Growth of carbon nanotubes on metal nanoparticles: a microscopic mechanism from ab initio molecular dynamics simulations

We report on ab initio molecular dynamics simulations of the early stages of single-walled carbon nanotube (SWCNT) growth on metal nanoparticles. Our results show that a sp2 bonded cap is formed on an iron catalyst, following the diffusion of C atoms from hydrocarbon precursors on the nanoparticle surface. The weak adhesion between the cap and iron enables the graphene sheet to "float" on the curved surface, as additional C atoms covalently bonded to the catalyst "hold" the tube walls. Hence the SWCNT grows capped. At the nanoscale, we did not observe any tendency of C atoms to penetrate inside the catalyst, consistent with total energy calculations showing that alloying of Fe and C is very unlikely for 1 nm particles. Root growth was observed on Fe but not on Au, consistent with experiment.     

Preliminary Study on New Alternative Binders through Re-Refined Engine Oil Bottoms (REOBs) and Industrial By-Product Additives

Recent studies have worked towards addressing environmental issues such as global warming and greenhouse gas emissions due to the increasing awareness of the depletion of natural resources. The asphalt industry is seeking to implement measures to reduce its carbon footprint and to promote sustainable operations. The reuse of several wastes and by-products is an example of a more eco-friendly activity that fulfils the circular economy principle. Among all possible solutions, the road pavement sector encourages, on one hand, the use of recycled materials as a partial replacement of the virgin lithic skeleton; on the other hand, it promotes the use of recycled materials to substituting for a portion of the petroleum bituminous binder. This study aims to use Re-refined Engine Oil Bottoms (REOBs) as a main substitute and additives from various industrial by-products as a full replacement for virgin bitumen, producing high-performing alternative binders. The REOBs have been improved by utilizing additives in an attempt to improve their specific properties and thus to bridge the gap between REOBs and traditional bituminous binders. An even larger amount of virgin and non-renewable resources can be saved using these new potential alternative binders together with the RAP aggregates. Thus, the reduction in the use of virgin materials is applied at the binder and the asphalt mixture levels. Rheological, spectroscopic, thermogravimetric, and mechanical analysis were used to characterize the properties, composition, and characteristics of the REOBs, REOB-modified binders, and asphalt mixes. Thanks to the rheological investigations of possible alternative binders, 18 blends were selected, since they behaved like an SBS-modified bitumen, and then they were used for producing the corresponding asphalt mixtures. The preliminary mechanical analysis of the asphalt mixtures shows that six mixes have promising responses in terms of stiffness, tensile resistance, and water susceptibility. Nevertheless, the high variability of recycled materials and by-products has to be taken into consideration during the definition of alternative binders and recycled asphalt mixtures. In fact, this study highlights the crucial effects of the chemical composition of the constituents and their compatibility on the behaviour of the final product. This preliminary study represents a first attempt to define alternative binders, which can be used in combination with recycled aggregates for producing more sustainable road materials. However, further analysis is necessary in order to assess the durability and the ageing tendency of the materials.     

Nanoscale Platelet Formation by Monounsaturated and Saturated Sophorolipids under Basic pH Conditions

The self‐assembly behavior of the yeast‐derived bolaamphiphile sophorolipid (SL) is generally studied under acidic/neutral pH conditions, at which micellar and fibrillar aggregates are commonly found, according to the (un)saturation of the aliphatic chain: the cis form, which corresponds to the oleic acid form of SL, spontaneously forms micelles, whereas the saturated form, which corresponds to the stearic acid form of SL, preferentially forms chiral fibers. By using small‐angle light and X‐ray scattering (SLS, SAXS) combined with high‐sensitivity transmission electron microscopy imaging under cryogenic conditions (cryo‐TEM), the nature of the self‐assembled structures formed by these two compounds above pH 10, which is the pH at which they are negatively charged due to the presence of a carboxylate group, has been explored. Under these conditions, these compounds self‐assemble into nanoscale platelets, despite the different molecular structures. This work shows that the electrostatic repulsion forces generated by COO^? mainly drive the self‐assembly process at basic pH, in contrast with that found at pH below neutrality, at which self‐assembly is driven by van der Waals forces and hydrogen bonding, and thus, is in agreement with previous findings on carbohydrate‐based gemini surfactants.     

Structural events in the photocycle of green fluorescent protein

Picosecond time-resolved mid-infrared absorption changes of the wild type green fluorescent protein from Aequorea victoria are reported on structural events during the photocycle. Concomitant with rapid H/D transfer following excitation of the neutral A state at 400 nm, a transient signal at 1721/1711 cm(-1) (H/D) developed belonging to protonated glutamate 222, which was definitively assigned using the E222D mutant from the altered proton-transfer kinetics to aspartate in addition to the altered band position and intensity in the spectra. A transient at 1697 cm(-1), assigned to a structural perturbation of glutamine 69, had a H/D kinetic isotope effect of >32, showing the conformational dynamics to be sensitive to the active site H/D vibrations. The kinetic data up to 2 ns after excitation in the 1250-1800 cm(-1) region in D2O provided 10 and 75 ps time constants for the excited-state deuteron transfer and the associated A1* - A1 and A2* - A2 difference spectra and showed the radiative intermediate I state vibrations and the transient accumulation of the long-lived ground-state intermediate I2. Assignments of chromophore modes for the A1, A2, and I2 ground states are proposed on the basis of published model compound studies (Esposito, A. P.; Schellenberg, P.; Parson, W. W.; Reid, P. J. J. Mol. Struct. 2001, 569, 25 and He, X.; Bell, A. F.; Tonge, P. J. J. Phys. Chem. B 2002, 106, 6056). Tentative assignments for the singlet-state intermediates A1*, A2*, and I* are discussed. An unexpected and unassigned band that may be a C=C chromophore vibration was observed in the ground state (1665 cm(-1)) as well as in all photocycle intermediates. Optical dumping of the transient I population was achieved using an additional 532 nm pulse and the directly obtained I2 - I* difference spectrum was highly similar to the I2 - I* photocycle spectrum. The pump-dump-probe spectrum differed from the pump-probe photocycle difference spectrum with respect to the intensity of the phenol 1 mode at 1578 cm(-1), suggesting stronger delocalization of the negative charge onto the phenolic ring of the anionic chromophore in the dumped I2 state. Indication for structural heterogeneity of the chromophore, Glu 222, and the chromophore environment was found in the two parallel proton-transfer reactions and their distinct associated ground- and intermediate-state vibrations. Vibrational spectral markers at 1695 cm(-1) assigned to Gln 69, at 1631 cm(-1) belonging to a C=C mode, and at 1354 cm(-1) belonging to a phenolate vibration further indicated the I2 and I* states to be unrelaxed.     

The synthesis and conformation of oxygenated trianglimine macrocycles

The synthesis of series of D(2h) and C(2v) symmetric oxygenated aromatic dicarboxaldehydes, using dilithiation methodology, is described along with their reactivity in the [3+3] cyclocondensation reaction with (1R,2R)-diaminocyclohexane to give oxygenated trianglimine macrocycles. Macrocycles derived from C(2v) symmetric dialdehydes give macrocycles with a stereogenic aromatic plane with complete diastereocontrol, as a mixture of rotamers.     

Generalized Control Systems in the Space of Probability Measures

In this paper we formulate a time-optimal control problem in the space of probability measures. The main motivation is to face situations in finite-dimensional control systems evolving deterministically where the initial position of the controlled particle is not exactly known, but can be expressed by a probability measure on \(\mathbb {R}^{d}\). We propose for this problem a generalized version of some concepts from classical control theory in finite dimensional systems (namely, target set, dynamic, minimum time function...) and formulate an Hamilton-Jacobi-Bellman equation in the space of probability measures solved by the generalized minimum time function, by extending a concept of approximate viscosity sub/superdifferential in the space of probability measures, originally introduced by Cardaliaguet-Quincampoix in Cardaliaguet and Quincampoix (Int. Game Theor. Rev. 10, 1–16, 2008). We prove also some representation results linking the classical concept to the corresponding generalized ones. The main tool used is a superposition principle, proved by Ambrosio, Gigli and Savaré in Ambrosio et al. [3], which provides a probabilistic representation of the solution of the continuity equation as a weighted superposition of absolutely continuous solutions of the characteristic system.     

Combining Solid-State NMR with Structural and Biophysical Techniques to Design Challenging Protein-Drug Conjugates

Several protein-drug conjugates are currently being used in cancer therapy. These conjugates rely on cytotoxic organic compounds that are covalently attached to the carrier proteins or that interact with them via non-covalent interactions. Human transthyretin (TTR), a physiological protein, has already been identified as a possible carrier protein for the delivery of cytotoxic drugs. Here we show the structure-guided development of a new stable cytotoxic molecule based on a known strong binder of TTR and a well-established anticancer drug. This example is used to demonstrate the importance of the integration of multiple biophysical and structural techniques, encompassing microscale thermophoresis, X-ray crystallography and NMR. In particular, we show that solid-state NMR has the ability to reveal effects caused by ligand binding which are more easily relatable to structural and dynamical alterations that impact the stability of macromolecular complexes.     

Cyclic Olefin Copolymer Interleaves for Thermally Mendable Carbon/Epoxy Laminates

Thin cyclic olefin copolymer (COC) foils were used as intrinsic thermoplastic healing agents in carbon fiber (CF)-reinforced epoxy laminates. COC films were produced by hot pressing and were interleaved in the interlaminar regions between each EP/CF lamina, during the hand layup fabrication of the laminates. Three samples were produced, i.e., the neat EP/CF laminate without COC, and two laminates containing COC layers with a thickness of 44 μm and 77 μm, respectively. It was observed that the fiber volume fraction decreased, and the porosity increased with the introduction of COC layers, and this effect was more evident when thick films were used. These two effects, combined with the sub-optimal adhesion between COC and EP, caused a decrease in the mechanical properties (i.e., the elastic modulus, flexural strength, interlaminar shear strength and interlaminar fracture toughness) of the laminates. Specimens subjected to mode I interlaminar fracture toughness test were then thermally mended under pressure by resistive heating, through the Joule effect of conductive CFs. A temperature of approximately 190 °C was reached during the healing treatment. The healing efficiency was evaluated as the ratio of critical strain energy release rate (G_IC) of the healed and virgin specimens. Healed specimens containing COC layers of 44 μm and 77 μm exhibited a healing efficiency of 164% and 100%, respectively. As expected, the healing treatment was not beneficial for the neat EP/CF laminate without COC, which experienced a healing efficiency of only 2%. This result proved the efficacy of COC layers as a healing agent for EP/CF laminates, and the effectiveness of resistive heating as a way to activate the intrinsic healing mechanism.