be more efficient than the complexes with non‐dehydrogenated Hpyramol ligands. The DNA cleavage is suggested to be ligand‐based, whereas the pure ligands alone do not cleave DNA. The DNA cleavage is strongly suggested to be oxidative, possibly due to the involvement of a non‐diffusible phenoxyl radical mechanism. The enzymatic religation experiments and DNA cleavage in the presence of different radical scavengers further support the oxidative DNA cleavage by the zinc(II) complexes.

Phosphonate cavitands are an emerging class of synthetic receptors for supramolecular sensing. The molecular recognition properties of the third-generation tetraphosphonate cavitands toward alcohols and water at the gas-solid interface have been evaluated by means of three complementary techniques and compared to those of the parent mono- and diphosphonate cavitands. The combined use of ESI-MS and X-ray crystallography defined precisely the host-guest association at the interface in terms of type, number, strength, and geometry of interactions. Quartz crystal microbalance (QCM) measurements then validated the predictive value of such information for sensing applications. The importance of energetically equivalent multiple interactions on sensor selectivity and sensitivity has been demonstrated by comparing the molecular recognition properties of tetraphosphonate cavitands with those of their mono- and diphosphonate counterparts.

A series of isostructural three-dimensional metal-organic frameworks [Pr(2)(N-BDC)(3)(dmf)(4)](infinity) (1), {[Eu(2)(N-BDC)(3)(dmf)(4)] x 2DMF}(infinity) (2 x 2DMF), [Gd(2)(N-BDC)(3)(dmf)(4)](infinity) (3), {[Tb(2)(N-BDC)(3)(dmf)(4)] x 2DMF}(infinity) (4 x 2DMF), {[Dy(2)(N-BDC)(3)(dmf)(4)] x 2DMF}(infinity) (5 x 2DMF) (N-H(2)BDC = 2-amino-1,4-benzenedicarboxylic acid; DMF = N,N'-dimethylformamide) with cubic 4(12) x 6(3) topology have been synthesized using solvothermal conditions. The networks were generated via formation of a dinuclear Ln(2) secondary building block, involving the dicarboxylate ligand as a bridge. The luminescent properties of the Tb(III) and Eu(III) complexes were studied and showed characteristic emissions at room temperature. Antiferromagnetic interactions between Ln(III) ions were observed from magnetic susceptibility data.

The reaction of Zn(NO3)2.6H2O or Cu(NO3)2.3H2O with the star-shaped ligand 2,4,6-tris(di-2-picolylamino)[1,3,5]triazine (dipicatriz) in acetonitrile results in the formation of the mono- or trinuclear coordination compounds [Zn(dipicatriz)(NO3)2] (1), [Zn3(dipicatriz)(NO3)6](CH3CN)3 (2), and [Cu3(dipicatriz)(NO3)2(H2O)6](NO3)4 (3), depending on the metal-to-ligand ratios used during the crystallization process. Their crystal structures exhibit unique supramolecular interactions. Compounds 1 and 2 show anion-pi interactions between coordinated nitrate ions and the s-triazine ring. Compound 3 exhibits remarkable interactions between two noncoordinated nitrate anions and the two faces of the electron-deficient heteroaromatic ring, corroborating earlier theoretical investigations in this area. New theoretical investigations have been carried out on nitrate-pi interactions, taking into account the particular position of the anion toward the aromatic ring observed in the crystal structures.

A Si(100) surface featuring molecular recognition properties was obtained by covalent functionalization with a tetraphosphonate cavitand (Tiiii), able to complex positively charged species. Tiiii cavitand was grafted onto the Si by photochemical hydrosilylation together with 1-octene as a spatial spectator. The recognition properties of the Si-Tiiii surface were demonstrated through two independent analytical techniques, namely XPS and fluorescence spectroscopy, during the course of reversible complexation-guest exchange-decomplexation cycles with specifically designed ammonium and pyridinium salts. Control experiments employing a Si(100) surface functionalized with a structurally similar, but complexation inactive, tetrathiophosphonate cavitand (TSiiii) demonstrated no recognition events. This provides evidence for the complexation properties of the Si-Tiiii surface, ruling out the possibility of nonspecific interactions between the substrate and the guests. The residual Si-O(-) terminations on the surface replace the guests' original counterions, thus stabilizing the complex ion pairs. These results represent a further step toward the control of self-assembly of complex supramolecular architectures on surfaces.