Electrophysical properties of titanates of alkaline-earth metals

Results on oxygen-ion, electron, and proton conduction and oxygen penetrability of titanates of alkaline-earth metals doped with acceptor admixtures are briefly reviewed. The applicability of these materials in electrochemical devices, in particular, as oxygen-penetrable membranes, is considered. The focus is on the studies carried out at the Institute of High-Temperature Electrochemistry, Ural Branch, Russian Academy of Sciences.     

吡咯和呋喃气相质子化过程的密度泛函理论研究

Density functional theory and ab initio calculations have been used to determine structures and stabilities of the protonated aromatics species AH^＋ and AH2^2＋ （A=pyrrole, furan）. Possible mechanisms and relative energetics for protonation of pyrrole and furan by H3O^＋ and AH^＋ in the gas phase have been explored. Calculations show that the Cα-protonated species was the most stable structure for AH^＋, and the protonated AH^＋ might accommodate the second proton to yield AH2^2＋ if the free proton was available. The gas-phase H3O^＋ could protonate pyrrole and furan with significant exothermiCity and almost without barrier. The proton transfer from AH4^＋ to pyrrole and furan has a barrier ranging from 33.5 to 39.3 kJ/mol in the gas phase.     

Cationic Heteroconjugation Constants in the OHN+ and NHO+ Systems in Propylene Carbonate: Dependence on Difference in Basicity

Cationic heteroconjugation equilibria of more than ninety systems consisting of substituted pyridines, their N-oxides, and trimethylamine N-oxide, i. e., in systems with mixed hydrogen bridges of type OHN⁺ (NHO⁺) were studied in propylene carbonate. Both experimental systems without proton transfer, BH⁺/B₁, and those with proton transfer, B₁H⁺/B, were explored. The stability of the mixed hydrogen bridges, OHN⁺ (NHO⁺), is compared with that of the OHC⁺-type bridges. The influence of the difference in basicity of the conjugate base of the proton donor and the proton acceptor on the presence of the proton transfer equilibria, and, consequently, the possibility of determination of the cationic heteroconjugation constant values is discussed.     

A Novel Proton Sensor with Luminescence and Color Signaling Based on Platinum(II) Terpyridyl Acetylide Complex

Molecular switches that are controllable, reversible and readable at molecular level are an essential compo-nent of molecular electronics1 and chemical sensors.2-6 Of particular interest are the molecules which show dramatic and reversible changes in color and/or lumi-nescence in visible spectral region upon exposure to specific substrates. A number of chromophore- spacer-receptor systems that can selectively recognize specific guest molecules at their receptor site and pro-duce measurable col…     

Theoretical study of intermolecular proton transfer reaction in isolated 5-hydroxyisoxazole–water complexes

A systematic investigation in isolated 5-hydroxyisoxazole–water complexes (5-HIO · (H₂O)_nn = 1–3) is performed at the DFT level, employing B3LYP/6-31G(d, p) basis set. Single-point energy calculations are also performed at the MP2 level using B3LYP/6-31G(d, p) optimized geometries and the 6-311++G(d, p) basis set. The computational results show that the keto tautomer K₂ is the most stable isomer in the gas phase, and the tautomer K₁ to be the next most stable tautomer. Hydrogen bonding between HIO and the water molecule(s) will dramatically lower the barrier by a concerted multiple proton transfer mechanism. The proton transfer process of 3WE_cis ↔ 3WK₁ and 2WE_trans ↔ 2WK₂ is found to be more efficient in two tautomerization, and the barrier heights are 7.03 and 14.15 kcal/mol at B3LYP/6-31G(d, p) level, respectively. However, the proton transfer reaction between E_cis and K₁ cannot happen without solvent-assisted.     

Intramolecular proton transfer induced by divalent alkali earth metal cation in the gas state

Interactions between divalent alkali earth metal (DAEM) ions M (M?Be, Mg, Ca, Sr, Ba) and the second stable glycine conformer in the gas phase, which can transfer into the ground‐state glycine‐M²⁺ (except the glycine–Be²⁺) among each corresponding isomers when these divalent metal ions are bound, are studied at the hybrid three‐parameter B3LYP level with three different basis sets. Proton transfers from the hydroxyl to the amino nitrogen of the glycine without energy barriers have been first observed in the gas phase in these glycine–M²⁺ systems. The interaction between the glycine and these DAEM ions except beryllium and magnesium ion only create an amino hydrogen pointing to the original hydroxyl due to their weaker interaction relative to those divalent transition metal (DTM) ion‐bound glycine derivatives, being obviously different from that between the glycine and DTM ions, in which two amino hydrogens point to the original hydroxyl oxygen when these metal‐chelated glycine derivatives are produced. The interaction energy between the glycine and divalent magnesium would be the boundary of one or two amino hydrogens pointing to the hydrogyl oxygen, i.e., the ?170.3 kcal/mol of binding energy is a critical point. Similar intramolecular proton transfer has also been predicted for those DTM ion‐chelated glycine systems; however, that in the gas state has not been observed in the monovalent metal ion‐coordinated glycine systems. The binding energy between some monovalent TM ion and the glycine is similar to that of the glycine–Ba²⁺, which has the lowest binding strength among these DAEM–ion chelated glycine complexes. The difference among them only lies in the larger electrostatic and polarized effects in the latter, which favor the stability of the zwitterionic glycine form in the gas phase. According to these observations, we predict that the zwitterionic glycine would exist in the field of two positive charges in the gas phase. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 205–214, 2003     

On the mechanism of proton transfer in imidazole

The force fields, in-plane vibrations, and relative intensities of Raman spectra have been calculated and analyzed for the N₁H and N₃H tautomers of imidazole, imidazolium cation, and their model structures. The results obtained for the isolated state of imidazole correspond to the intramolecular mechanism of proton transfer.     

Weak dihydrogen bond interactions in organic crystals

Database analysis on H ? H interactions of the type CH₂ ? H₂C and N-H ? H-N in organic crystals substantiate the occurrence of dihydrogen bonds in the absence of metal atoms.     

The MNDO-PM3 study of the mechanism of nucleophilic substitution of the phenoxide anion for the nitro group in 1,3,5-trinitrobenzene and 2,4,6-trinitrotoluene in the gas phase and in polar solvents

The semi-empirical quantum chemical MNDO-PM3 calculations of the enthalpies of formation of Meisenheimerortho- andipso--complexes of 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT) with the phenoxide anion in the gas phase and in water are performed within the framework of the point dipole model. Based on the calculated heats and activation barriers to substitution of the nitro group by the phenoxyl group in TNB and TNT, the possibility of the reactions of TNB and TNT with the phenoxide anion in water is shown. These reactions in water occurvia the S_NAr mechanism involving the correspondingipso--complex as an intermediate. In the gas phase, the S_NAr mechanism is impossible, because the reaction is strongly endothermic. In the case of TNT, the exothermic reaction of elimination of a proton from the methyl group by the phenoxide anion competes with nucleophilic substitution in a polar solvent. The activation energy calculated for this exothermic reaction is 8 kcal mol^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 624–628, April, 1995.     

Crystal structure and photochromism of 1-phenyl-3-methyl-4-benzyl-5-one-pyrazole S-methyl thiosemicarbazone

A new organic photochromic compound containing pyrazolone-ring photochromic functional unit: 1-phenyl-3-methyl-4-benzyl-5-one pyrazole S-methyl thiosemicarbazone (PMBP-smtsc) was synthesized. The photochromic properties and photochemical kinetics of PMBP-smtsc have been studied by UV reflectance spectra under irradiation of 365 nm light. The crystal structure analyses of photocolored product show the photochromism is due to the photoisomerization from enol form to keto form through an intermolecular proton transfer.