Sequential Copper-Catalyzed Alkyne–Azide Cycloaddition and Thiol-Maleimide Addition for the Synthesis of Photo- and/or Electroactive Fullerodendrimers and Cysteine-Functionalized Fullerene Derivatives

Clicked BODIPY-Fullerene-Peptide Assemblies: Studies of Electron Transfer Processes in Self-Assembled Monolayers on Gold Surfaces

Two BODIPY-C60-peptide assemblies were synthesized by CuAAC reactions of BODIPY-C60 dyads and a helical peptide functionalized with a terminal alkyne group and an azide group, respectively. The helical peptide within these assemblies was functionalized at its other end by a disulfide group, allowing formation of self-assembled monolayers (SAMs) on gold surfaces. Characterizations of these SAMs, as well as those of reference molecules (BODIPY-C60-alkyl, C60-peptide and BODIPY-peptide), were carried out by PM-IRRAS and cyclic voltammetry. BODIPY-C60-peptide SAMs are more densely packed than BODIPY-C60-alkyl and BODIPY-peptide based SAMs. These findings were attributed to the rigid peptide helical conformation along with peptide-peptide and C60-C60 interactions within the monolayers. However, less dense monolayers were obtained with the target assemblies compared to the C60-peptide, as the BODIPY entity likely disrupts organization within the monolayers. Finally, electron transfer kinetics measurements by ultra-fast electrochemistry experiments demonstrated that the helical peptide is a better electron mediator in comparison to alkyl chains. This property was exploited along with those of the BODIPY-C60 dyads in a photo-current generation experiment by converting the resulting excited and/or charge separated states from photo-illumination of the dyad into electrical energy.

Controlled Decoration of [60]Fullerene with Polymannan Analogues and Amino Acid Derivatives through Malondiamide-Based Linkers

In the last few years, nanomaterials based on fullerene have begun to be considered promising tools in the development of efficient adjuvant/delivery systems for vaccination, thanks to their several advantages such as biocompatibility, size, and easy preparation and modification. In this work we reported the chemoenzymatic synthesis of natural polymannan analogues (di- and tri-mannan oligosaccharides characterized by α1,6man and/or α1,2man motifs) endowed with an anomeric propargyl group. These sugar derivatives were submitted to 1,3 Huisgen dipolar cycloaddition with a malondiamide-based chain equipped with two azido terminal groups. The obtained sugar-modified malondiamide derivatives were used to functionalize the surface of Buckminster fullerene (C₆₀) in a highly controlled fashion, and yields (11–41%) higher than those so far reported by employing analogue linkers. The same strategy has been exploited to obtain C₆₀ endowed with natural and unnatural amino acid derivatives. Finally, the first double functionalization of fullerene with both sugar- and amino acid-modified malondiamide chains was successfully performed, paving the way to the possible derivatization of fullerenes with immunogenic sugars and more complex antigenic peptides.

Photoinduced Electron Transfer and Energy Transfer Processes in a Flexible BODIPY-C60 Dyad

A new donor-acceptor dyad composed of a BODIPY (4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene) donor and a fullerene C₆₀ acceptor has been synthesized and characterized. This derivative has been prepared using a clickable fullerene building block that bears an alkyne moiety and a maleimide unit. The post-functionalization of the maleimide group by a BODIPY thiol leads to a BODIPY-C₆₀ dyad, leaving the alkyne moiety for further functional arrangement. On the basis of the combination of semi-empirical and density functional theory (DFT) calculations, spectroelectrochemical experiments, and steady-state and time-resolved spectroscopies, the photophysical properties of this new BODIPY-C₆₀ dyad were thoroughly studied. By using semi-empirical calculations, the equilibrium of three conformations of the BODIPY-C₆₀ dyad has been deduced, and their molecular orbital structures have been analyzed using DFT calculations. Two short fluorescence lifetimes were attributed to two extended conformers displaying variable donor-acceptor distances (17.5 and 20.0 Å). Additionally, the driving force for photoinduced electron transfer from the singlet excited state of BODIPY to the C₆₀ moiety was calculated using redox potentials determined with electrochemical studies. Spectroelectrochemical measurements were also carried out to investigate the absorption profiles of radicals in the BODIPY-C₆₀ dyad in order to assign the transient species in pump-probe experiments. Under selective photoexcitation of the BODIPY moiety, occurrences of both energy and electron transfers were demonstrated for the dyad by femtosecond and nanosecond transient absorption spectroscopies. Photoinduced electron transfer occurs in the folded conformer, while energy transfer is observed in extended conformers.

Peptide-Based Multiepitopic Vaccine Platforms via Click Reactions

Multimeric antigen display and high overall valency are increasingly regarded as strategic goals for potent and broadly efficacious synthetic vaccines with potential market prospects. Herein, a modular and versatile approach to multifunctional peptide-based vaccine platforms at multimilligram scale in reasonable yields is reported. Preparation of chemoselectively modified peptide building blocks of medium-to-large size, conjugation of these subunits, and final assembly were achieved by a combination of Michael-type thiol-ene addition and copper(I)-mediated alkyne-azide cycloaddition. The size and structural complexity of the building blocks required exploration of a further level of orthogonality, namely furan/maleimide Diels-Alder chemistry. After process optimization, a finely tuned, stepwise click approach has emerged as a workable, on-demand strategy to create macromolecular therapeutic vaccine assemblies.

A fullerene helical peptide: synthesis, characterization and formation of self-assembled monolayers on gold surfaces

A helical C60-peptide allowed the formation of well-packed SAMs compared to a C60-alkyl peptide, which was determined by QCM and CV experiments.