On Some Extremal Properties of Finite Ultrametric Spaces

We characterize finite ultrametric spaces having the strictly n-ary representing trees and finite ultrametric spaces having the representing trees with injective internal labelings by their extremal properties.     

Heterogeneous Wide Range <Emphasis Type=Italic>pH</Emphasis>-sensing Materials Allowing Ratiometric Fluorescence Detection Based on Structurally Rigid Analogs of 2,6-distyrylpyridine

The new sensing materials based on the microsized silica gel powder with non-covalently immobilized structurally rigid analogs of 2,6-distyrylpyrydine ((3E,5E)-3,5-dibenzylidene-8-phenyl-1,2,3,5,6,7-hexahydrodicyclopenta[b,e]pyridines) were developed and tested. Most of the investigated compositions demonstrate linear ratiometric fluorescence response on pH in the physiologically important interval (pH 6–9). The compound with the greatest number of protolytic centers within the studied series demonstrated the widest pH sensitivity range, however in this case the analytical signal was the lowest. The prospects for the practical application of the investigated materials in the fiber optics sensing devices were outlined.     

Heterometallic M/Mn (M=Cu, Co, Zn) acetate complexes as precursors for binary oxides

A facile one-pot procedure, or so-called “direct synthesis,” was used to prepare the novel heterometallic complexes [M₂Mn(OAc)₆(bpy)₂], where M=Cu (1), Co (2), Zn (3), bpy=2,2′-bipyridyl, with high yields via oxidative dissolution of pure metals in a liquid phase. The complexes were characterized by an elemental analysis, single crystal X-ray diffraction method and FTIR. These complexes are proposed as precursors, whose thermal degradation may lead to the formation of solids possessing nano- to microsize levels of dispersity. The thermal behavior of the complexes obtained was studied by thermal analysis (TG/DTA/DTG) in both air and N₂ and also by TPD mass-spectrometry in vacuo. The FTIR, X-ray powder diffraction (PXRD) and thermoanalytical data were used for the identification of the solid products of thermal degradation. The morphology and microstructure of the solid residues were analyzed, using scanning electron microscopy with energy dispersive X-ray microanalysis (SEM/EDX) at mkm and sub-micro levels.     

Dependence of the anticancer activity of 1,3‐oxazole derivatives on the donor/acceptor nature of his substitues

A series of new 1,3‐oxazole derivatives, containing in position 5 both donor and acceptor substituents were synthesized. These substances were considered as potentially active anticancer pharmacophores in the human tumor cell line panel derived from nine cancer types, including lung, colon, melanoma, renal, ovarian, brain, leukemia, breast, and prostate. Primary in vitro one‐dose anticancer screening was shown that compounds with acceptor substituents (such as –C(O)OMe, –CN) in the position 5 inhibit the growth of most cell lines, and compounds with donor substituents (such as –NHR, ?SR) in the position 5 do not practically inhibit the growth of cancer cell lines. It can be assumed that the pharmacological activity of 1,3‐oxazole derivatives depends on donor/acceptor nature of the substituents in position 5. It was proposed to evaluate the donor/acceptor ability of 1,3‐oxazole derivatives using the special parameter φ₀, which takes into account the relative position of the boundary levels (HOMO end LUMO). The quantum‐chemical modeling was performed; the special parameter φ₀ for 1,3‐oxazole derivatives correlates with the experimental results. Quantum‐chemical calculations of the special parameter φ₀ allow modeling the pharmacological activity of 1,3‐oxazole derivatives by introducing donor or acceptor substituents at position 2 or 5. This work may be useful for chemists to develop a target synthesis of potential biologically active compounds.     

Visible-light photocurrent response of TiO2-polyheptazine hybrids: evidence for interfacial charge-transfer absorption

We investigated photoelectrodes based on TiO(2)-polyheptazine hybrid materials. Since both TiO(2) and polyheptazine are extremely chemically stable, these materials are highly promising candidates for fabrication of photoanodes for water photooxidation. The properties of the hybrids were experimentally determined by a careful analysis of optical absorption spectra, luminescence properties and photoelectrochemical measurements, and corroborated by quantum chemical calculations. We provide for the first time clear experimental evidence for the formation of an interfacial charge-transfer complex between polyheptazine (donor) and TiO(2) (acceptor), which is responsible for a significant red shift of absorption and photocurrent response of the hybrid as compared to both of the single components. The direct optical charge transfer from the HOMO of polyheptazine to the conduction band edge of TiO(2) gives rise to an absorption band centered at 2.3 eV (540 nm). The estimated potential of photogenerated holes (+1.7 V vs. NHE, pH 7) allows for photooxidation of water (+0.82 V vs. NHE, pH 7) as evidenced by visible light-driven (λ > 420 nm) evolution of dioxygen on hybrid electrodes modified with IrO(2) nanoparticles as a co-catalyst. The quantum-chemical simulations demonstrate that the TiO(2)-polyheptazine interface is a complex and flexible system energetically favorable for proton-transfer processes required for water oxidation. Apart from water splitting, this type of hybrid materials may also find further applications in a broader research area of solar energy conversion and photo-responsive devices.     

The synthesis of a 2-azabicyclo[3.1.0]hexane by rearrangement of a spirocyclic epoxide

An unusual rearrangement of a 1-oxa-6-azaspiro[2.5]octane derivative giving access to novel 5-substituted 2-azabicyclo[3.1.0]hexanes is described. The synthetic application of the reaction is demonstrated by the synthesis of N-Boc-2,3-methano-β-proline. The amino acid was prepared through a three-step synthesis from easily available reagents in an overall yield of 15%.     

Theoretical study of the EE reaction mechanism with comproportionation and different diffusivities of reactants

In this article we investigate the origin of unexpected features appearing in voltammetry or double-step chronoamperometry of EE systems when the rate of comproportionation is extremely fast and the diffusion coefficients of the reactant and products highly differ. These features were noticed during the testing of our new software KISSA intended to solve any reaction mechanisms even when acute reaction fronts develop near the electrode surface or within the solution. To validate the principle of the new adaptive algorithm [C. Amatore, O. Klymenko, I. Svir, Electrochem. Commun. doi:10.1016/j.elecom.2010.06.009] implemented in KISSA we used analytical and numerical solutions for double-step chronoamperometry. This revealed that the peculiar current jumps stem from a rapid variation of the reaction front position when the starting material is still reducible at the electrode while the product of the second electron transfer is re-oxidized. The exact convergence between the predictions by these independent methods demonstrated that KISSA is perfectly accurate even under such extreme mechanistic conditions.     

Reactions at the solid-liquid interface: surface-controlled dissolution of solid particles. The dissolution of potassium bicarbonate in dimethylformamide

We present a mathematical model for the surface-controlled dissolution of solid particles. This is applied to the dissolution of a solid having different particle size distribution functions: those of a monodispersed solid containing particles of all one size, a two-size-particle distribution, and a Gaussian distribution of the particle sizes. The dissolution of potassium bicarbonate in dimethylformamide is experimentally studied indirectly at elevated temperatures. We monitor the dissolution via the homogeneous deprotonation of 2-cyanophenol by dissolved KHCO3. The loss of 2-cyanophenol was detected electrochemically at a platinum microdisk electrode, and separately, the formation of the 2-cyanophenolate anion was monitored via UV-visible spectroscopic analysis. The results presented show that the kinetics of the loss of 2-cyanophenol behaves on one hand as a homogeneous chemical process and on the other hand as a dissolution-rate-controlled process. Initially, predissolved KHCO3 in solution deprotonates the 2-cyanophenol and homogeneous reaction dominates the observed kinetics, and at longer times, the observed kinetics is controlled by the rate of KHCO3 dissolution. Modeling of the experimental results for the surface-controlled dissolution of KHCO3 in dimethylformamide (DMF) yielded a mean value for the dissolution rate constant, k, at elevated temperatures; k was found to have a value of (1.1 +/- 0.3) x 10(-8) mol cm(-2) s(-1) at 100 degrees C, and the activation energy for the dissolution was 34.4 +/- 0.4 kJ mol(-1) over the temperature range 60-100 degrees C.     

Postsynthesis transformation of three-dimensional framework into a lamellar zeolite with modifiable architecture

Mild treatment of zeolite UTL results in degradation of its structure with preservation of the initially present dense layers connected by D4R "bridges". The lamellar product obtained through this 3D to 2D zeolite conversion has been structurally modified similar to methodologies applied to layered zeolite precursors, which show the opposite 2D to 3D zeolite transformation.