No abstract

The lack of solubility in water and the formation of aggregates hamper many opportunities for technological exploitation of C60. Here, different peptides were designed and synthesized with the aim of monomolecular dispersion of C60 in water. Phenylalanines were used as recognizing moieties, able to interact with C60 through π–π stacking, while a varying number of glycines were used as spacers, to connect the two terminal phenylalanines. The best performance in the dispersion of C60 was obtained with the FGGGF peptidic nanotweezer at a pH of 12. A full characterization of this adduct was carried out. The peptides disperse C60 in water with high efficiency, and the solutions are stable for months both in pure water and in physiological environments. NMR measurements demonstrated the ability of the peptides to interact with C60. AFM measurements showed that C60 is monodispersed. Electrospray ionization mass spectrometry determined a stoichiometry of C60@(FGGGF)4. Molecular dynamics simulations showed that the peptides assemble around the C60 cage, like a candy in its paper wrapper, creating a supramolecular host able to accept C60 in the cavity. The peptide-wrapped C60 is fully biocompatible and the C60 “dark toxicity” is eliminated. C60@(FGGGF)4 shows visible light-induced reactive oxygen species (ROS) generation at physiological saline concentrations and reduction of the HeLa cell viability in response to visible light irradiation.

Of all the amino acids, the surface of π‐electron conjugated carbon nanoparticles has the largest affinity for tryptophan, followed by tyrosine, phenylalanine, and histidine. In order to increase the binding of a protein to a fullerene, it should suffice to mutate a residue of the site that binds to the fullerene to tryptophan, Trp. Computational chemistry shows that this intuitive approach is fraught with danger. Mutation of a binding residue to Trp may even destabilize the binding because of the complicated balance between van der Waals, polar and non‐polar solvation interactions.

Lysine-modified graphene oxide is synthesized and exploited as an adsorbent of emerging contaminants in drinking water.

No abstract

We carried out a computational investigation on the mechanism of the bromination reaction of N-phenylacetamide inside CNTs, in water, and in an aprotic solvent (ethylbenzene). A full QM and a QM/MM approach was used. In the aprotic solvent, a Wheland intermediate (ion pair formed by arenium ion and chloride) exists only for the attack in the ortho position, while the para attack proceeds in a concerted manner (concerted direct substitution). The reaction is catalyzed by the HCl byproduct, which lowers significantly the activation barriers. The ortho product is favored, in contrast to the common belief based on simple steric effects. In water solution a Wheland intermediate was located for both ortho and para attacks (the ion pair is stabilized by the polar protic solvent). The formation of the para product is favored with respect to the ortho product: 9.0 and 9.9 kcal mol–1 are the corresponding activation barriers. Inside CNTs, as found in aprotic solvent, the Wheland-type arenium ion exists only along the ortho pathway. The initial production of the HCl byproduct activates rapidly the catalyzed mechanism that proceeds almost exclusively along the para pathway (para and ortho activation barriers are 6.1 and 17.0 kcal mol–1, respectively). The almost exclusive para regioselectivity for the CNT-confined reaction and its acceleration with respect to water (in agreement with the experimental evidence) are due to noncovalent (van der Waals) interactions between the endohedral system and the electron cloud of the surrounding CNT. The effect of these interactions was estimated quantitatively within the UFF scheme used in our QM/MM computations, and we found that they are particularly stabilizing for the para-catalyzed process.

Extraction of proteins from blood biological fluids requires the removal of large aggregates or cells by membrane filtration. However, conventional filters, based on simple size exclusion, do not allow to...

LAC (hydroxylactone (1R,5S)-1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one) is one of the most interesting products of the pyrolysis of cellulose and represents a useful chiral building block in organic synthesis. A computational investigation at the DFT level on the mechanism of formation of LAC shows that this species can be obtained following two reaction paths, path A and path B, starting from a well-known pyrolysis product (ascopyrone P). A series of internal rearrangements involving in all cases a proton transfer leads directly to LAC (path B). An alternative path (path A) can be also followed. From this path, via a "gate" connecting the two reaction channels, it is possible to reach path B and form LAC. In both cases, the rate-determining step of the process is the initial keto-enol isomerization. We found that water, which is present in the reaction mixture, "catalyzes" the reaction by assisting the proton transfers present in all the steps of the process. In particular, water lowers the barrier of the rate-determining step that becomes 40.9 kcal mol (79.4 kcal mol in the absence of water). The corresponding computed rate constant is 4.3×10 s at 500 °C, a value which is consistent with the presence of LAC in the absence of metal catalysts. The results of this study on the non-catalyzed process underpin the important role played by water in the formation of pyrolysis products of cellulose where proton transfer is a key mechanistic step.