C60-based Multivalent Glycoporphyrins Inhibit SARS-CoV-2 Specific Interaction with the DC-SIGN Transmembrane Receptor.

Since WHO has declared the COVID-19 outbreak a global pandemic, nearly seven million deaths have been reported. This efficient spread of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is facilitated by the ability of the spike glycoprotein to bind multiple cell membrane receptors. Although ACE2 is identified as the main receptor for SARS-CoV-2, other receptors could play a role in viral entry. Among others, C-type lectins such as DC-SIGN are identified as efficient trans-receptor for SARS-CoV-2 infection, so the use of glycomimetics to inhibit the infection through the DC-SIGN blockade is an encouraging approach. In this regard, multivalent nanostructures based on glycosylated [60]fullerenes linked to a central porphyrin scaffold have been designed and tested against DC-SIGN-mediated SARS-CoV-2 infection. First results show an outstanding inhibition of the trans-infection up to 90%. In addition, a deeper understanding of nanostructure-receptor binding is achieved through microscopy techniques, high-resolution NMR experiments, Quartz Crystal Microbalance experiments, and molecular dynamic simulations.

Enhanced Thermoelectricity in Metal-[60]Fullerene-Graphene Molecular Junctions.

The thermoelectric properties of molecular junctions consisting of a metal Pt electrode contacting [60]fullerene derivatives covalently bound to a graphene electrode have been studied by using a conducting-probe atomic force microscope (c-AFM). The [60]fullerene derivatives are covalently linked to the graphene via two meta-connected phenyl rings, two para-connected phenyl rings, or a single phenyl ring. We find that the magnitude of the Seebeck coefficient is up to nine times larger than that of Au-C60-Pt molecular junctions. Moreover, the sign of the thermopower can be either positive or negative depending on the details of the binding geometry and on the local value of the Fermi energy. Our results demonstrate the potential of using graphene electrodes for controlling and enhancing the thermoelectric properties of molecular junctions and confirm the outstanding performance of [60]fullerene derivatives.

Topological and Multivalent Effects in Glycofullerene Oligomers as EBOLA Virus Inhibitors.

The synthesis of new biocompatible antiviral materials to fight against the development of multidrug resistance is being widely explored. Due to their unique globular structure and excellent properties, [60]fullerene-based antivirals are very promising bioconjugates. In this work, fullerene derivatives with different topologies and number of glycofullerene units were synthesized by using a SPAAC copper free strategy. This procedure allowed the synthesis of compounds 1-3, containing from 20 to 40 mannose units, in a very efficient manner and in short reaction times under MW irradiation. The glycoderivatives were studied in an infection assay by a pseudotyped viral particle with Ebola virus GP1. The results obtained show that these glycofullerene oligomers are efficient inhibitors of EBOV infection with IC50s in the nanomolar range. In particular, compound 3, with four glycofullerene moieties, presents an outstanding relative inhibitory potency (RIP). We propose that this high RIP value stems from the appropriate topological features that efficiently interact with DC-SIGN.

A 3D Peptide/[60]Fullerene Hybrid for Multivalent Recognition.

Fully substituted peptide/[60]fullerene hexakis-adducts offer an excellent opportunity for multivalent protein recognition. In contrast to monofunctionalized fullerene hybrids, peptide/[60]fullerene hexakis-adducts display multiple copies of a peptide in close spatial proximity and in the three dimensions of space. High affinity peptide binders for almost any target can be currently identified by in vitro evolution techniques, often providing synthetically simpler alternatives to natural ligands. However, despite the potential of peptide/[60]fullerene hexakis-adducts, these promising conjugates have not been reported to date. Here we present a synthetic strategy for the construction of 3D multivalent hybrids that are able to bind with high affinity the E-selectin. The here synthesized fully substituted peptide/[60]fullerene hybrids and their multivalent recognition of natural receptors constitute a proof of principle for their future application as functional biocompatible materials.

Multivalent Tryptophan- and Tyrosine-Containing [60]Fullerene Hexa-Adducts as Dual HIV and Enterovirus A71 Entry Inhibitors.

Unprecedented 3D hexa-adducts of [60]fullerene peripherally decorated with twelve tryptophan (Trp) or tyrosine (Tyr) residues have been synthesized. Studies on the antiviral activity of these novel compounds against HIV and EV71 reveal that they are much more potent against HIV and equally active against EV71 than the previously described dendrimer prototypes AL-385 and AL-463, which possess the same number of Trp/Tyr residues on the periphery but attached to a smaller and more flexible pentaerythritol core. These results demonstrate the relevance of the globular 3D presentation of the peripheral groups (Trp/Tyr) as well as the length of the spacer connecting them to the central core to interact with the viral envelopes, particularly in the case of HIV, and support the hypothesis that [60]fullerene can be an alternative and attractive biocompatible carbon-based scaffold for this type of highly symmetrical dendrimers. In addition, the functionalized fullerenes here described, which display twelve peripheral negatively charged indole moieties on their globular surface, define a new and versatile class of compounds with a promising potential in biomedical applications.

An Ultra-Long-Lived Triplet Excited State in Water at Room Temperature: Insights on the Molecular Design of Tridecafullerenes.

Suitably engineered molecular systems exhibiting triplet excited states with very long lifetimes are important for high-end applications in nonlinear optics, photocatalysis, or biomedicine. We report the finding of an ultra-long-lived triplet state with a mean lifetime of 93 ms in an aqueous phase at room temperature, measured for a globular tridecafullerene with a highly compact glycodendrimeric structure. A series of three tridecafullerenes bearing different glycodendrons and spacers to the C60 units have been synthesized and characterized. UV/Vis spectra and DLS experiments confirm their aggregation in water. Steady-state and time-resolved fluorescence experiments suggest a different degree of inner solvation of the multifullerenes depending on their molecular design. Efficient quenching of the triplet states by O2 but not by waterborne azide anions has been observed. Molecular modelling reveals dissimilar access of the aqueous phase to the internal structure of the tridecafullerenes, differently shielded by the glycodendrimeric shell.

Synthesis of Highly Efficient Multivalent Disaccharide/[60]Fullerene Nanoballs for Emergent Viruses.

After the last epidemic of the Zika virus (ZIKV) in Brazil that peaked in 2016, growing evidence has been demonstrated of the link between this teratogenic flavivirus and microcephaly cases. However, no vaccine or antiviral drug has been approved yet. ZIKV and Dengue viruses (DENV) entry to the host cell takes place through several receptors, including dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), so that the blockade of this receptor through multivalent glycoconjugates supposes a promising biological target to inhibit the infection process. In order to get enhanced multivalency in biocompatible systems, tridecafullerenes appended with up to 360 1,2-mannobiosides have been synthesized using a strain-promoted cycloaddition of azides to alkynes (SPAAC) strategy. These systems have been tested against ZIKV and DENV infection, showing an outstanding activity in the picomolar range.

Nanocarbon-Based Glycoconjugates as Multivalent Inhibitors of Ebola Virus Infection.

SWCNTs, MWCNTs, and SWCNHs have been employed as virus-mimicking nanocarbon platforms for the multivalent presentation of carbohydrates in an artificial Ebola virus infection model assay. These carbon nanoforms have been chemically modified by the covalent attachment of glycodendrons and glycofullerenes using the CuAAC "click chemistry" approach. This modification dramatically increases the water solubility of these structurally different nanocarbons. Their efficiency in blocking DC-SIGN-mediated viral infection by an artificial Ebola virus has been tested in a cellular experimental assay, finding that glycoconjugates based on MWCNTs functionalized with glycofullerenes are potent inhibitors of viral infection.

Maleimide and Cyclooctyne-Based Hexakis-Adducts of Fullerene: Multivalent Scaffolds for Copper-Free Click Chemistry on Fullerenes.

The synthesis of multivalent systems based on hexakis-adducts of [60]fullerene employing a biocompatible copper-free click chemistry strategy has been accomplished. A symmetric hexakis-adduct of fullerene bearing 12 maleimide units (3) is reported, and it has been employed to carry out the thiol-maleimide Michael addition. To achieve orthogonal click addition, an asymmetric derivative bearing one maleimide and 10 cyclooctynes has been synthesized. The sequential and one-pot transformations of the two clickable groups have been explored, finding the best results in the case of the one-pot experiment. This route has been used to obtain a biocompatible hexakis-adduct appended with two different biomolecules, carbohydrates, and amino acids.

Multivalent Glycosylated Nanostructures To Inhibit Ebola Virus Infection.

The infection of humans by lethal pathogens such as Ebola and other related viruses has not been properly addressed so far. In this context, a relevant question arises: What can chemistry do in the search for new strategies and approaches to solve this emergent problem? Although initially a variety of known chemical compounds-for other purposes-proved disappointing in tests against Ebola virus (EBOV) infection, more recently, specific molecules have been prepared. In this Perspective, we present new approaches directed at the design of efficient entry inhibitors to minimize the development of resistance by viral mutations. In particular, we focus on dendrimers as well as fullerene C60-with a unique symmetrical and 3D globular structure-as biocompatible carbon platforms for the multivalent presentation of carbohydrates. The antiviral activity of these compounds in an Ebola pseudotyped infection model was in the low micromolar range for fullerenes with 12 and 36 mannoses. However, new tridecafullerenes-in which the central alkyne scaffold of [60]fullerene is connected to 12 sugar-containing [60]fullerene units (total 120 mannoses)-exhibit an outstanding antiviral activity with IC50 in the sub-nanomolar range! The multivalent presentation of specific carbohydrates by using 3D fullerenes as controlled biocompatible carbon scaffolds represents a real advance, being currently the most efficient molecules in vitro against EBOV infection. However, additional studies are needed to determine the optimized fullerene-based leads for practical applications.

Hexakis [60]Fullerene Adduct-Mediated Covalent Assembly of Ruthenium Nanoparticles and Their Catalytic Properties.

The C66 (COOH)12 hexa-adduct has been successfully used as a building block to construct carboxylate bridged 3D networks with very homogeneous sub-1.8 nm ruthenium nanoparticles. The obtained nanostructures are active in nitrobenzene selective hydrogenation.

Supramolecular Complexation of Carbon Nanostructures by Crown Ethers.

Since their discovery, crown ethers as well as the most recent carbon nanostructures, namely fullerenes, carbon nanotubes, and graphene, have received a lot of attention from the chemical community. Merging these singular chemical structures by noncovalent forces has provided a large number of unprecedented supramolecular assemblies with new geometric and electronic properties whose more representative examples are presented in this Synopsis organized according to the different nature of the carbon nanostructures.

Conjugated Porphyrin Dimers: Cooperative Effects and Electronic Communication in Supramolecular Ensembles with C60.

Two new conjugated porphyrin-based systems (dimers 3 and 4) endowed with suitable crown ethers have been synthesized as receptors for a fullerene-ammonium salt derivative (1). Association constants in solution have been determined by UV-vis titration experiments in CH2Cl2 at room temperature. The designed hosts are able to associate up to two fullerene-based guest molecules and present association constants as high as ∼5 × 108 M-1. Calculation of the allosteric cooperative factor α for supramolecular complexes [3·12] and [4·12] showed a negative cooperative effect in both cases. The interactions accounting for the formation of the associates are based, first, on the complementary ammonium-crown ether interaction and, second, on the π-π interactions between the porphyrin rings and the C60 moieties. Theoretical calculations have evidenced a significant decrease of the electron density in the porphyrin dimers 3 and 4 upon complexation of the first C60 molecule, in good agreement with the negative cooperativity found in these systems. This negative effect is partially compensated by the stabilizing C60-C60 interactions that take place in the more stable syn-disposition of [4·12].

Investigation of glycofullerene dynamics by NMR spectroscopy.

Glycofullerenes, in which carbohydrate molecules are attached via a linker to a [60]fullerene core, facilitate spherical presentation of glyco-based epitopes. We herein investigate the dynamics of two glycofullerenes, having 12 and 36 mannose residues at their periphery, by NMR translational diffusion and quantitative (13)C relaxation studies employing a model-free approach for their interpretation. The sugar residues are shown to be highly flexible entities with S(2) < 0.2 in both compounds. Notably, the larger glycofullerene with longer linkers shows faster internal dynamics and higher flexibility than its smaller counterpart. The dynamics and flexibility as well as the slower translational diffusion of the larger glycofullerene, thereby favoring rebinding to a receptor, may together with its spatial extension explain why it is better than the smaller one at blocking the DC-SIGN receptor and inhibiting the infection by pseudotyped Ebola virus particles.

Metal-atom impact on the self-assembly of cup-and-ball metalloporphyrin-fullerene conjugates.

A fullerene ammonium derivative has been combined with different metalloporphyrin-crown ether receptors to generate very stable supramolecules. The combination of fullerene-porphyrin and ammonium-crown ether interactions leads to a strong chelate effect as evidenced by a high effective molarity (3.16 M). The different parameters influencing the stability of the supramolecular ensembles, in particular the nature of the metal in the porphyrin moiety, have been rationalized with the help of theoretical calculations thus providing new insights into fullerene-porphyrin interactions.

Glycofullerenes inhibit viral infection.

Water-soluble glycofullerenes based on a hexakis-adduct of [60]fullerene with an octahedral addition pattern are very attractive compounds providing a spherical presentation of carbohydrates. These tools have been recently described and they have been used to interact with lectins in a multivalent manner. Here, we present the use of these glycofullerenes, including new members with 36 mannoses, as compounds able to inhibit a DC-SIGN-dependent cell infection by pseudotyped viral particles. The results obtained in these experiments demonstrate for the first time that these glycoconjugates are adequate to inhibit efficiently an infection process, and therefore, they can be considered as very promising and interesting tools to interfere in biological events where lectins such as DC-SIGN are involved.

Nanorods versus nanovesicles from amphiphilic dendrofullerenes.

Three new amphiphilic dendrofullerenes endowed with 4, 8, and 16 carboxylic groups have been efficiently prepared by using a click chemistry methodology. These amphiphilic fullerene derivatives aggregate forming micelles, nanorods, or hollow vesicles depending on the concentration and on the solid substrate.

A fully conjugated TTF-π-TCAQ system: synthesis, structure, and electronic properties.

The synthesis of the first fully conjugated tetrathiafulvalene-tetracyano-p-quinodimethane ((TTF)-TCNQ)-type system has been carried out by means of a Julia-Kocienski olefination reaction. In particular, a tetracyanoanthraquinodimethane (TCAQ) formyl derivative and two new sulfonylmethyl-exTTFs (exTTF = 2-[9-(1,3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole)--prepared as new building blocks--were linked. A variety of experimental conditions reveal that the use of sodium hexamethyldisilazane (NaHMDS) as base in THF afforded the E olefins with excellent stereoselectivity. Theoretical calculations at the B3LYP/6-31G** level point to highly distorted exTTF and TCAQ that form an almost planar stilbene unit between them. Although calculations predicted appreciable electronic communication between the donor and the acceptor, cyclic voltammetric studies did not substantiate this effect. It was only in photophysical assays that the electronic communication emerged in the form of a charge-transfer (CT) absorption and emission. Once photoexcited (i.e., the locally excited state or excited charge-transfer state), an ultrafast, subpicosecond charge separation leads to a radical ion pair state in which the spectroscopic features of the radical cation of exTTF as well as the radical anion of TCAQ are discernable. The radical ion pair is metastable and undergoes a fast ((1.0±0.2) ps) charge recombination to reconstitute the electronic ground state. Such ultrafast charge separation and recombination processes come as a consequence of the very short vinyl linkage between the two electroactive units.

A new exTTF-crown ether platform to associate fullerenes: cooperative n-π and π-π effects.

A new and readily available exTTF-bis(crown ether), 1, efficiently recognizes C60 as well as C70 by means of cooperative π-π and n-π interactions. The geometrical (concave-convex) and electronic (donor-acceptor) complementarity accounts on one hand for remarkable binding strengths, with association constants reaching 10(7) M(-1) in benzonitrile, and on the other hand for lifetimes of the photogenerated radical ion pair state on the order of 45 ps.

Multivalent cationic dendrofullerenes for gene transfer: synthesis and DNA complexation.

Non-viral nucleic acid vectors able to display high transfection efficiencies with low toxicity and overcoming the multiple biological barriers are needed to further develop the clinical applications of gene therapy. The synthesis of hexakis-adducts of [60]fullerene endowed with 12, 24 and 36 positive ammonium groups and a tridecafullerene appended with 120 positive charges has been performed. The delivery of a plasmid containing the green fluorescent protein (EGFP) gene into HEK293 (Human Embryonic Kidney) cells resulting in effective gene expression has demonstrated the efficacy of these compounds to form polyplexes with DNA. Particularly, giant tridecafullerene macromolecules have shown higher efficiency in the complexation and transfection of DNA. Thus, they can be considered as promising non-viral vectors for transfection purposes.