Coloured Jones invariants of links and the Volume Conjecture

We extend the definition of the coloured Jones polynomials toframed links and trivalent graphs in S³# k (S² x S¹) using astate-sum formulation based on Turaev's shadows. Then, we provethat the natural extension of the Volume Conjecture holds truefor an infinite family of hyperbolic links.     

Fast reversible isomerization of merocyanine as a tool to quantify stress history in elastomers

A mechanochemistry based approach is proposed to detect and map stress history during dynamic processes. Spiropyran (SP), a force sensitive molecular probe, was incorporated as a crosslinker into multiple network elastomers (MNE). When these mechanochromic MNEs are loaded, SP undergoes a well-known force-activated reaction to merocyanine (MC) changing its absorption in the visible range (visible blue color). This SP to MC transition is not reversible within the time frame of the experiment and the color change reports the concentration of activated molecules. During subsequent loading–unloading cycles the MC undergoes a fast and reversible isomerization resulting in a slight shift of absorption spectrum and results in a second color change (blue to purple color corresponding to the loading–unloading cycles). Quantification of the color changes by using chromaticity shows that the exact color observed upon unloading is characteristic not only of the current stress (reported by the shift in color due to MC isomerization), but of the maximum stress that the material has seen during the loading cycle (reported by the shift in color due to the change in MC concentration). We show that these two color changes can be separated unambiguously and we use them to map the stress history in the loading and unloading process occurring as a crack opens up and propagates, breaking the material. Color maps on fractured samples are compared with finite element simulations and the agreement is excellent.

A mechanochemistry based approach is proposed to detect and map stress history during dynamic processes.     

Conformational analysis and UV/Vis spectroscopic properties of a rotaxane-based molecular machine in acetonitrile dilute solution: when simulations meet experiments

A reduced form of a synthetic hydrogen-assembled molecular shuttle for nano-technological applications has been investigated by molecular dynamics simulations and density functional theory calculations. It is composed by a benzylic amide macrocycle mechanically locked onto a thread in acetonitrile solution. Classical sampling indicates, in agreement with experimental findings, that in equilibrium condition at 298 K the macrocycle and the naphthalimide radical anion moiety within the thread strongly interact forming four strong OCN-H-O=CNR hydrogen bonds. Simulations also revealed that the geometry of the supramolecular assembly reversibly oscillates between unfolded and folded conformations, with the latter characterized by an electrostatic hook involving the succinamide end group and the macrocycle itself. Finally, the simulated UV-Vis absorption spectra for free and complexed reduced naphthalimide quantitatively confirm that the transient spectroscopic change experimentally used as a probe for monitoring the translational motion of the macrocycle, from succinamide to naphthalimide stations, accompanying the selective electrochemical reduction.     

Carotenoids and lung cancer: biochemical aspects

Carotenoids are part of the human diet and a regular low-dose intake of these compounds from natural sources is normally preferred. Carotenoid supplementation in various diseases, including cancer, was described to be useful, but evidence has been obtained that high-dose supplementation of β-carotene may be unsafe, especially to smokers and asbestos-exposed workers, because of a stastically detected increased cancer risk. The negative effect might be mediated by carotenoid breakdown products having a high reactivity towards biomolecules. It has been suggested that these compounds originate from nonenzymatic cleavage of carotenoids by oxidants liberated in large amounts by neutrophils that accumulate in various inflammatory diseases and, in particular, in pulmonary disorders characterized by profound abnormalities in inflammatory pathways, such as those triggered by tobacco smoking. Carotenoid breakdown products, in turn, may affect neutrophil response in different ways that depend on the concentration that is reached by these products in the medium. In vitro studies show that nanomolar and micromolar concentrations of carotenoid derivatives stimulate superoxide production by neutrophils activated by phorbol myristate acetate (PMA), while a slight inhibition is noticed with cells activated by the chemotactic tripeptide N-formyl-Met-Leu-Phe (f-MLP). At higher concentrations, carotenoid breakdown products inhibit superoxide production in the presence of both PMA and f-MLP.      

New hybrid zirconium aminophosphonates containing piperidine and bipiperidine groups

The reaction of N-(phosphonomethyl)piperidine and N,N'-bis(phosphonomethyl)bipiperidine with zirconium(IV) in hydrofluoric acid media led to the preparation of two new zirconium fluoride phosphonate derivatives with 1D and 2D structure, respectively. Their structures were solved ab initio from laboratory powder X-ray diffraction (PXRD) data. The monophosphonate derivative, with formula ZrF(2)(HF)(O(3)PCH(2)NC(5)H(10)), has a 1D structure (triclinic, space group P ?1, a = 6.6484(3) ?, b = 7.1396(3) ?, c = 12.2320(6) ?, α = 77.932(4)°, β = 87.031(6)°, γ = 78.953(5)°, V = 557.22(4) ?(3), and Z = 2) made of inorganic chains constituted from the connection of zirconium octahedra and phosphorus tetrahedra with the piperidine groups bonded on their external part. The diphosphonate derivative, with formula Zr(2)F(4)(HF)(2)(O(3)PCH(2))NC(10)H(18)N(CH(2)PO(3)), has a 2D structure (triclinic, space group P ?1, a = 6.6243(3) ?, b = 7.2472(4) ?, c = 12.2550(7) ?, α = 102.879(4)°, β = 100.29(1)°, γ = 101.287(7)°, V = 547.03(4) ?(3), and Z = 1) composed of the packing of covalent layers whose structure may be ideally obtained by the joining of adjacent chains of the 1D compound. In these hybrid layers, inorganic regions made of the connectivity of zirconium octahedra and phosphorus tetrahedra alternate with organic regions represented by the bipiperidine moieties. A section dedicated to vibrational spectroscopy analysis is also included, mainly devoted to clarify some issues not easily deducible on the basis of PXRD data and to describe the fluorine environment inside zirconium phosphonate structures.     

Soft Nanostructured Films with an Ultra‐Low Volume Fraction of Percolating Hard Phase

In this study, aqueous emulsion polymerization of n‐butyl acrylate is performed in batch conditions without surfactants using a poly(acrylic acid)‐trithiocarbonate macro‐RAFT agent to control the polymerization and to stabilize the emulsion. According to the polymerization‐induced self‐assembly (PISA) approach, well‐defined amphiphilic PAA‐b‐PBA diblock copolymers form and self‐assemble during synthesis to yield highly stable core–shell particles with an extremely thin hard PAA shell. For the first time, we report here the specific properties of films obtained from these particular latexes. After drying the aqueous dispersion, tough and transparent films are obtained. Although the films are not chemically cross‐linked, they do not dissolve in good solvents for PBA. Moreover, they remain transparent even after immersion in water. Rheology shows that the films are both stiff and ductile, thanks to the nanostructured but very low volume fraction (less than 3 wt%) of PAA forming a percolating network in the soft PBA. Compared with conventional core–shell‐based films, this approach affords for the first time a route to a thin percolating honeycomb nanostructure with a sharp and strong interface between the two phases. The versatility of the synthetic procedure opens perspectives for a large range of functional materials.

     

Molecular Structure and Dynamics in Organic Solids: High Resolution Low Temperature 13 C NMR Studies

The development of cross polarization-magic angle spinning (CPMAS) has resulted in the achievement of near-liquid resolution in solid state ¹³ C NMR spectra. Therefore, the structure and dynamics of organic solids can now be studied on a carbon-by-carbon basis. Low temperature CPMAS capability permits the investigation of molecular dynamics in solids, and in particular in a temperature range heretofore inaccessible to high resolution NMR (15-200 K). We have developed and used low temperature CPMAS to study solid state effects on chemical exchange processes in organic and organometallic compounds and in carbonium ions. We have also developed a technique for measuring carbon-carbon bond lengths in amorphous solids using NMR. The geometry of cis-and trans-polyacetylene has been determined using this method.     

Temperature and aging dependence of strain‐induced crystallization and cavitation in highly crosslinked and filled natural rubber

We have investigated the structural changes occurring in highly crosslinked and carbon‐black filled natural rubber under uniaxial extension by small‐ and wide‐angle X‐ray scattering using synchrotron radiation. The experiments focused on strain‐induced crystallization (SIC) and nanocavitation and were carried out on a model series of materials as a function of temperature and aging conditions. We find that for all materials both SIC and cavitation decrease markedly with temperature and aging. However, the presence of carbon black filler shifts the ceiling temperature where SIC is observed to at least 120°C, presumably by a nucleating effect, maintaining the high strength of the elastomers. Interestingly, although in pure elastomers, the cavitation strength decreases with temperature, we find that in these filled elastomers the critical stress for the onset of cavitation increases significantly with temperature strongly suggesting that cavitation is due to the local confinement between fillers and supporting the idea of a glassy layer near the filler. Aging for 10 days at 110°C in oxygen‐free conditions decreases both SIC and cavitation and reduces the strength of the elastomer at high temperature. This is attributed to the formation of sulfur side chains hindering the crystallization. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 780–793     

Flow and Transport in Fractured Aquifers: New Conceptual Models Based on Field Measurements

We derived new equations of fracture aperture (or tube diameter) as functions of a tortuosity factor that can be used in discrete models and even in continuum equivalent models to simulate fluid flow and pollutant transport in fractured aquifers. MODFLOW/MT3DMS water velocity predictions have been compared with those obtained using a specific software application which solves flow and transport problems in a 3D set of parallel fissures. The results of a pumping/tracer test carried out in a fractured limestone aquifer in Bari (Southern Italy) have been used to calibrate advective/dispersive tracer fluxes given by the applied models. The mean tracer velocity given by a breakthrough curve was greater than values predicted by continuum models. This discrepancy increased when the hydraulic conductivity of the considered fractured medium decreased. Successful simulations of flow and transport in the fractured limestone aquifer are then achieved by accommodating a new tortuosity factor in models. The importance of the proposed tortuosity factor correction lies in the possibility of taking into account the effective tracer velocity during flow and transport simulations in fractures even when using a continuum model.     

Brownian Particle in a Poisson-Shot-Noise Active Bath: Exact Statistics,Effective Temperature,and Inference

The dynamics of an overdamped Brownian particle in a thermal bath that contains a dilute solution of active particles is studied. The particle moves in a harmonic potential and experiences Poisson shot-noise kicks with specified amplitude distribution due to moving active particles in the bath. From the Fokker–Planck equation for the particle dynamics, the stationary solution for the displacement distribution is derived along with the moments characterizing mean, variance, skewness, and kurtosis, as well as finite-time first and second moments. An effective temperature is also computed through the fluctuation–dissipation theorem and show that equipartition theorem holds for all zero-mean kick distributions, including those leading to non-Gaussian stationary statistics. For the case of Gaussian-distributed active kicks, a re-entrant behavior from non-Gaussian to Gaussian stationary states and a heavy-tailed leptokurtic distribution across a wide range of parameters are found as seen in recent experimental studies. Further analysis reveals statistical signatures of the irreversible dynamics of the particle displacement in terms of the time asymmetry of cross-correlation functions. Fruits of the work is the development of an compact inference scheme that may allow experimentalists to extract the rate and moments of underlying shot-noise solely from the statistics the particle position.