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The synthesis of three new polyamine receptors based on a common 1,4,8,11-tetraazacyclododecane (cyclen) platform with appended, via a methylene linker, heteroaromatic fluorophores, a single quinoline (Q) or an 8-hydroxy-quinoline (8-OH-Q) moiety (L1 and HL2) or a Q and an 8-OH-Q unit (HL3), is reported. The proton binding features of these receptors, together with those of two similar receptors containing two equal Q moieties (L4) and two Q and two acetate groups (H2L5), have been studied by means of potentiometric, 1H NMR, UV-vis absorption and fluorescence emission measurements in aqueous solution at different pH values. While cyclen is a commonly used binding unit, Q and 8-OH-Q represent classical examples of signalling units in conjugated fluorescent chemosensors and their protonation features can strongly influence their ability in metal cations, and anion coordination and sensing. This study reveals that the structural features of these receptors are controlled by a subtle balance between hydrogen bonding and electrostatic repulsions occurring in their protonated species. At the same time, their emission properties are tuned by photoinduced electron and/or proton transfer processes taking place in the excited state.

A new tetraglyme adduct of sodium hexafluoroacetylacetonate [Na(hfa)·tetraglyme] has been synthesized and successfully used, together with the RE(hfa)3·diglyme (RE = Y, Yb, Er) complexes, in the synthesis of hexagonal phase NaYF4:Yb3+,Er3+ upconverting films through a facile sol–gel method.

Customized synthetic procedures for the obtainment of highly functionalizable free sulfonamide tricyclic structures having NH, O, S and SO2 (Z group) in the central seven-membered ring are presented. Due to the role that tricycles and the sulfonamide group play in medicinal chemistry, attention have been also paid to the 3D arrangement of these molecules. Their molecular structures and conformational properties have been studied by single-crystal X-ray diffraction and quantum chemical methods (HF-SCF/6-311+G(d,p). The minimum energy geometries in the solid state (I, Z = O; II, Z = NH and III, Z = S, SO2) have been compared with the minimum-energy geometries in the gas phase (invariably the type III geometry) and discussed with respect to the literature reference values. An effort was made to correlate the conformational differences observed in the solid-state and gas-phase with the nature of the Z grouping.

In the perspective of generating libraries for broad screening purposes, the inversion barrier of enantiomeric conformers of various tricyclic compounds, characterized by a seven-membered ring featuring a lactam group with two aromatics condensed at its opposite sides, has been investigated by ab initio calculations and NMR spectroscopy. Solid-state structure characterizations by single-crystal X-ray diffraction have been also carried out. The aim was to assess if moving from ethers to sulfides and sulfones derivatives, causes the racemization barrier to vary. Investigation was also extended to thiolactam congeners. Structural and electronic effects were investigated on the energetics of the inversion process and structure-property relationships evidenced. Results suggest that the ring inversion of the oxo derivatives is easier with respect to the corresponding S/SO2 ones. Also amide molecules have, on the whole, smaller barriers with respect to the corresponding thioamide ones.

The synthesis and characterization of the new tetraazamacrocycle 4-(N),10-(N)-bis[2-(3-hydroxy-2-oxo-2H-pyridin-1-yl)acetamido]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L) is reported. L shows two 3-(hydroxy)-1-(carbonylmethylen)-2(1H)-pyridinone moieties as side-arms of a tetra-aza-macrocyclic base. The key coupling of side-arms was studied and the most significant results were obtained by activating the 3-(benzyloxy)-1-(carboxymethyl)-2(1H)-pyridinone as pentafluorophenol ester. The acid–base properties of L and its capability to interact with simple ammonium cations were investigated by potentiometric measurements in aqueous solution (298.1 ± 0.1 K, I = 0.15 mol dm−3). Protonated species of L can bind NH4+ or primary ammonium cations such as MeNH3+ discriminating them from secondary or tertiary ammonium cations such as Me2NH2+ or Me3NH+ which are not bound in aqueous solution. 1 H and 13C NMR spectra showed the existence in solution of two conformers on the NMR time scale due to the rotational restriction of the two N–CO groups. The activation parameters were determined by dynamic variable-temperature NMR analysis.Molecular dynamics calculations gave results in agreement with the experimental data for both conformation and ammonium-binding studies, underlining that the transformation of the two secondary amines of the macrocyclic base to amide functions, forces the side-arms to remain fixed in position, almost face to face and thus to be preorganized to interact with other species. The crystal structure of the [HL]Cl·8H2O species shows the high number of preorganized hydrogen bond sites capable, in this case, of interacting directly with five H2O molecules.