Two aza scorpionand-like macrocycles (L2 and L3) have been prepared. L2 consists of a tren amine with two of its arms cyclizized with a 2,6-bis(bromomethyl)pyridine. In L3, the remaining pendant arm has been further functionalized with a fluorophoric naphthalene group. X-ray data on the compounds [H(L3)]ClO4.H2O (1) and [H3(L3)](H2PO4)3.H2O (2) as well as solution studies (pH-metry, UV-vis, and fluorescence data) show the movement of the pendant arm as a result of the protonation degree of the macrocycles and of the formation of intramolecular hydrogen bonds. X-ray data on the complexes [Cu(L2)](ClO4)2]2.H2O (3) and [Cu(L3)](ClO4)2 (4) and solution studies on Cu2+ coordination show the implication of the nitrogen of the arm in the binding to the metal ion. Kinetic studies on the decomposition and formation of the Cu2+ complexes provide additional information about the pH-dependent molecular reorganizations. Moreover, the obtained information suggests that the kinetics of the tail on/off process is essentially independent of the lability of the metal center.

The interaction of the open-chain polyamine N-(3-aminopropyl)- aminopropyl]ethane-1,2diamine (L) with the relevant anionic forms of adenosine 5Ј-triphosphate (ATP), adenosine 5Ј-diphosphate (ADP) and adenosine 5Ј-monophosphate (AMP) is described. Unambiguous criteria for defining thermodynamic selectivity based on the use of effective stability constants are presented. The interaction of L and several other topologically similar polyammonium receptors with ATP has been shown to occur through electrostatic and π-stacking intermolecular forces. The π-stacking binding mode is modulated by the protonation degree of ATP as indicated by fluorescence emission titrations. Evidence for the use of these receptors as ATP luminescent chemosensors is advanced.

CO2 is fixed by a Cu2+ complex of a macrocyclic terpyridinophane ligand forming a carbamate group. Several features of the structure mimic the enzyme rubisco.

A series of compounds made up by linking methylnaphthalene fragments at both ends of different polyamine chains have shown to behave as pH-regulated molecular machines driven by light and fluorescence emission studies have proved the formation of an excimer between the two naphthalene units whose appearance, fluorescence intensity and decay times depend on the pH value of the media.Many biological systems can be considered as more or less complex molecular machines operated by chemical or physical stimuli. Examples of this behaviour are found in the triggering effect of many calcium binding proteins or in the astonishing ATP synthase molecular rotor. 1,2 Therefore, in the last few years a lot of research effort has been devoted to identifying systems able to perform molecular motions following chemical or physical inputs. 1-9 Herewith, we communicate on a family of very simple compounds whose molecular movements driven by light can be controlled and even modulated by inputs like the concentration of hydrogen ions and/or metal ions. Compounds L1-L5 have been prepared in good yields by reaction of the elected polyamine with naphthalene-1-carbaldehyde in ethanol followed by reduction with sodium borohydride. 10 While the absorption spectra of these compounds do not change significantly with pH, the fluorescence emission intensity dramatically depends on their protonation state (see Fig. 1A for L1). As described for related compounds, 10 the fully protonated forms of L1-L5 exhibit the most intense fluorescence emission. Unprotonated amines are efficient electron transfer quenchers of the aromatic excited state and depending on the distance to the fluorophore can produce a partial or complete quenching. This trend is illustrated in Fig. 1B, where the fluorescence emission intensity monitored at 334 nm is plotted together with the mole fraction distribution of the different protonated species calculated from the protonation constants determined potentiometrically. 11 In order to have a full picture of the situation, the protonation sequence established for L1 by means of the 1 H and 13 C NMR data has to be taken into account. As shown in Fig. 1B, the first deprotonation that occurs on the central nitrogen atom leads to a partial quenching, ca. 80% of the emission of the fully protonated form. Total quenching takes place only upon removing the second proton from one of the side nitrogens. However, the most remarkable feature in the emission spectra of these compounds is the presence of a red-shifted and non-structured band attributable to excimer formation (Fig. 1A). This red shitted band does not appear in the case of the compound containing a single terminal naphthalene (L5), or in the case of an analogue receptor possessing a reinforcing piperazine ring (L6, see ESI). This absence in L5 excludes the possibility of a charge transfer (CT) state involving the deprotonated amine and the fluorophore. 12 Excimer formation is only observed for the H 2 L1 2+ species. Neither the fully protonated species H 3 L1 3+ nor the sp...