Does Electrical Conductivity of Linear Polyelectrolytes in Aqueous Solutions Follow the Dynamic Scaling Laws? A Critical Review and a Summary of the Key Relations

In this review, we focus on the electrical conductivity of aqueous polyelectrolyte solutions in the light of the dynamic scaling laws, recently proposed by Dobrynin and Rubinstein, to take into account the polymer conformations in different concentration regimes, both in good and poor solvent conditions. This approach allows us to separate contributions due to polymer conformation from those due to the ionic character of the chain, and offers the possibility to extend the validity of the Manning conductivity model to dilute and semidilute regimes. The electrical conductivity in the light of the scaling approach compares reasonably well with the observed values for different polyelectrolytes in aqueous solutions, over an extended concentration range, from the dilute to the semidilute regime

How toxic are gold nanoparticles? The state-of-the-art.

With the growing interest in biotechnological applications of gold nanoparticles and their effects exerted on the body, the possible toxicity is becoming an increasingly important issue. Numerous investigations carried out, in the last few years, under different experimental conditions, following different protocols, have produced in part conflicting results which have leaded to different views about the effective gold nanoparticle safety in human applications. This work is intended to provide an overview on the most recent experimental results in order to summarize the current state-of-the-art. However, rather than to present a comprehensive review of the available literature in this field, that, among other things, is really huge, we have selected some representative examples of both in vivo and in vitro investigations, with the aim of offering a scenario from which clearly emerges the need of an urgent and impelling standardization of the experimental protocols. To date, despite the great potential, the safety of gold nanoparticles is highly controversial and important concerns have been raised with the need to be properly addressed. Factors such as shape, size, surface charge, surface coating and surface functionalization are expected to influence interactions with biological systems at different extents, with different outcomes, as far as gold nanoparticle potentiality in biomedical applications is concerned. Moreover, despite the continuous attempt to establish a correlation between structure and interactions with biological systems, we are still far from assessing the toxicological profile of gold nanoparticles in an unquestionable manner. This review is intended to provide a contribution in this direction, offering some suggestions in order to reach the systematization of data over the most relevant physico-chemical parameters, which govern and control toxicity, at different cellular and organismal levels

Stepwise dehydration of Cd-exchanged levyne:thermal stability and structural modifications

Zeolites show remarkable properties that can be tuned through cation exchange of their original extraframework content. In this respect, the response of the modified zeolite to the heating stimuli, in terms of structural modifications and thermal stability, can drastically change and is therefore an important factor to consider. In this study, the dehydration mechanism of a natural levyne previously exchanged with Cd2+ has been monitored in situ by single crystal X-ray diffraction. The initial dehydration trend between 50 and 175°C is similar to that observed for the pristine material, levyne-Ca. The water loss is accompanied by extraframework cation migration within the zeolitic cavities and the unit-cell volume slightly contracts from 3503.8(1) to 3467.8(6) Å3. From 200 to 250°C, a pronounced drop of the unit-cell volume (-7%) is observed. The dehydrated structure at 250°C corresponds to levyne B topology of natural levyne, characterized by the statistical rupture of the T-O-T bonds of the double six-ring membered cage. However, in contrast to levyne-Ca, the fraction of broken connections reached 50% instead of 37%, and no additional structural modifications were detected up to 350°C. At 400°C, diffraction data pointed to the onset of the structural collapse. At this temperature, the measured unit-cell volume was 8% smaller compared to that of the RT structure. The corresponding contracted structure did not rehydrate after exposure to humid conditions for 21 days

Effective Equations of Motion for Quantum Systems

In many situations, one can approximate the behavior of a quantum system, i.e. a wave function subject to a partial differential equation, by effective classical equations which are ordinary differential equations. A general method and geometrical picture is developed and shown to agree with effective action results, commonly derived through path integration, for perturbations around a harmonic oscillator ground state. The same methods are used to describe dynamical coherent states, which in turn provide means to compute quantum corrections to the symplectic structure of an effective system.Comment: 31 pages; v2: a new example, new reference

Effective Constraints and Physical Coherent States in Quantum Cosmology: A Numerical Comparison

A cosmological model with a cyclic interpretation is introduced, which is subject to quantum back-reaction and yet can be treated rather completely by physical coherent state as well as effective constraint techniques. By this comparison, the role of quantum back-reaction in quantum cosmology is unambiguously demonstrated. Also the complementary nature of strengths and weaknesses of the two procedures is illustrated. Finally, effective constraint techniques are applied to a more realistic model filled with radiation, where physical coherent states are not available.Comment: 32 pages, 25 figure

2D Coordination Polymers Based on Isoquinoline-5-Carboxylate and Cu(II)

By combining isoquinoline-5-carboxilic acid with Cu(II) ions under several different conditions, we were able to obtain novel metallorganic materials, among which two 2D coordination polymers, CP 1 and CP 2 which were also characterized by SC-XRD. Ratio of solvents (EtOH : DMF) in the mixture employed during their synthesis has a marked effect in selecting the formation of one species or the other, which basically differ in the coordination at the Cu(II) center due to k1/k2 denticity of the carboxylate ligands.Two 2D coordination polymers which exclusively form depending on DMF : EtOH solvent mixture, fully characterized by SC-XRD, are among the novel materials formed by the combination of Cu(II) with isoquinoline-5-carboxylate ligand described here.imag

Role of lone-pair electron localization in temperature-induced phase transitions in mimetite.

The crystal structure of mimetite Pb5(AsO4)3Cl, a phosphate with apatite structure-type has been investigated in situ at 123, 173, 273, 288, 353 and 393 K. A careful inspection of the diffraction pattern and subsequent structure refinements indicated that mimetite transforms from the monoclinic to the hexagonal polymorph with increasing temperature. At 123 K, a monoclinic superstructure, mimetite-2M, with cell parameters a = 20.4487 (9),  b = 7.4362 (2), c = 20.4513 (9) Å, β = 119.953 (6)°, V = 2694.5 (2) Å3 and space group P21 was observed. From 173 to 353 K, the reflections of the supercell were evident only along one direction of the corresponding hexagonal apatite-cell and the structure transforms to the polymorph mimetite-M with space group P21/b and unit-cell parameters a = 10.2378 (3), b = 20.4573 (7), c = 7.4457 (2) Å, β = 120.039 (5)°, V = 1349.96 (9) Å3. Only at higher temperature, i.e. 393 K, does mimetite adopt the hexagonal space group P63/m characteristic of apatite structure-types. The role of the electron lone pairs of Pb atoms in the phase transition was investigated through the analysis of the electron localization function (ELF) calculated based on the DFT-geometry optimized structures of the three polymorphs. The changes in spatial distribution of the 6s2 electron density during the phase transitions were explored by means of the Wannier Function Centres (WFCs) derived from ab initio molecular dynamics trajectories. In the high-temperature hexagonal structure the 6s2 electrons are spherically symmetric relative to the position of Pb atoms. At low temperature the maximum of 6s2 electron density is displaced relative to the position of Pb atom contributing to the polar interaction in the monoclinic polymorphs

Poly[(μ-2-hy­droxy-3,5-dinitro­benzoato)rubidium]

The asymmetric unit of the title compound, [Rb(C7H3N2O7)]n, comprises an Rb+ cation and a 3,5-dinitro­salicylate ligand. The Rb+ cation is 10-coordinated by O atoms from eight 3,5-dinitro­salicylate anions and is linked by three μ2-O atoms, forming a zigzag chain along the b-axis direction, which is further linked by the phenyl groups, giving the three-dimensional framework. The crystal structure involves intra-anionic O—H⋯O hydrogen bonds and strong π–π stacking inter­actions [centroid-centroid distance = 3.6755 (7) Å]