nan Miriam

C3 Vanadium(V) Amine Triphenolate Complexes: Vanadium Haloperoxidase Structural and Functional Models

The C 3 vanadium(V) amine triphenolate complex 1f has been characterized as a structural and functional model of vanadium haloperoxidases. The complex catalyzes efficiently sulfoxidations at room temperature using hydrogen peroxide as the terminal oxidant, yielding the corresponding sulfoxides in quantitative yields and high selectivities (catalyst loading down to 0.01%, TONs up to 9900, and TOFs up to 8000 h (-1)) as well as bromination of 1,3,5-trimethoxybenzene (catalyst loading down to 0.05%, TONs up to 1260, and TOFs up to 220 h (-1)).

Ti(IV)-amino triphenolate complexes as effective catalysts for sulfoxidation

C(3)-symmetric Ti(IV) amino triphenolate complexes efficiently catalyze, without previous activation and in excellent yields, the oxidation of sulfides at room temperature, using both CHP and the more environment friendly aqueous hydrogen peroxide as terminal oxidants, with catalyst loadings down to 0.01%. The Ti(IV) catalysts and the intermediate Ti(IV)-peroxo complexes have been characterized in solution by (1)H NMR and ESI-MS techniques and via density functional studies.

Stereoselective Control by Face‐to‐Face Versus Edge‐to‐Face Aromatic Interactions: The Case of C3‐TiIV Amino Trialkolate Sulfoxidation Catalysts

The stereoselective oxidation of differently functionalised benzyl phenyl sulfides has been examined by using enantiopure Ti(IV) trialkanolamine complexes. These complexes efficiently catalyse the sulfoxidation with good stereoselectivities. The data highlight the contribution to the stereoselectivity of steric effects and non-covalent pi-pi interactions between the aromatic rings of the Ti(IV) complex and those pertaining to the substrates. Enantiomeric excesses have been correlated with the electrostatic potential surfaces (EPS) of the reacting sulfides. The overall study leads to a mechanistic interpretation that explains the stereoselectivity of the system and dissects the role of aromatic and steric interactions in the stereoselective process.

Synthesis and self-assembly of oligo(p-phenylenevinylene) peptide conjugates in water.

Molecular self-organization is a useful approach to prepare soft and flexible, functional microand nanoarchitectures. A practical principle to self-assemble structures is based on simple p–p stacking of p-conjugated oligomers. Self-assembly (SA) of functionalized oligo(p-phenylenevinylene)s (OPVs) gives organogels with interesting photophysical properties and potential applications in light-emitting diodes, light-harvesting systems, or thermal imaging. However, organized, robust molecular structures are difficult to obtain by p–p stacking alone. Therefore, a variety of promoters that enable the establishment of additional noncovalent interactions, such as directional hydrogen bonds, have received increased attention. Among them, peptide amphiphiles, made of a p-conjugated unit and hydrophilic peptide sequences, have been considered because of their strong tendency to form well-defined secondary structures and to self-assemble in water. Herein, we report the synthesis and SA characteristics of two OPV peptide conjugates (OPV-1 and OPV-2, Scheme 1) in which a new OPV-based w-amino acid has been incorporated into two different b-sheet-forming sequences by solidphase synthesis. In these systems, a reversible SA can be triggered by pH changes. In particular, the ornithine-rich OPV-1 self-assembles at basic pH, whereas for OPV-2, which contains glutamic acid residues, SA occurs at acidic pH.

Stereoselective dimerization of racemic C3-symmetric Ti(IV) amine triphenolate complexes

A novel, mononuclear Ti(IV) amine triphenolate complex obtained by reaction of Ti(OiPr)(4) with tris(2-hydroxy-3-phenylbenzyl)amine bearing phenyl ortho-substituents affords quantitatively and spontaneously the corresponding heterochiral micro-oxo dinuclear compound whereas an analogous chiral, enantiopure complex maintains its mononuclear structure even in the presence of an excess of water.

Nanocrystalline cellulose–porphyrin hybrids: synthesis, supramolecular properties, and singlet-oxygen production

An amino-trisulfonate tetraphenylporphyrin was conjugated to carboxylate cellulose nanocrystals giving rise to a new nanomaterial with interesting binding properties.

Degradation Products from Naturally Aged Paper Leaves of a 16th-Century-Printed Book: A Spectrochemical Study

In this work, we present a wide-range spectrochemical analysis of the degradation products from naturally aged paper. The samples obtained from wash waters used during the de-acidification treatment of leaves from a 16th-century-printed book were analysed through NMR, IR, Raman UV/Vis, EPR and X-ray fluorescence (XRF) spectroscopy and HPLC-MS and inductively coupled plasma (ICP) analysis. By these methods we also studied some of the previous samples treated by acidification (sample AP) and catalytic hydrogenation (sample HP). Crossing all the data, we obtained precise indications about the main functional groups occurring on the degraded, water-soluble cellulose oligomers. These results point out that the chromophores responsible for browning are conjugated carbonyl and carboxyl compounds. As a whole, we show that the analysis of wash waters, used in the usual conservation treatments of paper de-acidification, gives much valuable information about both the conservation state of the book and the degradation reactions occurring on the leaves, due to the huge amount of cellulose by-products contained in the samples. We propose therefore this procedure as a new very convenient general method to obtain precious and normally unavailable information on the cellulose degradation by-products from naturally aged paper.

Templating the self-assembly of pristine carbon nanostructures in water.

The low solubility of carbon nanostructures (CNs) in water and the need of ordered architectures at the nanoscale level are two major challenges for materials chemistry. Here we report that a novel amino acid based low-molecular-weight gelator (LMWG) can be used to effectively disperse pristine CNs in water and to drive their ordered self-assembly into supramolecular hydrogels. A non-covalent mechanochemical approach has been used, so the π-extended system of the CNs remains intact. Optical spectroscopy and electron microscopy confirmed the effective dispersion of the CNs in water. Electron microscopy of the hydrogels showed the formation of an ordered, LMWG-assisted, self-assembled architecture. Moreover, the very same strategy allows the solubilization and self-assembly in water of a variety of hydrophobic molecules.

Photocontrolled Self‐Assembly of a Bis‐Azobenzene‐Containing α‐Amino Acid

Financial support from the Ministerio de Ciencia e Innovacion-FEDER (grant CTQ2010-17436, FPU fellowship to P.F.), Gobierno de Aragon-FSE (research group E40), and the University of Padova (PRAT A. M. C91 J11003560001 and M. M. CPDA119117) are gratefully acknowledged.

Synthesis and Electronic Properties of 1,2‐Hemisquarimines and Their Encapsulation in a Cucurbit[7]uril Host

The synthesis of a new class of robust squaraine dyes, colloquially named 1,2-hemisquarimines (1,2-HSQiMs), through the microwave-assisted condensation of aniline derivatives with the 1,2-squaraine core is reported. In CH3CN, 1,2-HSQiMs show a broad absorption band with a high extinction coefficient and a maximum at around λ=530u2005nm, as well as an emission band centered at about λ=574u2005nm, that are pH dependent. Protonation of the imine nitrogen causes a redshift of both absorption and emission maxima, with a concomitant increase in the lifetime of the emitting excited state. Encapsulation of the chromophore into a cucurbit[7]uril host revealed fluorescence enhancement and increased photostability in water. The redox characteristics of 1,2-HSQiMs indicate that charge injection into TiO2 is possible; this opens up promising perspectives for their use as photosensitizers for solar energy conversion.