Simple peptidomimetic molecules derived from amino acids were reacted with meta- and para-bis(bromomethyl)benzene in acetonitrile to very efficiently yield macrocyclic structures. The cyclization reaction does not require high dilution techniques and seems to be insensitive to the size of the formed macrocycle. The analysis of data obtained by (1)H NMR, single-crystal X-ray diffraction, fluorescence measurements, and molecular mechanics indicate that folded conformations can preorganize the system for an efficient cyclization. The role played by intramolecular hydrogen-bonding and solvophobic effects in the presence of folded conformations is analyzed.

Acid test: Macrocyclic compounds that comprise a 9,10-anthracene subunit linked by a C2-symmetric peptidomimetic chain (see formula) are useful as fluorescent probes in a pH range of biomedical interest. Changes in the size of the macrocycle (n=3,4,6,8) produce a shift in the pKa values. Experiments with live mouse macrophage cells show the selective localization of the probe in the acidic organelles (see differential interference contrast image)

The ability of hexanuclear molybdenum cluster [Mo 6 I 8 (CH 3 COO) 6 ] 2to carry out, upon irradiation, singlet oxygen mediated photocatalytic oxygenation reactions has been tested. This complex has been also supported onto a solid polymeric matrix, yielding an immobilized photosensitizer with remarkable photostability and recyclability. Preliminary studies of antibacterial photoinactivation of Staphylococcus aureus have been conducted, with positive results.Photosensitization to produce reactive oxygen species (ROS) is widely used in a variety of fields, from photocatalysis to photodynamic therapy of cancer and photodynamic inactivation of microorganisms. In the first area, production of fine chemicals can be achieved by means of photocatalysed oxygenation reactions. 1 In the second realm, treatment of tumours or inactivation of bacteria can be done by the appropriate choice of photosensitizer and irradiation conditions. 2 For any application the requisite of photostability is of key importance and great effort is devoted to the development of photosensitizers resistant to the self-generated ROS species. 3 An outstanding library of photocatalytic and photodynamic agents has been developed so far. 4 Hexanuclear clusters of molybdenum [Mo 6 X 8 L 6 ] (X = Cl, Br, I; L is a ligand) are well known photochemical generators of singlet oxygen ( 1 O 2 ). 5

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