Color Bricks: Building Highly Organized and Strongly Absorbing Multicomponent Arrays of Terpyridyl Perylenes on Metal Oxide Surfaces

Terpyridine‐substituted perylenes containing cyclic anhydrides in the peri position were synthesized. The anhydride group served as an anchor for assembly of the terpyridyl‐crowned chromophores as monomolecular layers on metal oxide surfaces. Further coordination with Zn²⁺ ions allowed for layer‐by‐layer formation of supramolecular assemblies of perylene imides on the solid substrates. With properly selected anchor and linker molecules it was possible to build high quality structures of greater than ten successive layers by a simple and straightforward procedure. The prepared films were stable and had a broad spectral coverage and high absorbance. To demonstrate their potential use, the synthesized dyes were employed in solid‐state dye‐sensitized solar cells, and electron injection from the perylene antennas to titanium dioxide was observed.     

Dynamical invariants in the deterministic fixed-energy sandpile

The non-ergodic behavior of the deterministic Fixed Energy Sandpile (DFES), with Bak-Tang-Wiesenfeld (BTW) rule, is explained by the complete characterization of a class of dynamical invariants (or toppling invariants). The link between such constants of motion and the discrete Laplacians properties on graphs is algebraically and numerically clarified. In particular, it is possible to build up an explicit algorithm determining the complete set of independent toppling invariants. The partition of the configuration space into dynamically invariant sets, and the further refinement of such a partition into basins of attraction for orbits, are also studied. The total number of invariant sets equals the graphs complexity. In the case of two dimensional lattices, it is possible to estimate a very regular exponential growth of this number vs. the size. Looking at other features, the toppling invariants exhibit a highly irregular behavior. The usual constraint on the energy positiveness introduces a transition in the frozen phase. In correspondence to this transition, a dynamical crossover related to the halting times is observed. The analysis of the configuration space shows that the DFES has a different structure with respect to dissipative BTW and stochastic sandpiles models, supporting the conjecture that it lies in a distinct class of universality.     

Third-Order Phase Transition: Random Matrices and Screened Coulomb Gas with Hard Walls

Journal of Statistical Physics - Consider the free energy of a d-dimensional gas in canonical equilibrium under pairwise repulsive interaction and global confinement, in presence of a volume...     

Universal correlations and power-law tails in financial covariance matrices

We investigate whether quantities such as the global spectral density or individual eigenvalues of financial covariance matrices can be best modelled by standard random matrix theory or rather by its generalisations displaying power-law tails. In order to generate individual eigenvalue distributions a chopping procedure is devised, which produces a statistical ensemble of asset-price covariances from a single instance of financial data sets. Local results for the smallest eigenvalue and individual spacings are very stable upon reshuffling the time windows and assets. They are in good agreement with the universal Tracy-Widom distribution and Wigner surmise, respectively. This suggests a strong degree of robustness especially in the low-lying sector of the spectra, most relevant for portfolio selections. Conversely, the global spectral density of a single covariance matrix as well as the average over all unfolded nearest-neighbour spacing distributions deviate from standard Gaussian random matrix predictions. The data are in fair agreement with a recently introduced generalised random matrix model, with correlations showing a power-law decay.     

Aqueous Stable Gold Nanostar/ZIF‐8 Nanocomposites for Light‐Triggered Release of Active Cargo Inside Living Cells

A plasmonic core–shell gold nanostar/zeolitic‐imidazolate‐framework‐8 (ZIF‐8) nanocomposite was developed for the thermoplasmonic‐driven release of encapsulated active molecules inside living cells. The nanocomposites were loaded, as a proof of concept, with bisbenzimide molecules as functional cargo and wrapped with an amphiphilic polymer that prevents ZIF‐8 degradation and bisbenzimide leaking in aqueous media or inside living cells. The demonstrated molecule‐release mechanism relies on the use of near‐IR light coupled to the plasmonic absorption of the core gold nanostars, which creates local temperature gradients and thus, bisbenzimide thermodiffusion. Confocal microscopy and surface‐enhanced Raman spectroscopy (SERS) were used to demonstrate bisbenzimide loading/leaking and near‐IR‐triggered cargo release inside cells, thereby leading to DNA staining.     

A condition of indecomposability for Butler \mathrm B (n)-groups

We give a manageable sufficient condition for indecomposability of Butler \(\mathrm B (n)\) -groups, allowing the easy construction of a big family of indecomposable torsionfree Abelian groups of finite rank.     

Reflective Optics for Hard X-ray Nanofocusing Applications at the ESRF

The advent of high-brightness X-ray light sources has provided the impetus for the development of focusing systems capable of yielding spatially resolved information from samples at length scales below 10 nm. Beams of such dimensions are fundamental elements in a range of instruments providing powerful analytical tools for a broad range of scientific domains including life, materials, chemical, environmental, and physical sciences. At the ESRF, particular efforts have been made towards the design and implementation of reflective optical systems capable of routine nanoprobe formation at hard X-ray wavelengths (0.1 nm and below) with resolutions in the sub-50 nm range. Often, one of the principal driving forces for the use of such systems is the capacity of reflective optics to deliver very high photon fluxes to the sample. For imaging applications at the ESRF, monochromatic photon fluxes in excess of 10⁸ph/s/nm² are achievable at energies above 15keV—typically 1–2 orders of magnitude greater than accessible with current alternative technologies. Of course, such performance is not straightforward to achieve and requires considerable care both in the manufacture and implementation of the mirror systems. In this article, we describe some of the technological characteristics and limits of these optics and report on the performance of some of the systems currently in service at ESRF beamlines.     

Phosphodiester cleavage in ribonuclease H occurs via an associative two-metal-aided catalytic mechanism

Ribonuclease H (RNase H) belongs to the nucleotidyl-transferase (NT) superfamily and hydrolyzes the phosphodiester linkages that form the backbone of the RNA strand in RNA x DNA hybrids. This enzyme is implicated in replication initiation and DNA topology restoration and represents a very promising target for anti-HIV drug design. Structural information has been provided by high-resolution crystal structures of the complex RNase H/RNA x DNA from Bacillus halodurans (Bh), which reveals that two metal ions are required for formation of a catalytic active complex. Here, we use classical force field-based and quantum mechanics/molecular mechanics calculations for modeling the nucleotidyl transfer reaction in RNase H, clarifying the role of the metal ions and the nature of the nucleophile (water versus hydroxide ion). During the catalysis, the two metal ions act cooperatively, facilitating nucleophile formation and stabilizing both transition state and leaving group. Importantly, the two Mg(2+) metals also support the formation of a meta-stable phosphorane intermediate along the reaction, which resembles the phosphorane intermediate structure obtained only in the debated beta-phosphoglucomutase crystal (Lahiri, S. D.; et al. Science 2003, 299 (5615), 2067-2071). The nucleophile formation (i.e., water deprotonation) can be achieved in situ, after migration of one proton from the water to the scissile phosphate in the transition state. This proton transfer is actually mediated by solvation water molecules. Due to the highly conserved nature of the enzymatic bimetal motif, these results might also be relevant for structurally similar enzymes belonging to the NT superfamily.