Synthesis of Bodipy-Tagged Galactoconjugates and Evaluation of Their Antibacterial Properties.

As a development of our research on biocompatible glycoconjugate probes and specifically multi-chromophoric systems, herein, we report the synthesis and early bactericidal tests of two luminescent glycoconjugates whose basic structure is characterized by two boron dipyrromethene difluoride (BODIPY) moieties and three galactoside rings mounted on an oligophenylene ethynylene (OPE) skeleton. BODIPY fluorophores have found widespread application in many branches of biology in the last few decades. In particular, molecular platforms showing two different BODIPY groups have unique photophysical behavior useful in fluorescence imaging.

Photophysical Properties of Homo- and Hetero-Aggregate Assemblies Made of N-Annulated Perylene Derivatives.

We report the absorption spectra and photophysical properties of homo and hetero-aggregate assemblies of a strongly emissive N-annulated perylene dye (P) and of a dyad made of P and a methyl viologen derivative (P-MV), in ethanol-water solutions. In homo-aggregate assemblies of P, the π-π* fluorescence of the isolated chromophore is replaced by excimer emission at lower energy, with a lifetime of 900 ps, due to excimer formation from the initially prepared excitons. In homo-aggregate assemblies of P-MV, photoinduced charge separation, with formation of P -MV species, occurs in 3 ps with a charge recombination of 20 ps.

Photocatalyzed CO reduction to CO by supramolecular photocatalysts made of Ru(II) photosensitizers and Re(I) catalytic subunits containing preformed COTEOA adducts.

Two new supramolecular photocatalysts containing Ru(II) polypyridine units as light-harvesting photosensitizers and Re(I) polypyridine subunits as catalytic centers have been prepared. The new species, RuRe2A and Ru2ReA, contain catalytic Re(I) subunits coordinated by the preformed COTEOA adduct (known to be the effective catalytic subunits; TEOA is triethanolamine) and exhibit quite efficient and selective photoreduction of CO to CO, with outstanding TONs of 2368 and 2695 and a selectivity of 99.9% and 98.

Amino-OPE glycosides and blue light: a powerful synergy in photodynamic therapy.

Herein we report the synthesis and biological properties of sugar-conjugated oligophenylene ethynylene (OPE) dyes, used as novel photosensitizers (PSs) for photodynamic treatment (PDT) under blue light. The OPE-bearing glycosides at both ends are successfully prepared by a Pd-catalyzed Sonogashira cross-coupling reaction. The live-cell imaging studies have shown that these OPE glycosides (including glucose, mannose and maltose derivatives) efficiently penetrate the cytoplasm of cultured HeLa cancer cells.

Self-assembled systems for artificial photosynthesis.

The last few decades have seen an impressive development in molecular-based artificial photosynthesis, thanks to the design of integrated light-harvesting antennae, charge separation systems, and catalysts for water oxidation or hydrogen production based on covalently linked subunits. However, in recent years, self-assembly and spontaneous aggregation of components emerged - sometimes also through serendipity - for the preparation of multicomponent systems aimed to perform the basic processes needed for artificial photosynthesis. Here we critically discuss some key articles that have recently shown the potential of self-assembly for artificial photosynthesis, ranging from self-assembly of antennae and charge separation systems to integrated antenna/catalyst assemblies, to planned co-localization of various components into restricted environments.

A Curcumin-BODIPY Dyad and Its Silica Hybrid as NIR Bioimaging Probes.

In this paper we describe the synthesis of a novel bichromophoric system in which an efficient photoinduced intercomponent energy transfer process is active. The dyad consists of one subunit of curcumin and one of BODIPY and is able to emit in the far-red region, offering a large Stokes shift, capable of limiting light scattering processes for applications in microscopy. The system has been encapsulated in MCM-41 nanoparticles with dimensions between 50 and 80 nm.

Bodipy-carbohydrate systems: synthesis and bio-applications.

Luminescent BODIPY-sugar probes have stimulated the attention of researchers for the potential applications of such molecular systems in bio-imaging. The presence of carbohydrate units confers unique structural and biological features, beside enhancement of water solubility and polarity. On the other hand, BODIPY (BOronDiPYrromethene) derivatives represent eclectic and functional luminescent molecules because of their outstanding photophysical properties.

Molecular Modelling and Simulations of Light-Harvesting Decanuclear Ru-Based Dendrimers for Artificial Photosynthesis.

The structure of a decanuclear photo- and redox-active dendrimer based on Ru(II) polypyridine subunits, suitable as a light-harvesting multicomponent species for artificial photosynthesis, has been investigated by means of computer modelling. The compound has the general formula [Ru{(μ-dpp)Ru[(μ-dpp)Ru(bpy) ] } ](PF ) (Ru10; bpy=2,2'-bipyridine; dpp=2,3-bis(2'-pyridyl)pyrazine). The stability of possible isomers of each monomer was investigated by performing classical molecular dynamics (MD) and quantum mechanics (QM) simulations on each monomer and comparing the results.

Photoinduced Water Oxidation in Chitosan Nanostructures Containing Covalently Linked Ru Chromophores and Encapsulated Iridium Oxide Nanoparticles.

The luminophore Ru(bpy) (dcbpy) (bpy=2,2'-bipyridine; dcbpy=4,4'-dicarboxy-2,2'-bipyridine) is covalently linked to a chitosan polymer; crosslinking by tripolyphosphate produced Ru-decorated chitosan fibers (NS-RuCh), with a 20 : 1 ratio between chitosan repeating units and Ru chromophores. The properties of the Ru compound are unperturbed by the chitosan structure, with NS-RuCh exhibiting the typical metal-to-ligand charge-transfer (MLCT) absorption and emission bands of Ru complexes. When crosslinks are made in the presence of IrO nanoparticles, such species are encapsulated within the nanofibers, thus generating the IrO ⊂NS-RuCh system, in which both Ru photosensitizers and IrO water oxidation catalysts are within the nanofiber structures.

Fast transport of HCl across a hydrophobic layer over macroscopic distances by using a Pt(II) compound as the transporter: micro- and nanometric aggregates as effective transporters.

Bis-(diethyl-dithioxamidate)platinum(ii) is able to transport HCl from the donor aqueous phase to the receiving one over a mean distance of 12 cm in about 3 minutes across an organic membrane in the bulk, without stirring of the organic phase, i.e. at a rate far exceeding the unidirectional macroscopic diffusion coefficient.

Efficient trinuclear Ru(ii)-Re(i) supramolecular photocatalysts for CO reduction based on a new tris-chelating bridging ligand built around a central aromatic ring.

We have designed and synthesized a new tris-chelating polypyridine ligand () suitable to be used as a bridging ligand (BL) for constructing various supramolecular photocatalysts. This BL is a phenylene ring with three ethylene chains at 1, 3, and 5 positions, of which the other terminals are connected to 2,2'-bipyridine moieties. The ligand has been used to prepare, according to a multi-step synthetic protocol, trinuclear supramolecular photocatalysts containing different metal subunits.

Ru(ii) water oxidation catalysts with 2,3-bis(2-pyridyl)pyrazine and tris(pyrazolyl)methane ligands: assembly of photo-active and catalytically active subunits in a dinuclear structure.

Two mononuclear Ru(ii) complexes, i.e. [RuCl(κN-terpy)(κN-dpp)]PF ([1]PF; terpy = 2,2':6',2''-terpyridine; dpp = 2,3-bis(2'-pyridyl-pyrazine) and [RuCl(κN-tpm)(κN-dpp)]Cl ([2]Cl; tpm = tris(1-pyrazolyl)methane), and one dinuclear complex, i.

Designing expanded bipyridinium as redox and optical probes for DNA.

We report on the light-switch behaviour of two head-to-tail expanded bipyridinium species as a function of their interaction with calf thymus DNA and polynucleotides. In particular, both DNA and polynucleotides containing exclusively adenine or guanine moieties quench the luminescence of the fused expanded bipyridinium species. This behaviour has been rationalized demonstrating that a reductive photoinduced electron transfer process takes place involving both adenine or guanine moieties.

Photoinduced Intercomponent Processes in Selectively Addressable Bichromophoric Dyads Made of Linearly Arranged Ru(II) Terpyridine and Expanded Pyridinium Components.

Three new linearly arranged bichromophoric systems 1-3 have been prepared, and their photophysical properties have been studied, taking also advantage of femtosecond pump-probe transient absorption spectroscopy. The three compounds contain the same chromophores, that is a Ru(II)-terpy-like species and a fused expanded bipyridinium (FEBP) unit, separated by three different, variously methylated biphenylene-type bridges. The chromophores have been selected to be selectively addressable, and excitation involving the Ru-based or the FEBP-based dyes results in different excited-state decays.

Carbohydrates and Charges on Oligo(phenylenethynylenes): Towards the Design of Cancer Bullets.

Two new tetralkylammonium-OPEs, bearing one or two positively charged groups directly linked to the aromatic residues and two β-d-glucopyranose terminations, were synthesized. Their peculiar structural features, joining the biologically relevant sugar moieties, flat aromatic cores and positive charges, make these luminescent dyes soluble in aqueous media and able to strongly interact with DNA. As a result of UV/Vis spectral variations, DNA melting temperature measures, viscometric titrations and induced CD, we propose a partial insertion of the OPEs aromatic core into the helix, stabilized by glucose H-bonding with the groups accessible from the grooves.

Localization-controlled two-color luminescence imaging via environmental modulation of energy transfer in a multichromophoric species.

We prepared a bichromophoric species 1, made of two different bodipy dyes bridged by a d-galactose unit. 1 exhibits different emission spectra when located in different compartments of biological systems, independently of its concentration. This is an unprecedented feature for a single multicomponent molecule and is due to the dependence on the environment of the photoinduced energy transfer process occurring between its bodipy subunits.

Photo-Induced Assembly of a Luminescent Tetraruthenium Square.

Self-assembly is a powerful synthetic tool that has led to the development of one-, two- and three-dimensional architectures. From MOFs to molecular flasks, self-assembled materials have proven to be of great interest to the scientific community. Here we describe a strategy for the construction and de-construction of a supramolecular structure through unprecedented photo-induced assembly and dis-assembly.

A water-soluble pillar[5]arene as a new carrier for an old drug.

The remarkable affinity of deca-carboxylatopillar[5]arene WP5 towards the aminoglycoside antibiotic, amikacin, in aqueous media is reported; in vitro studies on Gram-positive bacteria (Staphylococcus aureus) show that drug entrapment inside WP5 also takes place in the presence of the microrganisms, thus pointing to WP5 as an appealing carrier for amikacin targeted delivery.

A heptanuclear light-harvesting metal-based antenna dendrimer with six Ru(ii)-based chromophores directly powering a single Os(ii)-based energy trap.

The novel dendritic-shaped, heptanuclear compound 1 - the first mixed Os-Ru dendrimer with tris-chelating bridging ligands - has been synthesized and its photophysics studied by fs pump-probe transient spectroscopy. In 1, all light energy absorbed by six identical Ru(ii) chromophores is funnelled to the luminescent central Os(ii) core, with a time constant of 11 ps, by Dexter energy transfer.

Glucose-functionalized amino-OPEs as biocompatible photosensitizers in PDT.

Photodynamic therapy (PDT) is a minimally invasive procedure that can provide a selective eradication of neoplastic diseases by the combined effect of a photosensitizer, light and oxygen. New amino oligo(phenylene-ethynylene)s (OPEs), bearing hydrophilic glucoside terminations, have been prepared, characterized and tested as photosensitizers in PDT. The effectiveness of these compounds in combination with UVA light has been checked on two tumor cell lines (HEp-2 and HeLa cells, derived from a larynx carcinoma and a cervical carcinoma, respectively).

Water oxidation catalysis upon evolution of molecular Co(III) cubanes in aqueous media.

The increasing global energy demand has stimulated great recent efforts in investigating new solutions for artificial photosynthesis, a potential source of clean and renewable solar fuel. In particular, according to the generally accepted modular approach aimed at optimising separately the different compartments of the entire process, many studies have focused on the development of catalytic systems for water oxidation to oxygen. While in recent years there have been many reports on new catalytic systems, the mechanism and the active intermediates operating the catalysis have been less investigated.

Photoinduced Charge Separation in a Donor-Spacer-Acceptor Dyad with N-Annulated Perylene Donor and Methylviologen Acceptor.

The first donor-acceptor species in which a strongly emissive N-annulated perylene dye is connected to a methylviologen electron acceptor unit via its macrocyclic nitrogen atom, is prepared by a stepwise, modular procedure. The absorption spectra, redox behavior, spectroelectrochemistry and photophysical properties of this dyad and of its model species are investigated, also by pump-probe fs transient absorption spectroscopy. Photoinduced oxidative electron transfer from the excited state of the dyad, centered on the N-annulated perylene subunit, to the appended methyviologen electron acceptor takes place in a few ps.

Polyimide dendrimers containing multiple electron donor-acceptor units and their unique photophysical properties.

A high-yielding synthesis of a series of polyimide dendrimers, including decacyclene- and perylene-containing dendrimer D6, in which two types of polyimide dyes are present, is reported. In these constructs, the branching unit is represented by trisphenylamine, and the solubilizing chains by N-9-heptadecanyl-substituted perylene diimides. The photophysical properties of the dendrimers have been studied by absorption, steady-state, and time-resolved emission spectroscopy and pump-probe transient absorption spectroscopy.