The interaction of a neutral squaramide-based receptor, equipped with two 4-nitrophenyl substituents (R(sq)), with halides and oxoanions has been studied in MeCN. UV/Vis and (1)H NMR spectroscopy titration experiments clearly indicated the formation of 1:1 hydrogen bonding [R(sq)X](+) complexes with all the investigated anions. X-ray diffraction studies on the chloride and bromide complex salts confirmed the 1:1 stoichiometry and indicated the establishment of bifurcated hydrogen-bond interactions between the squaramide-based receptor and the halide anion that involved both 1) amide N-H and 2) aryl proximate C-H fragments, for a total of four bonds. Probably due to the contribution of C-H fragments, complexes of R(sq) with halides are 1 to 2 orders of magnitude more stable than the corresponding ones with the analogous urea-based receptor that contains two 4-nitrophenyl substituents (R(ur)). In the case of oxoanions, R(sq) forms complexes, the stability of which decreases with the decreasing basicity of the anion (H(2)PO(4) (-)>NO(2) (-) approximately HSO(4) (-)>NO(3) (-)), and is comparable to that of complexes of the urea-based receptor R(ur). Such a behaviour is ascribed to the predominance of different contributions: electrostatic interaction for halides, acid-to-base 'frozen' proton transfer for oxoanions. Finally, with the strongly basic anions F(-) and CH(3)COO(-), R(sq) first gives genuine hydrogen-bond complexes of 1:1 stoichiometry; then, upon addition of a second anion equivalent, it undergoes deprotonation of one N--H fragment, with the simultaneous formation of the dianion hydrogen-bond complexes, [HF(2)](-) and [CH(3)COOHCH(3)COO](-), respectively. In the case of the urea-based derivative R(ur), deprotonation takes place with fluoride but not with acetate. The apparently higher Brønsted acidity of R(sq) with respect to R(ur) reflects the capability of the squaramide receptor to delocalise the negative charge formed on N--H deprotonation over the cyclobutene-1,2-dione ring and the entire molecular framework.

Small extracellular vesicles (sEVs) present fairly distinctive lipid membrane features in the extracellular environment. These include high curvature, lipid-packing defects and a relative abundance in lipids such as phosphatidylserine and ceramide. sEV membrane could be then considered as a "universal" marker, alternative or complementary to traditional, characteristic, surface-associated proteins. Here, we introduce the use of membrane-sensing peptides as new, highly efficient ligands to directly integrate sEV capturing and analysis on a microarray platform. Samples were analysed by label-free, singleparticle counting and sizing, and by fluorescence co-localisation immune staining with fluorescent anti-CD9/anti-CD63/anti-CD81 antibodies. Peptides performed as selective yet general sEV baits and showed a binding capacity higher than anti-tetraspanins antibodies. Insights into surface chemistry for optimal peptide performances are also discussed, as capturing efficiency is strictly bound to probes surface orientation effects. We anticipate that this new class of ligands, also due to the versatility and limited costs of synthetic peptides, may greatly enrich the molecular toolbox for EV analysis.

The anion binding tendencies of the two fluorogenic ureas L(1)H and L(2)H, containing the 2-anthracenyl and 1-pyrenyl moieties as signaling units, respectively, have been investigated in MeCN and DMSO by absorption, emission, and (1)H NMR spectroscopies. The formation of stable 1:1 receptor:anion H-bond complexes has been confirmed by structural studies on the crystalline [Bu4N][L(1)···Cl] and [Bu4N][L(2)H···CH3COO] salts. Complexation induces significant variations of the emission properties of L(1)H and L(2)H according to a multifaceted behavior, which depends upon the fluorogenic substituent, the solvent, and the basicity of the anion. Poorly basic anions (Cl(-), Br(-)) cause a red shift of the emission band(s). Carboxylates (CH3COO(-), C6H5COO(-)) induce fluorescence quenching due to the occurrence of an electron-transfer process taking place in the locally excited complex [*L-H···X](-). However, this excited complex may undergo an intracomplex proton transfer from one urea N-H fragment to the anion, to give the tautomeric excited complex [L···H-X](-)*, which emits at higher wavelength. F(-) displays a unique behavior: It forms with L(1)H a stable [L-H···F](-) complex which in the excited state undergoes intracomplex proton transfer, to give the poorly emissive excited tautomer [L···H-F](-)*. With L(2)H, on moderate addition of F(-), the 1:1 H-bond complex forms, and the blue fluorescence of pyrene is quenched. Large excess addition of F(-) promotes deprotonation of the ground-state complex, according to the equilibrium [L(2)H···F](-) + F(-) ⇆ [L(2)](-) + HF2(-). The deprotonated receptor [L(2)](-) is distinctly emissive (yellow fluorescence), which generates the fluorimetric response ON(1)-OFF-ON(2) of receptor L(2)H with respect to F(-).

Too hot to handle: Unprecedented affinity and specificity for (99)TcO(4)(-) in aqueous solution was shown with the p-xylyl azacryptand in the hexaprotonated form. A crystal structure of the complex reveals how the anion fits within the cavity of the cage, and the formation of multiple H-bond interactions with protonated amino groups stabilize the adduct.

The dimetallic cryptate [Cu(2)(II)(1)](4+) selectively recognizes guanosine monophosphate with respect to other nucleoside monophosphates (NMPs) in a MeOH/water solution at pH 7. Recognition is efficiently signaled through the displacement of the indicator 6-carboxyfluorescein bound to the receptor, monitoring its yellow fluorescent emission. Titration experiments evidenced the occurrence of several simultaneous equilibria involving 1:1 and 2:1 receptor/NMP and receptor/indicator complexes. It was demonstrated that the added NMP displaces the indicator from the 2:1 receptor/indicator complex, forming the 1:1 receptor/analyte inclusion complex. Recognition selectivity is thus ascribed to the nature of nucleotide donor atoms involved in the coordination and their ability to encompass the Cu(II)-Cu(II) distance within the cryptate.