A Spectropotentiometric Study of Association Equilibria of Cationic Acids of Mesoporphyrin IX Dimethyl Ester with Iodide Ions in Acetonitrile

The association equilibrium of porphyrinium ions of mesoporphyrin IX dimethyl ester (H₂MP) with iodide ions in acetonitrile was studied by spectropotentiometric titration. Two associates were revealed: (H₄MP^{2 +})(I^-) and (H₄MP^{2 +})(I^-)₂; the electronic absorption spectra of these species were measured, and their formation constants were determined.     

Underwound DNA under tension: structure, elasticity, and sequence-dependent behaviors

DNA melting under torsion plays an important role in a wide variety of cellular processes. In the present Letter, we have investigated DNA melting at the single-molecule level using an angular optical trap. By directly measuring force, extension, torque, and angle of DNA, we determined the structural and elastic parameters of torsionally melted DNA. Our data reveal that under moderate forces, the melted DNA assumes a left-handed structure as opposed to an open bubble conformation and is highly torsionally compliant. We have also discovered that at low forces melted DNA properties are highly dependent on DNA sequence. These results provide a more comprehensive picture of the global DNA force-torque phase diagram.     

The acid properties of benzodiamyloxyl and thiadiazole porphyrazine derivatives in the H<Subscript>2</Subscript>L-(K[2.2.2])OH-DMSO system

Step acid dissociation reactions of benzodiamyloxyl (X) and thiadiazole (Y) porphyrazine (H₂PA) derivatives H₂PA(X)₄, H₂PA(X)₃(Y), H₂PA(X)₂(Y)₂, H₂PA(X)(Y)₃, and H₂PA(Y)₄ were studied theoretically (MP3) and experimentally (spectropotentiometrically) in the H₂L-(K[2.2.2])OH-DMSO system for the series H₂P (porphin), H₂P(μs-Pr)₄, H₂P(μs-Ph)₄, H(N-Me)P(μs-Ph)₄, H₂TBP (tetrabenzoporphin), H₂TBP(μs-Ph)₄, H₂PA (porphyrazine), H₂PA(β-Ph)₄, H₂PC (phthalocyanine), and H₂PC(t-Bt)₄. The linear correlation pK _a1 ²⁹⁸ = 0.32622ΔH°_a1(g) ? 94.62 (R = 0.998) was observed for H₂PA and its symmetrical derivatives H₂PA(β-Ph)₄, H₂PC, H₂PC(t-Bt)₄, H₂PC(X)₄, and H₂PC(Y)₄. Deviations of the proportionality factors in the pK _a1 ²⁹⁸ = bH°_a1(g) + A dependences from the theoretical value (2.303RT)^?1 were explained by medium effects. Substituent effects on pK _a1 ²⁹⁸ were divided into internal δ(R _i)_int and external δ(R _i)_ext (solvation) contributions. The compensation dependences δ(R _i)_ext = ?0.10911δ(R _i)_int + 0.13 and δ(R _i)_ext = ?0.52969δ(R _i)_int (correlation coefficients 0.998) were observed for simple (H₂PA, H₂TBP, H₂P(μs-Ph)₄, and H₂P(μs-Pr)₄) and complex (H(N-Me)P(Ph)₄, H₂TBP(μs-Ph)₄, H₂PA(β-Ph)₄,H₂PA(Y)₄, H₂PC, H₂PC(t-Bt)₄, and H₂PC(X)₄) porphin derivatives, respectively.     

Lattice statistical model for phase transition of active component of catalyst for SO2 oxidation

The statistical lattice model suggested considers phase transitions in a vanadium catalyst for SO₂ oxidation regarding the real structure of the melt of the active component. The model is proved to reflect properly the experimentally observed regularities, e.g., how V⁴⁺ compounds crystallize from the melt depending on their concentration and reaction temperature.     

Influence of Water on the Equilibria of Protonation of Mesoporphyrin IX Dimethyl Ether in Acetonitrile

The equilibria of protonation of mesoporphyrin IX dimethyl ether (H₂MP), namely, H₂MP + H⁺ H₃MP⁺ and H₃MP⁺ + H⁺ H₄MP²⁺, in the H₂MP(1.4 × 10^–5 mol/l)–HClO₄(0–0.01 mol/l)–H₂O(0.01–1.65 mol/l)–CH₃CN system at 298 K were studied using the spectropotentiometry method. It was established that the first-step equilibrium (logK ₁ = 11.95) is not affected by water. The dication forms two hydrates (H₂O)H₄MP²⁺ and (H₂O)₂H₄MP²⁺ with the step formation constants K _{h 1} = 8.50 and K _{h 2} = 1.39. The conventional constant of the second protonation step is related to the water concentration through the equation logK ₂ ^" = logK ₂ + log(1 + K _{h 1}[H₂O] + K _{h 1} K _{h 2}[H₂O]²). In anhydrous acetonitrile, logK ₂ = 7.51. The electronic absorption spectra of H₄MP²⁺ and of its hydrates are identical; therefore, K ₁ and K ₂ ^" cannot be distinguished in photometric determination of [H₄MP²⁺] in the presence of water.     

Porphyrin halide ion receptor

Formation of 1:1 and 1:2 complexes of mono-and dications of octaalkylporphyrin with halide ions in acetonitrile at 298 K was studied by spectropotentiometric titration. The stability constants of the complexes were determined.     

Synthesis and spectral characteristics of (tetrabenzoporphyrinato)chloromanganese(III)

A method is developed of synthesis of (tetrabenzoporphyrinato)chloromanganese(III) from tetrabenzoporphyrinatocadmium( II) (as a donor of the macrocyclic ligand) and the salts, manganese acetate MnAc2 and dichloromanganese MnCl2, in boiling dimethylformamide in the presence of atmosperic oxygen in 80% yield. It is found that under the conditions of the synthesis tetrabenzoporphyrinatomanganese(II) is formed which can be oxidized by the atmospheric oxygen to (tetrabenzoporphyrinato)chloromanganese(III). Absorption spectra in the visible and infrared regions, R _f and the data of elemental analysis characterizing the resulting compound are given.     

Theoretical and Experimental Study of the Effect of Tetra-β-phenyl Substitution on the Acid-Base Properties of Porphyrazine

The effect of tetra-β-phenyl substitution on the acid-base properties of the porphyrazine macroring was studied by theoretical and experimental methods.     

Halide ion determination from luminescence of the diprotonated form of porphyrin

We have studied quenching of the fluorescence of the diprotonated form of 3,7,13,17-tetramethyl-2,8,12,18-tetrabutylporphyrin by iodide ions in solutions. We have established that there is both static quenching of fluorescence when nonfluorescent complexes are formed with the iodide ions, as a result of an internal heavy atom effect, and also dynamic diffusion-controlled quenching. Based on analysis of the dependences of the fluorescence intensity and fluorescence lifetime on the iodide ion concentration in solution, we suggest using the diprotonated form of this porphyrin as the base compound for designing a fluorescent molecular receptor for halide ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 750–755, November–December, 2007.