Self-Assembly and Electrical Conductivity of a New [1]benzothieno[3,2-b][1]-benzothiophene (BTBT)-Peptide Hydrogel.

The conjugation of small-molecule semiconductors with self-assembling peptides is a powerful tool for the fabrication of supramolecular soft materials for organic electronics and bioelectronics. Herein, we introduced the benchmark organic semiconductor [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) within the structure of a self-assembling amphipathic peptide. The molecular structure of the conjugate was rationally designed to favour π-π stacking between BTBT cores and π-delocalization within the self-assembled architectures. Hydrogels with fibrillar structure were obtained upon self-assembly. Spectroscopic studies confirmed that both hydrogen bonding between peptide segments and π-π stacking between BTBT chromophores are responsible for the formation of the 3D fibrillar network observed by transmission electron microscopy. The hydrogel was successfully deposited on gold interdigitated electrodes and a conductivity up to 1.6 (±0.1) × 10-5 S cm-1 was measured.

Peptide-Driven Charge-Transfer Organogels Built from Synergetic Hydrogen Bonding and Pyrene-Naphthalenediimide Donor-Acceptor Interactions.

The peptide-driven formation of charge transfer (CT) supramolecular gels featuring both directional hydrogen-bonding and donor-acceptor (D-A) complexation is reported. Our design consists of the coassembly of two dipeptide-chromophore conjugates, namely diphenylalanine (FF) dipeptide conveniently functionalized at the N-terminus with either a pyrene (Py-1, donor) or naphthalene diimide (NDI-1, acceptor). UV/Vis spectroscopy confirmed the formation of CT complexes. FTIR and 1 H NMR spectroscopy studies underlined the pivotal role of hydrogen bonding in the gelation process, and electronic paramagnetic resonance (EPR) measurements unraveled the advantage of preorganized CT supramolecular architectures for charge transport over solutions containing non-coassembled D and A molecular systems.

Photoinduced intercomponent excited-state decays in a molecular dyad made of a dinuclear rhenium(I) chromophore and a fullerene electron acceptor unit.

A novel molecular dyad, 1, made of a dinuclear {[Re2(µ-X)2(CO)6(µ-pyridazine)]} component covalently-linked to a fullerene unit by a carbocyclic molecular bridge has been prepared and its redox, spectroscopic, and photophysical properties - including pump-probe transient absorption spectroscopy in the visible and near-infrared region - have been investigated, along with those of its model species. Photoinduced, intercomponent electron transfer occurs in 1 from the thermally-equilibrated, triplet metal/ligand-to-ligand charge-transfer ((3)MLLCT) state of the dinuclear rhenium(I) subunit to the fullerene acceptor, with a time constant of about 100 ps. The so-formed triplet charge-separated state recombines in a few nanoseconds by a spin-selective process yielding, rather than the ground state, the locally-excited, triplet fullerene state, which finally decays to the ground state by intersystem crossing in about 290 ns.

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.

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=530 nm, as well as an emission band centered at about λ=574 nm, 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.

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.

A Peptide-Based Hydrogel for Adsorption of Dyes and Pharmaceuticals in Water Remediation.

The removal of dyes and pharmaceuticals from water has become a major issue in recent years due to the shortage of freshwater resources. The adsorption of these pollutants through nontoxic, easy-to-make, and environmentally friendly adsorbents has become a popular topic. In this work, a tetrapeptide-pyrene conjugate was rationally designed to form hydrogels under controlled acidic conditions. The hydrogels were thoroughly characterized, and their performance in the adsorption of various dyes and pharmaceuticals from water was investigated. The supramolecular hydrogel efficiently adsorbed methylene blue (MB) and diclofenac (DCF) from water. The effect of concentration in the adsorption efficiency was studied, and results indicated that while the adsorption of MB is governed by the availability of adsorption sites, in the case of DCF, concentration is the driving force of the process. In the case of MB, the nature of the dye-hydrogel interactions and the mechanism of the adsorption process were investigated through UV-Vis absorption spectroscopy. The studies proved how this dye is first adsorbed as a monomer, probably through electrostatic interactions; successively, at increasing concentrations as the electrostatic adsorption sites are depleted, dimerization on the hydrogel surface occurs.

Enantiopure Ti(IV) amino triphenolate complexes as NMR chiral solvating agents.

Enantiopure Ti(IV) complexes bearing pseudo-C(3) amino triphenolate ligands have been synthesized and characterized. The complexes bearing ortho phenyl groups act as (1)H NMR chiral solvating agent (CSA) for the stereochemical analysis of a series of sulfoxides. The coordination of a Lewis base coligand (sulfoxide) and the presence of aromatic rings are the key structural factors for the efficiency of the CSA.

Metal Cation Triggered Peptide Hydrogels and Their Application in Food Freshness Monitoring and Dye Adsorption.

Metal-ligand interactions have emerged as an important tool to trigger and modulate self-assembly, and to tune the properties of the final supramolecular materials. Herein, we report the metal-cation induced self-assembly of a pyrene-peptide conjugate to form hydrogels. The peptide has been rationally designed to favor the formation of ß-sheet 1D assemblies and metal coordination through the Glu side chains. We studied in detail the self-assembly process in the presence of H+, Li+, Na+, K+, Ca2+, Ni2+, Cu2+, Zn2+, Cd2+, Co2+, Fe3+, and Cr3+ and found that the morphology and mechanical properties of the hydrogels are ion-dependent. Moreover, thanks to the presence of the metal, new applications could be explored. Cu2+ metallogels could be used for amine sensing and meat freshness monitoring, while Zn2+ metallogels showed good selectivity for cationic dye adsorption and separation.

Graphene-Based Scaffolds for Regenerative Medicine.

Leading-edge regenerative medicine can take advantage of improved knowledge of key roles played, both in stem cell fate determination and in cell growth/differentiation, by mechano-transduction and other physicochemical stimuli from the tissue environment. This prompted advanced nanomaterials research to provide tissue engineers with next-generation scaffolds consisting of smart nanocomposites and/or hydrogels with nanofillers, where balanced combinations of specific matrices and nanomaterials can mediate and finely tune such stimuli and cues. In this review, we focus on graphene-based nanomaterials as, in addition to modulating nanotopography, elastic modulus and viscoelastic features of the scaffold, they can also regulate its conductivity. This feature is crucial to the determination and differentiation of some cell lineages and is of special interest to neural regenerative medicine. Hereafter we depict relevant properties of such nanofillers, illustrate how problems related to their eventual cytotoxicity are solved via enhanced synthesis, purification and derivatization protocols, and finally provide examples of successful applications in regenerative medicine on a number of tissues.

Stereoselective control by face-to-face versus edge-to-face aromatic interactions: the case of C(3)-Ti(IV) 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.

Efficient electron delocalization mediated by aromatic homoconjugation in 7,7-diphenylnorbornane derivatives.

Efficient electron delocalization by aromatic homoconjugated 7,7-diphenylnorbornane (DPN) in alternated homoconjugated-conjugated block copolymers and reference compounds is revealed by photophysical and electrochemical measurements. The synthesis of the polymers was achieved by Suzuki polycondensation reaction. Effective electron delocalization by DPN is demonstrated by the significant red shifts observed in the absorption and emission spectra and the variation of the energy band gap of the polymers and monomeric model compounds in comparison to a series of oligophenylenes used as references (p-quaterphenyl, p-terphenyl, and biphenyl). The electron delocalization is also clearly demonstrated by the lower oxidation potential measured for homoconjugated model compound in comparison to p-terphenyl. The results show that the electron delocalization caused by two homoconjugated aryl rings is comparable to the effect produced by one conjugated aryl ring.

Role of intermolecular interactions in oxygen transfer catalyzed by silsesquioxane trisilanolate vanadium(V).

The polyhedral oligomeric silsesquioxane trisilanolate vanadium(V) complex 1 efficiently catalyzes oxidations at room temperature using cumyl hydroperoxide as the terminal oxidant. Sulfoxidations and N-oxidations have been carried out yielding the corresponding products in good yields. The addition of a Lewis base as a coligand can markedly affect reactivity, stability, and chemo- and stereo-selectivity. A proposal for the intermolecular activation, using Gutmann analysis supported by MP2/TZVP calculations, is presented.

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)).

Stereoselectivity control in the Rh(I)-catalyzed conjugate additions of aryl and alkenylboronic acids to unprotected hydroxycyclopentenones.

[reaction: see text] The stereoselective Rh(I)-catalyzed conjugate addition reaction of aryl and alkenylboronic acids to unprotected 2-phenyl-4-hydroxycyclopentenone is presented. The free OH group on the substrate is responsible for the stereochemistry, which is cis for arylboronic derivatives. In the case of the alkenylboronic compounds, the stereochemistry can be tuned to either a cis (bases as additives) or trans addition (CsF as additive) without the need of protecting groups.

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.

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.

Amine triphenolate complexes: synthesis, structure and catalytic activity.

Triphenolamines are highly modular tetradentate molecules that effectively coordinate to transition metals and main group elements with podand topology. They form chiral complexes with intrinsically well defined coordination geometries controlled by the ligand, in particular by the nature of the substituents in ortho position to the phenol, which are able to influence their reactivity and stability. The metal complexes, especially Ti(iv) and V(v), have been found to be effective catalyst in polymerization reactions and oxygen transfer processes.