Expanding the Chemical Space of Tetracyanobuta-1,3-diene (TCBD) through a Cyano-Diels-Alder Reaction: Synthesis, Structure, and Physicochemical Properties of an Anthryl-fused-TCBD Derivative

Tetracyanobuta-1,3-diene (TCBD) is a powerful and versatile electron-acceptor moiety widely used for the preparation of electroactive conjugates. While many reports addressing its electron-accepting capability have appeared in the literature, significantly scarcer are those dealing with its chemical modification, a relevant topic which allows to broaden the chemical space of this interesting functional unit. Here, we report on the first example of a high-yielding cyano-Diels-Alder (CDA) reaction between TCBD, that is, where a nitrile group acts as a dienophile, and an anthryl moiety, that is, acting as a diene. The resulting anthryl-fused-TCBD derivative, which structure was unambiguously identified by X-ray diffraction, shows high thermal stability, remarkable electron-accepting capability, and interesting electronic ground- and excited-state features, as characterized by a thorough theoretical, electrochemical, and photophysical investigation. Moreover, a detailed kinetic analysis of the intramolecular CDA reaction transforming the anthryl-TCBD-based reactant into the anthryl-fused-TCBD product was carried out at different temperatures

One-step functionalization of mildly and strongly reduced graphene oxide with maleimide: An experimental and theoretical investigation of the Diels-Alder [4+2] cycloaddition reaction

For large-scale graphene applications, such as the production of polymer-graphene nanocomposites, exfoliated graphene oxide (GO) and its reduced form (rGO) are presently considered to be very suitable starting materials, showing enhanced chemical reactivity with respect to pristine graphene, in addition to suitable electronic properties (i.e., tunable band gap). Among other chemical processes, a suitable way to obtain surface decoration of graphene is through a direct one-step Diels-Alder (DA) reaction, e.g. through the use of dienophile or diene moieties. However, the feasibility and extent of decoration largely depends on the specific graphene microstructure that in the case of rGO sheets is not easy to control and generally presents a high degree of inhomogeneity owing to various on-plane functionalization (e.g., epoxide and hydroxyl groups) or in-plane lattice defects. In an effort to gain some insights into the covalent functionalization of variably reduced GO samples, we present a combined experimental and theoretical study on the DA cycloaddition reaction of maleimide, a dienophile functional unit well-suited for chemical conjugation of polymers and macromolecules. In particular, we considered both mildly and strongly reduced GOs. Using thermogravimetry, Raman and X-Ray photoelectron spectroscopy, and elemental analysis we show evidence of variable chemical reactivity of rGO as a function of the residual oxygen content. Moreover, from quantum mechanical calculations carried out at the DFT level on different graphene reaction sites, we provide a more detailed molecular view to interpret experimental findings and to assess the reactivity series of different graphene modifications. This journal i

Photoinduced azobenzene-modified DNA dehybridization: Insights into local and cooperativity effects from a molecular dynamics study

Photoresponsive azobenzene-modified DNA (RNA) has become a very fruitful material for nanotechnology due to the capability of switching on and off hybridization (i.e., duplex formation) in smart nanostructures. This nanomaterial exploits the well-known azobenzene trans/cis photo-isomerization. In fact, it has been found that DNA tethered with trans-azobenzene shows normal nucleic acid recognition and hybridization, while the cis form destabilizes the duplex configuration, eventually leading to DNA unzipping. However, while the working principle of the light-triggered DNA dehybridization is apparent, specific details of this mechanism still remain elusive to experiments. Previous in silico studies successfully addressed some aspects (e.g., local structural effects, thermal stability, and early events of azobenzene photoisomerization) of this challenging molecular process characterized by timescales spanning several orders of magnitude, from picoseconds (i.e., azobenzene photoisomerization) to micro- and milli-seconds (i.e., complete strand detachment). In this work, inspired by a recent report by Asanuma and coworkers, we focus on the local and cooperativity effects played by multiple azobenzene units on a 10-mer azobenzene-modified DNA duplex. Using molecular dynamics (MD) simulations, we investigated nine systems equipped with a variable number (from 1 to 7) of photoswitch units and different configurations, focusing our analysis on the initial events (from few ps to hundreds of ns) characterizing DNA destabilization upon trans-to-cis isomerization, such as hydrogen bonding breakage and base pair misalignment. Results highlight, on one hand, the local effects of single azobenzene units on DNA duplex structure and, on the other hand, the cooperative role that multiple photoswitches show in enhancing and accelerating DNA dehybridization following trans-to-cis conversion, in agreement with previously reported data and observations

Temperature Dependence of the Structure and Dynamics of a Dye-Labeled Lipid in a Planar Phospholipid Bilayer: A Computational Study

Fluorescent probes are widely employed to label lipids for the investigation of structural and dynamic properties of model and cell membranes through optical microscopy techniques. Although the effect of tagging a lipid with an organic dye is generally assumed to be negligible, optically modified lipids can nonetheless affect the local lipid structure and, in turn, the lipid lateral mobility. To better assess this potential issue, all-atom (MD) molecular dynamics simulations have been performed to study structural and dynamic effects in a model DOPC membrane in the presence of a standard Rhodamine B-labeled DOPE lipid (RHB) as a function of temperature, i.e., 293 K, 303 K, and 320 K. As the temperature is increased, we observe similar changes in the structural properties of both pure DOPC and RHB-DOPC lipid bilayers: an increase of the area per lipid, a reduction of the membrane thickness and a decrease of lipid order parameters. The partial density profile of the RHB headgroups and their orientation within the lipid bilayer confirm the amphiphilic nature of the RHB fluorescent moiety, which mainly partitions in the DOPC glycerol backbone region at each temperature. Moreover, at all temperatures, our results on lipid lateral diffusion support a non-neutral role of the dye with respect to the unlabeled lipid mobility, thus suggesting important implications for optical microscopy studies of lipid membranes