Photoelectrochemical Behavior of Electrophoretically Deposited Hematite Thin Films Modified with Ti(IV).

Doping hematite with different elements is a common strategy to improve the electrocatalytic activity towards the water oxidation reaction, although the exact effect of these external agents is not yet clearly understood. Using a feasible electrophoretic procedure, we prepared modified hematite films by introducing in the deposition solution Ti(IV) butoxide. Photoelectrochemical performances of all the modified electrodes were superior to the unmodified one, with a 4-fold increase in the photocurrent at 0.65 V vs. SCE in 0.1 M NaOH (pH 13.3) for the 5% Ti-modified electrode, which was the best performing electrode. Subsequent functionalization with an iron-based catalyst led, at the same potential, to a photocurrent of ca. 1.5 mA·cm(-2), one of the highest achieved with materials based on solution processing in the absence of precious elements. AFM, XPS, TEM and XANES analyses revealed the formation of different Ti(IV) oxide phases on the hematite surface, that can reduce surface state recombination and enhance hole injection through local surface field effects, as confirmed by electrochemical impedance analysis.

Conformational Analysis and Electronic Interactions of Some 4'-Substituted-2-ethylthio-phenylacetates.

The conformational analysis of various 4'-substituted-2-ethylthio-phenylacetate compounds bearing the substituents NO2 (1), Cl (2), H (3), Me (4), and OMe (5) was performed using infrared (IR) spectroscopic analysis of the carbonyl stretching band (νCO) supported by B3LYP/6-31G(d,p), NBO, QTAIM, and SM5.42R calculations for compounds 1, 3, and 5. The IR spectra in n-hexane indicate the presence of three components, whose intensities decrease upon increasing frequency. In solvents with high permittivity, while the low intensity component at higher frequency disappears, the relative intensity of the component at the intermediate frequency changes with respect to the lower frequency component with differing trends for the various derivatives. It can be observed that the intensity does not vary for compounds 1 and 2, which bear an electron-withdrawing substituent at 4', while it increases in intensity for compounds 3-5. The computational results predict the presence of three gauche conformers, defined by the orientation of the C-S bond with respect to the carbonyl group, whose intensities and νCO frequencies are in agreement with the experimental results. In solvents with increasing permittivity, the SM5.42R solvation model results reproduce the experimental trend observed for the two components in the low frequency region, while it overestimates the amount of the higher frequency conformer. NBO analysis suggests that all the conformers are stabilized to the same extent in the gauche conformation via σC-S → π*CO and πCO → σ*C-S orbital interactions. The different stability can be attributed to the geometrical arrangement of the C(O)-CH2-S-CH2-CH3 moiety, which assumes a six-membered chair-like geometry in the g1 conformer, a six-membered twisted-chair-like geometry in the g2 conformer, and a seven-membered chair-like ring in the g3 conformer. Quantum theory of atoms in molecules (QTAIM) indicates that the ring geometries were formed and stabilized from short contacts between the oppositely charged carbonyl oxygen and the methylene/methyl hydrogen atoms, which interact through unusual intramolecular electrostatic hydrogen bonding that satisfies the Popelier criteria.

Conformational study of some 4'-substituted 2-(phenylselanyl)-2-(ethylsulfanyl)-acetophenones.

The conformational analysis of some 4'-substituted 2-(phenylselanyl)-2-(ethylsulfanyl)-acetophenones bearing the substituents NO2 (1), Br (2), H (3), Me (4) and OMe (5) was performed by ν(CO) IR analysis, B3LYP/6-31+G(d,p) and single point polarisable continuum model (PCM) calculations, along with NBO analysis for 1, 3 and 5. Calculations for 1-5 indicate the existence of three stable conformations, c1, c2 and c3, whose stability depends on the balance between electrostatic and orbital interactions that are strictly related to the geometrical arrangement. The comparison between the experimental IR spectra in solution and the computed data in gas phase for 1-5 allows the c1 conformer to be assigned to the less intense component at higher frequency of the carbonyl doublet and both the c2 and c3 ones to the more intense lower frequency component. The sum of the calculated molar fraction of c2 and c3 conformers decreases from 95% to 63% on going from 1 to 5 (in gas phase), and this trend compares well with the PCM calculations and the IR experimental data for the majority of the solvents for all compounds 1-5. The NBO analysis for 1, 3 and 5 shows that the sum of the relevant orbital delocalization energies for the c1, c2 and c3 conformers is almost constant and does not match the computed stability order. The lowest stability of the c1 conformer for 1-3 can be related to the small value of the α dihedral angle that enables a strong electrostatic destabilizing repulsion between the O(CO)(δ-)…S(δ-) atoms. The relative stability of the c1 conformer increases for 4 and 5 as the α dihedral angle enlarges and the repulsion is minimized. Moreover, the strong repulsive field effect between the C(δ+)=O(δ-) and C(δ+)-S(δ-) dipoles exerted to a greater extent on the c1 conformers of 1-3 with respect to 4 and 5, causes a major increase of the corresponding C=O bond orders and related carbonyl frequencies. For the c2 conformer, the electrostatic destabilizing repulsion between the O(δ-)…Se(δ-) atoms is weaker than that involving the O(δ-)…S(δ-) atoms in the c1 conformer and therefore has negligible effects on the conformer stability that is mainly determined by the sum of the orbital interactions. The c3 conformer has the shortest S(δ-)…Se(δ-) contact for all compounds and thus the related electrostatic repulsion seems to be the most important factor that affects its stability. In conclusion, the computed order of stability of the three conformers for 1-5 depends on the electrostatic repulsions between close charged atoms rather than on the sum of the orbital delocalization energies that are quite similar for all the conformers.

Symbolic or utilitarian? Juggling interpretations of Neanderthal behavior: new inferences from the study of engraved stone surfaces.

Different categories of finds reveal how Neanderthals have manifested at different moments behaviors not ascribable to the utilitarian sphere, but to the aesthetic or symbolic. When the majority of this evidence dates to the few millennia that preceded the spread of Anatomically Modern Humans in Europe, these are grounds to continue the debate regarding the emergence of complex behavior, seen as an autonomous phenomenon of Neanderthal man or as the result of contact with immigrant populations. Re-examination of pebbles or flaked stones, a large part of such evidence, using a rigorous technological and taphonomic approach integrated with experimental tests, has already revealed these materials to be insignificant or natural, rather than anthropic, in origin. The following work seeks to shed light on the uncertainty existing around those stones and lithic artefacts bearing surface lines and scratches; these are of doubtful anthropic origin, but have not, as yet, been definitively interpreted. Generally, these findings are occasional in Mousterian sites, and when they are recovered with an excellent degree of preservation, different methods and levels of observation can be used for investigating them. The case studies taken into account are three sites in north Italy, where the surfaces of pebbles and flakes reveal a variety of signs and modifications attributable to various utilitarian acts. Of these, preventive cleaning of flint nodules has not been excluded, even if the traces on some tools reveal intentionality and repetition of gestures applied to the construction of a curated artifact.

Conformational analysis of some N,N-diethyl-2-[(4'-substituted) phenylthio] acetamides.

The conformational analysis of some N,N-diethyl-2[(4'-substituted)phenylthio]acetamides bearing the substituents OMe 1, Me 2, H 3, Cl 4, Br 5 and NO26, was performed by νCO IR analysis, along with B3LYP/6-311++G(d,p) and Polarisable Continuum Model (PCM) calculations, as well as NBO analysis for 1, 3, and 6 and X-ray diffraction for 4. The results of the calculations indicated the existence of two stable conformation pairs, i.e. gauche (anti; syn) (most stable) and cis (anti; syn) in the gas phase. The gauche conformers were less polar with respect to the cis ones for 1 and 3, but more polar for 6. The most intense IR carbonyl doublet component observed at the lower frequency can be ascribed to the gauche conformers g(anti; syn) for 3-6 in n-C6H14, which is in agreement with the gauche and cis relative stabilities and frequencies resulting from the PCM calculations. Similarly, the single IR band for 1 and 2 in n-hexane may be attributed to the gauche conformers. The PCM calculations compared well with the IR data for the compounds in solution, showing that there is a progressive increase of the cis/gauche population ratio as the solvent polarity increases. The NBO analysis indicated that the gauche(anti; syn) conformation in the gas phase was stabilized by the relevant LPS4→πC2O1(∗),πC2O1→σC3S4(∗),σC3S4→πC2O1(∗),πC2O1(∗)→σC3S4(∗), and LPO1→σ(∗)C11H28 orbital interactions, which were absent in the cis(anti; syn) conformer. On the contrary, the cis conformer for derivatives 1, 3, and 6 were stabilized by the σC3-S4(∗)→σ(∗)C2N5 orbital interaction (through bond coupling), along with the additional LPO1→σ(∗)S4C10 interaction for 6. Moreover, the electrostatic repulsion between the C(δ+)S(δ-) and C(δ+)O(δ-) dipoles (Repulsive Field Effect) contributed to both the larger destabilization and increase of the νCO frequency of the cis conformer with respect to the gauche conformer. X-ray single crystal analysis indicates that compound 4 assumes the c2(anti) conformation in the solid state, which is the conformation obtained by compound 6 in the gas phase. To obtain the largest energy gain, the molecules were arranged in the crystal in a six-molecules synthon mediated by CH⋯O and Cl⋯Cl interactions, where the chlorine atoms were related by a crystallographic inversion center.