Nanosized zinc and magnesium ferrites obtained from PVA–metal nitrates’ solutions

The paper presents a study regarding the possibility of obtaining zinc and magnesium ferrites starting from poly(vinyl alcohol)–metal nitrates solutions. By controlled heating of these solutions, a redox interaction takes place leading to the formation of some coordination compounds of the involved metal cations with the oxidation products of poly(vinyl alcohol) (PVA). FT-IR spectroscopy has evidenced the disappearance of the NO ₃ ^? anions at 140 °C due to the redox interaction with PVA. Thermal analysis evidenced the difference in the interaction of the individual metal nitrates and PVA and thus the particularity of the preparation of each ferrite. The thermal decomposition of the synthesized precursors was finished below 400 °C as resulting from both thermal analysis and FT-IR spectroscopy. The obtained ferrites powders consist of fine nanoparticle with diameters ranging from 10 to 30 nm for the powders annealed at 500 °C, as resulting from the SEM images. The specific surface area of the powders obtained at 500 °C was 32.2 m² g^?1 for ZnFe₂O₄ and 21.7 m² g^?1 for MgFe₂O₄, characteristic of nanoscaled powders. The increasing of the annealing temperature at 1,000 °C leads to sintering of both ferrites, more advanced in the case of zinc ferrite.     

Preparation of CuFe2O4/SiO2 nanocomposite starting from Cu(II)–Fe(III) carboxylates embedded in hybrid silica gels

Nanocomposites of the type 30 % CuFe₂O₄/70 % SiO₂ were synthesized using the modified sol–gel method starting from tetraethylorthosilicate, metal nitrates (Fe(NO₃)₃·9H₂O, Cu(NO₃)₂·3H₂O) and the diol: 1,3-propane diol. The obtained hybrid gel, which contains within the pores, the metal nitrates and diol, was thermally treated at 140 °C, when the redox reaction between metal nitrates and 1,3-propane diol takes place forming Cu(II)–Fe(III) carboxylate compounds of malonate type. The thermal decomposition of the carboxylates within the gels pores, at ~300 °C, leads to simple or mixed metal oxides, uniformly distributed within the amorphous silica matrix. The spinel system CuFe₂O₄/SiO₂ was obtained starting with 700 °C. The evolution of the spinel phase with the annealing temperature was investigated and resulted that at 1,000 °C, the matrix crystallizes into cristobalite and quartz. The formation of bulk CuFe₂O₄, starting from the same type of Cu(II)–Fe(III) carboxylate compounds was also investigated. A comparison between the thermal evolution of bulk CuFe₂O₄ and CuFe₂O₄/SiO₂ starting from Cu(II)–Fe(III) carboxylate compounds was made. The magnetic behavior of the ferrite nanocrystallites depending on the annealing temperature was also investigated.     

How do Pseudoenantiomers Structurally Differ in the Gas Phase? An IR/UV Spectroscopy Study of Jet‐Cooled Hydroquinine and Hydroquinidine

The gas‐phase structures of the cinchona alkaloids, hydroquinine and its pseudoenantiomer hydroquinidine, are studied in a supersonic expansion by means of laser‐induced fluorescence and IR/UV double‐resonance spectroscopy. Vibrational spectroscopy combined with density functional calculations show that the conformational properties of the two pseudoenantiomers are identical. In both cases, they exist in two isoenergetic forms, with similar IR spectra. Both conformers are similar to the most stable cis‐γ‐open form of quinine; they differ from each other by the position of the ethyl substituent attached to the quinuclidine ring. Further differences between the two conformers are observed in the laser‐induced fluorescence spectrum. The first electronic transition is characterized by time‐dependent density functional theory and RI‐cc2 calculations, and is of ππ* nature. The results described here emphasize the role of the ethyl substituent in the structural differences between pseudoenantiomers of cinchona alkaloids.     

Mapping the Distribution of Melanin Concentration in Different Fitzpatrick Skin Types Using Hyperspectral Imaging Technique

Measuring skin melanin concentration in order to assess skin phototype according to Fitzpatrick's classification is a constant research goal. In this study, a new approach for assessing skin melanin concentration based on hyperspectral imaging combined with an appropriate analytical model that exploits specific spectral bands to generate maps of melanin content distribution on different Fitzpatrick skin phototypes is presented. Hyperspectral images from the proximal inner side of the forearms of 51 young volunteers covering the first four classes of Fitzpatrick's phototypes were acquired using a hyperspectral imaging system. The images were analyzed using a modified Beer–Lambert law that segregates the contribution of melanin from the other constituents to the skin absorption spectrum. The performance of the model was evaluated using the coefficient of determination (r-squared). The results revealed that the approach proposed in this study generated accurate melanin concentration distribution maps that allowed a correct classification of skin phototype. In conclusion, the proposed approach for assessing skin melanin concentration proved to be very reliable for classifying skin phototypes, and, as it provides maps that are easily read, it has the advantage of a possible extension of its applications to other research concerning skin pigmentation.