The synthesis and the gas sensing properties of novel mixed phase (i.e., tetragonal and orthorhombic phase) coexistence SnO 2 nanorods are presented. The mixed phases SnO 2 nanorods were obtained by calcinations of SnC 2 O 4 synthesized with a chemical precipitation method using SnCl 2 •2H 2 O and PEG 400 as precursors. The resulting nanorods appear as polycrystalline composed of spherical mixed phases SnO 2 nanocrystals and have a high surface area. It was observed that the calcination temperature was the key parameter determining the content of the orthorhombic phase. The as-synthesized compounds were used as sensing materials of the sensors of indirect heating structure and tested for their ability to detect volatile organic compounds (VOCs), such as isopropanol, acetone, alcohol, and formaldehyde. Gas sensing tests showed that these mixed phases SnO 2 nanorods are highly promising for gas sensor applications, as the gas response for isopropanol was significantly enhanced by the presence of orthorhombic phase (S = 61.5 at 1000 ppm isopropanol and response time and recovery time of 4 and 10 s). The as-prepared two phases SnO 2 nanorods with the highest content of the orthorhombic phase exhibit excellent gas response, selectivity, and stability toward isopropanol gas at the optimized operating temperature of 255 °C. The enhancement in sensitivity is attributed to the presence of small orthorhombic SnO 2 crystals with average radius shorther than the Debye screening length of 7 nm for SnO 2 .

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A combined strategy utilizing experimental (infrared, nuclear magnetic resonance, circular dichroism, X-ray) and computational (time-dependent density functional theory) techniques is illustrated on tripeptides to investigate their chiroptical properties. Eight stereoisomers of monosubstituted ferrocene, Boc-Pro-Pro-Ala-NHFc, have been prepared and conformationally characterized in depth to reach some guidelines for a future design of ferrocene-based chromophores. The origin of the sign change in circular dichroism spectra near the absorption maximum of a ferrocene chromophore (about 470 nm) is strongly correlated with the sign of the dihedral angle describing deviation of the directly attached amide plane from planarity of the cyclopentadienyl ring. These findings may provide some guidelines for the design of new chiroptical ferrocene-based probes for the assignment of the screw-sense preference of short peptides.

Abstract:The synthesis and conformational analysis of a series of the monosubstituted aminoferrocene-based peptides bearing homo-and heterochiral Pro-Ala sequences are described. A change of the Pro amino acid chirality can affect the secondary structure. The homochiral derivatives of tBuCO-AA 2 -AA 1 -NHFc (Fc = ferrocene; AA = Pro, Ala) favour -turns, and a disruption of the secondary structure is observed for the heterochiral analogues in solution. A detailed computational study suggested that γ-turns form in the heterochiral derivatives. The X-ray-de-

Highly crystalline SrFe 2/3 Te 1/3 O 3 , Ba 3 Fe 2 TeO 9 , and Ba 2 NiTeO 6 have been synthesized by using a specially developed sol−gel route methodology, reducing the time needed employing solid-state routes and resulting in high reaction yield up to 75%. These materials have been studied by X-ray powder diffraction (XRPD), scanning and transmission electron microscopy, Raman spectroscopy, and dielectric and magnetic measurements. At room temperature, the crystal structure of SrFe 2/3 Te 1/3 O 3 is cubic, space group Pm3̅ m, with a = 3.9373(2) Å, whereas Ba 3 Fe 2 TeO 9 crystallizes in the hexagonal crystal system, space group P6 3 /mmc, a = 5.7691(4) Å, and c = 14.208(1) Å. The third studied perovskite Ba 2 NiTeO 6 crystallizes in the trigonal R3̅ m space group with a = 5.7974(4) Å and c = 28.599(2) Å. Based on structural characterization results, the obtained single and double perovskite crystallites are nearly in nanometer regime, ranging from 45 to 164 nm, building micrometer-sized particles with visible well-faceted hexagonal morphology. Magnetic measurements show the onset of ferrimagnetic ordering at relatively high temperature of 667 K for the SrFe 2/3 Te 1/3 O 3 , whereas Ba 3 Fe 2 TeO 9 and Ba 2 NiTeO 6 show antiferromagnetic ordering below 80 and 8.6 K, respectively. The measured room temperature dielectric constants are in the range between 15 and 77.