Volume 230, Issue 9 - Special Issue: The First European Conference on Physical and Theoretical Chemistry, Catania / Guest Editors: Salvatore Coluccia and Eckart Rühl

In this work the analysis by Laser Induced Breakdown Spectroscopy (LIBS) technique of copper-based alloys having different composition and performed with fs laser pulses is presented. A Nd:Glass laser (Twinkle Light Conversion, λ  = 527 nm at 250 fs) and a set of bronze and brass certified standards were used. The inverse Calibration-Free method (inverse CF-LIBS) was applied for estimating the temperature of the fs laser induced plasma in order to achieve quantitative elemental analysis of such materials. This approach strengthens the hypothesis that, through the assessment of the plasma temperature occurring in fs-LIBS, straightforward and reliable analytical data can be provided. With this aim the capability of the here adopted inverse CF-LIBS method, which is based on the fulfilment of the Local Thermodynamic Equilibrium (LTE) condition, for an indirect determination of the species excitation temperature, is shown. It is reported that the estimated temperatures occurring during the process provide a good figure of merit between the certified and the experimentally determined composition of the bronze and brass materials, here employed, although further correction procedure, like the use of calibration curves, can be demanded. The reported results demonstrate that the inverse CF-LIBS method can be applied when fs laser pulses are used even though the plasma properties could be affected by the matrix effects restricting its full employment to unknown samples provided that a certified standard having similar composition is available.

Ce:YAG-poly(methyl methacrylate) (PMMA) composites were prepared by using a melt compounding method, adding several amounts of Ce:YAG in the range 0.1–5 wt. %. The optical properties of the obtained composites and of the composites combined with a blue LED were measured to investigate the effect of the amount of Ce:YAG on the resulting emitted light in view of possible application in white LED manufacture. An increase in Ce:YAG amount caused an increase in the emission and a shift of 15 nm, influencing the white LED performance. The structure and morphology of the composites were studied. The results show that the interaction between the two components, observed by using solid state NMR experiments, are the responsible for the observed shift.

Preferential growth of anatase crystallites along different directions is known to deeply affect their photocatalytic properties, especially with respect to the exposure of the reactive {001} facets. Its extent can be easily quantified through simple geometric calculations, on the basis of crystal sizes extracted for specific directions by means of X-Ray Diffraction data analysis. Nevertheless, the actual results depend on the method employed for such a quantification. Here we report on a comparative morphological investigation, performed by employing the Scherrer equation and the line profile from Rietveld refinements, on shape-controlled anatase photocatalysts produced by employing HF as capping agent. Compared to the Rietveld-based method, the use of the Scherrer equation produces a systematic underestimation of crystallite dimensions, especially concerning the [100] direction, which in turn causes the percentage of exposed {001} crystal facets to be underestimated. Neglecting instrumental-related effects may further reduce the estimate.

Elastic small-angle X-ray scattering (SAXS) of free silica (SiO 2 ) nanoparticles is reported ( d  = 100–180 nm). The particles were prepared by a modified Stöber synthesis in narrow size distributions with controlled surface roughness and functionalization. Angle-resolved small-angle X-ray scattering patterns are shown to be sensitive to these changes in particle properties. It is reported that there is an exponential decrease in scattered X-ray intensity towards larger scattering angles as well as distinct oscillations, which is fully explained by Mie theory. Small-angle X-ray scattering of mesoporous nanoparticles with rough surfaces is compared to that of microporous nanoparticles with smooth surfaces, revealing distinct differences that are rationalized by diffuse scattering from nanoparticle pores in addition to the dominating contribution of Mie scattering. Furthermore, results from small-angle X-ray scattering experiments on functionalized silica nanoparticles are presented, where the incorporation of the dye fluorescein isothiocyanate is found to cause changes in the optical properties of the nanoparticles, as compared to non-functionalized samples. Small, but distinct deviations in particle size derived from electron microscopy and from small-angle X-ray scattering are observed. These are rationalized by particle shrinking occurring in electron microscopy as well as slight changes in optical properties of the nanoparticle samples.

The use of titanium dioxide as heterogeneous photocatalyst is drawing considerable attention for water and air purification and remediation. Recently, TiO 2 particles have been modified in order to make this material attractive for industrial and environmental remediation usage. In the present study, phenolic compounds of olive mill wastewater (OMW) were degraded in the presence of glucose-doped titanium particles (CDT) through a photocatalysis process activated by visible light. The photocatalyst effectiveness towards the polluted wastewater from olive oil industry was tested on systems having different initial concentrations of phenols and in the presence of different amounts of CDT. For kinetic analysis the role of Ti/TPh ratio (amount of catalyst/amount of total phenols) was investigated. The rate constant ( k 2 ) and the amounts of species adsorbed on adsorbent at equilibrium ( q e ) of each reaction were calculated by fitting kinetics data to a second-order kinetic adsorption model. The results collected at different Ti/TPh ratios showed that the amount of phenols that can be removed from the water solution linearly increases with the Ti/TPh ratio till a maximum value (optimal ratio) at which no further degradation of phenolic compounds was obtainable. Such kind of parameter allows to identify the optimal value of catalyst and the initial substrate concentration for a high level of degradation. The results showed in this study can have an important impact for an applicative point of view.

In this review, results of recent studies on the electrochemical stability and degradation properties of poly(3,4-ethylenedioxythiophene) films are summarized, with particular emphasis on the structural changes induced by overoxidation and electrochemical degradation. The most important electrodeposition methods for the preparation of PEDOT films in surfactant free aqueous media have also been summarized, and several experimental techniques suitable for monitoring the degradation process have been discussed. Morphological changes in PEDOT films during overoxidation have been analyzed. Overoxidation mechanisms proposed in the literature have been surveyed.

We show the temporal change in repassivation mechanism as a time-dependent linear combination of a high-field model of oxide growth (HFM) and the point defect model (PDM). The observed switch in transient repassivation current-decrease under potentiostatic control occurs independently of the active electrode size and effective repassivation time for all applied overpotentials. For that, in situ depassivation of plasma electrolytically oxidized (PEO) coatings on aluminium was performed with nanosecond laser pulses at 266 nm and the repassivation current transients were recorded as a function of pulse number. A mathematical model combines the well established theories of oxide-film formation and growth kinetics, giving insight in the non linear transient behaviour of micro-defect passivation. According to our findings, the repassivation process can be described as a charge consumption via two concurrent channels. While the major current-decay at the very beginning of the fast healing oxide follows a point-defect type exponential damping, the HFM mechanism supersedes gradually, the longer the repassivation evolves. Furthermore, the material seems to reminisce former laser treatments via defects built-in during depassivation, leading to a higher charge contribution of the PDM mechanism at higher pulse numbers.

The intrinsic fluorescence of recombinant proteins offers a powerful tool to detect and characterize structural changes induced by chemical or biological stimuli. We show that metal-ion binding to a hexahistidine tail can significantly broaden the range of such structurally sensitive fluorescence observables. Bipositive metal-ions as Cu 2+ , Ni 2+ and Zn 2+ bind 6xHis-tag azurin and its 6xHis-tagged R129W and W48A-R129W mutants with good efficiency and, thereby, quench their intrinsic fluorescence. Due to a much more favourable spectral overlap, the 6xHis-tag/Cu 2+ complex(es) are the most efficient quenchers of both W48 and W129 emissions. Based on simple Förster-type dependence of energy-transfer efficiency on donor/acceptor distance, we can trace several excitation-energy transfer paths across the protein structure. Unexpected lifetime components in the azurin 6xHis-tag/Cu 2+ complex emission decays reveal underneath complexity in the conformational landscape of these systems. The new tryptophan emission quenching paths provide additional signals for detecting and identifying protein structural changes.

Multidentate binding of two helical hexapeptides to a gold surface was obtained by introducing in the peptide chain a non ribosomial amino acid, i.e. the 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) residue, a C α -tetrasubstituted α -amino acid bearing a heterocyclic side chain characterized by a disulfide group. The two peptides, mainly formed by strongly helicogenic C α -tetrasubstituted α -amino acids, were both functionalized at the N-terminus by a ferrocenoyl (Fc) group, but differ in the number of Adt residues included in the peptide chain: the former (Fc6Adt2) contains two Adt residues at positions 1 and 4, while its analog (Fc6Adt1) contains a single Adt at position 4, since the Adt at position 1 is substituted by an α -amino isobutyric acid (Aib) residue. This peptide design allowed us to explore the different electrochemical properties and morphologies shown by the two peptide layers immobilized on a gold surface by two (Fc6Adt2) or a single (Fc6Adt1) bidentate linker, respectively. The electrochemical activity of the ferrocenoyl probe embedded in the peptide film was characterized by cyclic voltammetry, chronoamperometry and square wave voltammetry, while the binding and the morphology of the peptide layers were studied by X-ray photoelectron spectroscopy (XPS) and ultra high vacuum scanning tunneling microscopy (UHV-STM), respectively. Significant differences were observed in the electron transfer (ET) properties of the two peptides investigated, which emerge from the diverging morphology achieved by the peptide layers on the gold surface. It was found that while a standing-up configuration of the peptide layer, realized by a single bidentate linkage, maximizes the ET efficiency, a lying down configuration (two Adt linkages) allows for precise positioning of Fc in the proximity of a gold surface.

The M06-2X, TPSS, and B3PW91 density functionals and the classical ab initio MP2 method were used to study microsolvation around the protonated trialanine, Ala 3 H + . All adopted electronic structure approaches show the formation of wires or compact ring clusters of water molecules strongly bonded to peptidic polar groups through hydrogen bonds with hydration energy ranging from − 93 to –66 kcal mol – 1 . Independently from the adopted electronic structure methods, explicit water molecules favor peptidic chain with the polyproline II (PPII) conformation, thus the electronic energy stability order of the four unfolded conformers follows the sequence: PPII-PPII >  β -PPII ∼ PPII- β  >  β - β , while entropy favors the reversed order. The delicate balance of electronic energy (or enthalpy) and entropy modulated by the temperature accounts for the change in abundance of the PPII and β conformations experimentally observed. The proposed bottom-up approach has been developed following the energetically dominant polar groups of peptide and water dipoles interactions. The intrapeptide dipole decoupling, caused by the β  → PPII transformation, and the consequent greater dipole coupling with water molecules provide a rational base to explain the energy gain due to the explicit water coordination to PPII residues.

Scleroglucan (Sclg) is a polysaccharide that exhibits a triple helix conformation (triplex), both in aqueous solution and in the solid state, which is lost in DMSO solution, at high temperature and at high pH values. The triplex conformation is characterized by a high rigidity, responsible of Sclg peculiar properties. Although the relative stability of triplex and single strand has already been investigated, different structural details are still missing. In the present study, we analyse the structural properties and the factors stabilizing the single chain and the triple helix of Sclg in different conditions. To this end, we simulated both systems in water and in DMSO. The triple helix has been also simulated in the presence of chemical damages on one of the three strands (to reproduce in silico the effect of sonication) or by inducing a partial unfolding of the triplex structure. The computational results have been compared with experimental evidences in which the triplex denaturation, at alkaline pH values, has been followed by monitoring the UV and CD spectra of Congo red, used as a probe molecule. Our results indicate that sonication breaks the Sclg chains without appreciably changing the stability of the other tracts of triple helix. The simulated perturbed or partially unfolded triplexes show a clear tendency to form less ordered aggregates. Finally, our simulations put in evidence an important role of the hydrophobic interactions both in the triplex stability and in the aggregation processes observed after induced denaturation.

The atomic structure of calcium-silicate-hydrate (C 1.67 –S–H x ) has been studied. Atomistic C–S–H models suggested in our previous study have been revised in order to perform a direct comparison of energetic stability of the different structures. An extensive set of periodic structures of C–S–H with variation of water content was created, and then optimized using molecular dynamics with reactive force field ReaxFF and quantum chemical semiempirical method PM6. All models show organization of water molecules inside the structure of C–S–H. The new geometries of C–S–H, reported in this paper, show lower relative energy with respect to the geometries from the original definition of C–S–H models. Model that corresponds to calcium enriched tobermorite structure has the lowest relative energy and the density closest to the experimental values.

The performance of exchange-correlation functionals for the description of atomic excitations is investigated. A benchmark set of excited states is constructed and experimental data is compared to Time-Dependent Density Functional Theory (TDDFT) calculations. The benchmark results show that for the selected group of functionals good accuracy may be achieved and the quality of predictions provided is competitive to computationally more demanding coupled-cluster approaches. Apart from testing the standard TDDFT approaches, also the role of self-interaction error plaguing DFT calculations and the adiabatic approximation to the exchange-correlation kernels is given some insight.

A new transmission FTIR set-up has been developed to investigate photocatalytic reactions under in situ UV-Vis illumination and in controlled atmosphere. This system was employed to study the evolution of the surface species during the photodegradation of phenol and oxalic acid on TiO 2 P25. As far as phenol is concerned, dosage from the gas phase on the activated oxide surface resulted in dissociative adsorption for coverages below the monolayer and in physisorption beyond this limit. Experiments under UV irradiation showed no relevant photocatalytic activity in absence of O 2 , the only spectroscopic consequence being the increase of a monotonic IR absorption, covering nearly the whole MIR range, related to UV-generated free conduction electrons. Only the contemporary addition of O 2 and H 2 O to the TiO 2 /phenol system allowed us to observe an efficient photodegradation reaction and to highlight the IR manifestations of some of the photodegradation products which are formed. In particular, oxalic acid appeared to be the main intermediate product adsorbed at the oxide surface during phenol photodegradation. For this reason the photoreactivity of pure oxalic acid on TiO 2 under UV irradiation was also investigated.