Yulia B. Ivanova

Corrole NH Tautomers: Spectral Features and Individual Protonation

Protonation of a free-base meso-pyrimidinyl-substituted AB(2)-corrole (H(3)AB(2)) in ethanol solution by stepwise addition of sulfuric acid has been studied in the temperature range from 293 to 333 K. The formation rate of protonated species was found to depend profoundly on the temperature at which the titration was undertaken. Two steps in the titration curve were identified at temperatures around 293-298 K, whereas one-step formation of protonated species was found to occur at temperatures above 308 K. The protonation product was the same in both cases, i.e., H(4)AB(2)(+) corrole, protonated at the macrocycle core nitrogen atoms. The two steps in the protonation kinetics at lower temperatures were attributed to protonation of individual tautomers of the free-base H(3)AB(2) corrole. To the best of our knowledge, this is the first well-illustrated (spectrophotometric) observation of individual properties of corrole NH tautomers in fluid solution. Concomitant increase in the NH tautomerization rate with increasing temperature is proposed to account for the one-step protonation. Evidences for the role of individual corrole NH tautomers in the protonation process as well as their optical features are discussed based on spectroscopic results and simulation data.

Tetrapyrrolic compounds as hosts for binding of halides and alkali metal cations

In this paper the binding of halides and alkali metal cations with porphyrin hosts is reported. The halide ions are complexed with diprotonated porphyrin macrocycle with high affinity and stable complexes of 1:1 and 1:2 structures with halide ions are formed. Strong (up to 300 times) quenching of the porphyrin fluorescence has been found upon the titration of porphyrin solutions with iodide ions. It was established that both static quenching upon formation of the non-fluorescent complex and dynamic diffusion-controlled quenching took place. It is shown that the halide ions binding isotherms can be linearized with double-logarithmic plots. The alkali metal cations are trapped with mono-meso-arylporphyrins containing a conformationally mobile complexing polyether fragment on the benzene ring with a terminal pyridine ring. The alkali metal cation binding constant depends on the polyether chain length. The five-membered (n = 5) polyether chain provides very high binding selectivity for potassium over lithium or sodium. The potassium complexation constants 3.6 × 105 and 7.2 × 104 M-1 have been obtained for Zn2+ complex and diprotonated porphyrin, respectively. For signaling of the alkali cation complexation, it is proposed to use the binding between the terminal pyridine ring with either the Lewis acidic site (chelated Zn2+ ion) or the diprotonated macrocycle core (H4P2+) acting as salt bridging site.

Acid–base equilibria and coordination chemistry of the 5,10,15,20-tetraalkyl-porphyrins: implications for metalloporphyrin synthesis

A spectrophotometric study of the acid–base equilibria and complexation with metal ions has been carried out for 5,10,15,20-tetrakis(trifluoromethyl)porphine and 5,10,15,20-tetrakis(iso-buthyl)porphine in acetonitrile solutions. Protonation and deprotonation of these porphyrins was found to be stepwise with sequential formation of mono- and doubly protonated/deprotonated species. The overall basicity and acidity constants have been determined. The porphyrin complexation with Zn2+ and Cu2+ ions was studied and the rates constants of the macrocycle metallation have been determined. The structure–property relationship derived from the metal chelation studies and the prospects for the use of the above systems for the design of highly sensitive sensors for metal ions were discussed in detail.

Porphyrin acidity and metal ion coordination revisited: electronic substitution effects

Macrocycle acidity and Zn2+ ion coordination are reported for three porphyrin derivatives which differ in both steric and electronic substitution effects on the macrocycle π-conjugated system. The role of the electronic substitution effects in the macrocycle deprotonation and metal ion chelating was found to be dominating whereas the macrocycle nonplanar distortions contribute to the acidity and metal chelation rate of the studied porphyrins in less extent. The contributions of both resonance and inductive electronic substitution effects have been distinguished based on the relationship between the weighted sum of resonance and inductive Hammett constants and the acidity and metal ion chelation rate.

Fluorescent Properties and Kinetic Rate Constants of some Zn-Tetraarylporphyrins Formation in Acetonitrile

The fluorescence quantum yield of the 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetra(4-OH-phenyl)porphyrin, 5,10,15,20-tetra(4-Cl-phenyl)porphyrin, 5,10,15,20-tetra(4-NH2-phenyl)porphyrin and their complexes with Zn2+ have been determined and the kinetic rate constants of the porphyrins ligands complexation with Zn2+ in acetonitrile have been estimated. It was shown that the substituents on the tetrapyrrolic macrocycle periphery have a strong influence on the fluorescent and coordination properties of the investigated porphyrins.

One approximate solution of the shock deformation problem in a cylindrical nonlinear elastic layer

Application of the ray series method is studied on the example of the one-dimensional problem of the impact load on the boundary of a nonlinear elastic cylindrical layer. Particular attention is paid to the construction of ray series for the shock waves formed within the layer as a result of the interaction of the initial shock waves.

The Evolution Equation for Wave Processes of the Shift Deformation

One-dimensional process of formation and the subsequent motion of a plane transverse shock wave is studied on the basis of solutions of the corresponding nonlinear evolutionary equation. This equation defines behaviour of the solution in front area of wave process and follows from inner series of a matched asymptotic expansions method. A comparative analysis of the volume deformation and forming processes will be carried out and their basic differences are specified. In the capacity of model examples solutions of some concrete boundary value problems of a dynamic shear deformation are observed.