Axial coordination reactions with nitrogenous bases and determination of equilibrium constants for zinc tetraarylporphyrins containing four β,β′-fused butano and benzo groups in nonaqueous media

2021 ◽  
pp. 1279-1288
Author(s):  
Lina Ye ◽  
Yuanyuan Fang ◽  
Zhongping Ou ◽  
Liping Wang ◽  
Songlin Xue ◽  
...  
Keyword(s):  
Equilibrium Constants ◽  
Nonaqueous Media ◽  
Axial Coordination

Axial coordination reactions with nitrogenous bases and determination of equilibrium constants for zinc tetraarylporphyrins containing four β,β′-fused butano and benzo groups in nonaqueous media

2019 ◽  
Vol 23 (01n02) ◽  
pp. 196-205 ◽  
Author(s):  
Lina Ye ◽  
Yuanyuan Fang ◽  
Zhongping Ou ◽  
Liping Wang ◽  
Songlin Xue ◽  
...  
Keyword(s):  
Dissociation Constants ◽  
Equilibrium Constants ◽  
Acid Dissociation ◽  
Nonaqueous Media ◽  
Acid Dissociation Constants ◽  
Axial Coordination ◽  
Conjugate Acid ◽  
Nitrogenous Base ◽  
Spectral Titration

The axial coordination properties of six zinc tetraarylporphyrins with seven different nitrogenous bases were examined in CH2Cl2 for derivatives containing four [Formula: see text],[Formula: see text]-fused butano or benzo groups and the equilibrium constants (log[Formula: see text] determined using spectral titration methods. The examined compounds are represented as butano(YPh)4PorZn and benzo(YPh)4PorZn, where Por is the porphyrin dianion and Y is a CH3, H or Cl substituent on the para-position of each meso-phenyl ring of the macrocycle. The initial four-coordinate butano- and benzoporphyrins will axially bind one nitrogenous base to form five-coordinate derivatives in CH2Cl2 and this leads to a 4–22 nm red-shift of the Soret and Q bands. The log[Formula: see text] values range from 1.98 to 4.69 for butano(YPh)4PorZn and from 3.42 to 5.36 for benzo(YPh)4PorZn, with the exact value depending upon the meso and [Formula: see text]-substituents of the porphyrin and the conjugate acid dissociation constants (p[Formula: see text] of the nitrogenous base.

N-confusedmeso-tetraaryl-substituted free-base porphyrins: determination of protonation and deprotonation constants in nonaqueous media

2015 ◽  
Vol 19 (01-03) ◽  
pp. 251-260 ◽  
Author(s):  
Zhongping Ou ◽  
Xueyan Chen ◽  
Lina Ye ◽  
Songlin Xue ◽  
Yuanyuan Fang ◽  
...  
Keyword(s):  
Tautomeric Form ◽  
Equilibrium Constants ◽  
Single Step ◽  
Free Base ◽  
Nonaqueous Media ◽  
Tautomeric Forms ◽  
Visible Spectra ◽  
Phenyl Rings ◽  
Uv Visible

The protonation and deprotonation reactions for a series N-confused meso-tetraaryl-substituted free-base porphyrins containing electron-donating or electron-withdrawing substituents was monitored in CHCl3and DMF by UV-visible spectroscopy during titrations with trifluoroacetic acid or tetra-n-butylammonium hydroxide. The spectroscopic data was also used to calculate equilibrium constants for these reactions. The examined compounds are represented as (XPh)4NCPH2, where "NCP" represents the N-confused porphyrin π-conjugated macrocycle and X is a CH3O , CH3, H or Cl para-substituent on the four meso-phenyl rings (Ph) of the compound. The porphyrins can exist in two tautomeric forms depending upon the solvent and each tautomer undergoes two stepwise protonation reactions leading to formation of the mono- and bis-protonated porphyrins, [(XPh)4NCPH3]+and [(XPh)4NCPH4]2+. A single step deprotonation is observed for the same compounds in DMF and the product is assigned as [(XPh)4NCPH]-. Comparisons are made between UV-visible spectra of the protonated, neutral and deprotonated forms of the porphyrin and the effect of the porphyrin ring substituents and tautomeric form of the neutral porphyrin on the UV-visible spectra and protonation constants is discussed along with data from DFT calculations.

Spectrophotometric study of the complexation equilibria of cadmium ions with 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-diethylaminophenol (BrPADAP, ClPADAP)

1983 ◽  
Vol 48 (1) ◽  
pp. 52-59 ◽  
Author(s):  
Vlastimil Kubáň ◽  
Miroslav Macka
Keyword(s):  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Graphical Analysis ◽  
Optimal Conditions ◽  
Cadmium Ions ◽  
Brij 35 ◽  
Ethanol Medium ◽  
Triton X ◽  
Derivatives Of

The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the reactions of formation of the ML and ML2 complexes of both reagents with cadmium(II) ions were determined by graphical analysis and numerical interpretation of the absorbance-pH curves by the modified SQUAD-G program. Optimal conditions were proposed for the spectrophotometric determination of Cd in 10% v/v ethanol medium in the presence of 0.1% w/v Triton X-100 or 1% w/v Brij 35. BrPADAP and ClPADAP are the most sensitive spectrophotometric reagents for the determination of cadmium(II) ions (ε = 1.28-1.44 . 105 mmol-1 cm2 at 560 nm and pH 8.0-9.5) with a high colour contrast in the reaction (Δλmax ~117 nm) and a selectivity similar to that of other N-heterocyclic azodyes (PAR, PAN, etc.).

Spectrophotometric study of the acid-base and optical properties of the 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-(diethylamino)phenol (BrPADAP, ClPADAP) and their complexation equilibria with zinc(II) ions

1982 ◽  
Vol 47 (10) ◽  
pp. 2676-2691 ◽  
Author(s):  
Miroslav Macka ◽  
Vlastimil Kubáň
Keyword(s):  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Graphical Analysis ◽  
Alkaline Media ◽  
Acid Base ◽  
Ethanol Medium ◽  
Triton X ◽  
Mixed Water ◽  
Derivatives Of

The optical and acid-base characteristics of BrPADAP and ClPADAP were studied in mixed water-ethanol and water-DMF media and in 10% ethanol medium in the presence of cationic, anionic and nonionic tensides. The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the ML and ML2 complexes with zinc(II) ions were found by graphical analysis and numerical interpretation of the absorbance curves by the modified SQUAD-G program. Optimal conditions were found for the spectrophotometric determination of Zn(II) in the presence of 0.1% Triton X-100 or 1% Brij 35 in alkaline media with pH = 6.5-10. BrPADAP and ClPADAP are the most sensitive reagents (ε = 1.3-1.6 . 105 mmol-1 cm2 at 557 and 560 nm, respectively) for the determination of zinc with high colour contrast of the reaction (Δλ = 104 nm) and selectivity similar to that for the other N-heterocyclic azodyes (PAN, PAR, etc.).

scholarly journals Recognition of hydrogen isotopomers by an open-cage fullerene

2013 ◽  
Vol 371 (1998) ◽  
pp. 20110629 ◽  
Author(s):  
Yasujiro Murata ◽  
Shih-Ching Chuang ◽  
Fumiyuki Tanabe ◽  
Michihisa Murata ◽  
Koichi Komatsu
Keyword(s):  
Equilibrium Constants ◽  
Equilibrium Mixture ◽  
Size Difference ◽  
Binding Affinities ◽  
Kinetic Isotope ◽  
Molecular Sizes ◽  
Lower Temperature ◽  
Kinetics Of ◽  
Pressure Hydrogen

We present our study on the recognition of hydrogen isotopes by an open-cage fullerene through determination of binding affinity of isotopes H 2 /HD/D 2 with the open-cage fullerene and comparison of their relative molecular sizes through kinetic-isotope-release experiments. We took advantage of isotope H 2 /D 2 exchange that generated an equilibrium mixture of H 2 /HD/D 2 in a stainless steel autoclave to conduct high-pressure hydrogen insertion into an open-cage fullerene. The equilibrium constants of three isotopes with the open-cage fullerene were determined at various pressures and temperatures. Our results show a higher equilibrium constant for HD into open-cage fullerene than the other two isotopomers, which is consistent with its dipolar nature. D 2 molecule generally binds stronger than H 2 because of its heavier mass; however, the affinity for H 2 becomes larger than D 2 at lower temperature, when size effect becomes dominant. We further investigated the kinetics of H 2 /HD/D 2 release from open-cage fullerene, proving their relative escaping rates. D 2 was found to be the smallest and H 2 the largest molecule. This notion has not only supported the observed inversion of relative binding affinities between H 2 and D 2 , but also demonstrated that comparison of size difference of single molecules through non-convalent kinetic-isotope effect was applicable.

A Potentiometric Study on Proton-Transfer Equilibria and Cationic Conjugation in Pyridine N-Oxide Systems in Acetone and Methanol

1996 ◽  
Vol 49 (9) ◽  
pp. 931 ◽  
Author(s):  
L Chmurzynski ◽  
E Kaczmarczyk ◽  
M Nesterowicz ◽  
G Wawrzyniak ◽  
Z Warnke
Keyword(s):  
Proton Transfer ◽  
Equilibrium Constants ◽  
Proton Donor ◽  
Heterocyclic Amines ◽  
Transfer Reactions ◽  
Oxide Systems ◽  
Experimental Systems ◽  
Proton Transfer Reactions ◽  
Potentiometric Titration Method

The potentiometric titration method has been used to study the equilibria of cationic in sytems formed by substituted pyridine N-oxides in the polar, non-aqueous solvents acetone and methanol. For comparison, the systems with trimethylamine N-oxide as a representative of aliphatic amine N-oxides and pyridine representing parent heterocyclic amines were also studied. The cationic heteroconjugation constants, i.e. the equilibrium constants for conjugation reactions between free and protonated N-bases leading to the formation of unsymmetric BHB'+ cations, were determined in experimental systems with and without proton transfer. It was found that there were significant differences in the values of the cationic heteroconjugation constants determined in these two acid-base systems. The proton-transfer reactions limit and even preclude the determination of the cationic heteroconjugation constants. On this basis it was concluded that the heteroconjugation constants should be determined in systems without proton transfer. In such systems, in the amphiprotic solvent methanol, cationic heteroconjugation was ascertained in all substituted pyridine N-oxide systems, the values of heteroconjugation constants being relatively low (logarithms of their values of the order of 2-2.5), and only negligible in systems involving trimethylamine N-oxide. A more pronounced tendency towards cationic heteroconjugation of the [OHO]+ type was observed in the aprotic protophobic acetone, where heteroconjugation constants were determined for all amine N-oxide systems studied including those containing protonated trimethylamine N-oxide as a proton donor. However, the values of the cationic heteroconjugation constants were found to be, in methanol likewise, relatively low (log KBHB'+ of the order of 2-3). On the contrary, a greater extent of cationic heteroconjugation equilibria was observed in methanol than in acetone in the case of systems containing pyridine, i.e. [NHO]+ type bridges formed by amine N-oxides and heterocyclic amines. In methanol the heteroconjugation constants turned out to be determinable for all such systems studied (logarithms of the equilibrium constants being of the same order as for N-oxide systems), whereas in acetone the hetero constants were indeterminable for all systems.

The experimental determination of hydromagnesite precipitation rates at 22.5–75ºC

2014 ◽  
Vol 78 (6) ◽  
pp. 1405-1416 ◽  
Author(s):  
U.-N. Berninger ◽  
G. Jordan ◽  
J. Schott ◽  
E. H. Oelkers
Keyword(s):  
Low Temperature ◽  
Experimental Determination ◽  
Closed System ◽  
Equilibrium Constants ◽  
Magnesium Silicate ◽  
Silicate Mineral ◽  
Dissolution Rates ◽  
Dissolution And Precipitation

Natural hydromagnesite (Mg5(CO3)4(OH)2·4H2O) dissolution and precipitation experiments were performed in closed-system reactors as a function of temperature from 22.5 to 75ºC and at 8.6 < pH < 10.7. The equilibrium constants for the reaction Mg5(CO3)4(OH)2·4H2O + 6H+ = 5Mg2+ + 4HCO3– + 6H2O were determined by bracketing the final fluid compositions obtained from the dissolution and precipitation experiments. The resulting constants were found to be 1033.7±0.9, 1030.5±0.5 and 1026.5±0.5 at 22.5, 50 and 75ºC, respectively. Whereas dissolution rates were too fast to be determined from the experiments, precipitation rates were slower and quantified. The resulting BET surface areanormalized hydromagnesite precipitation rates increase by a factor of ~2 with pH decreasing from 10.7 to 8.6. Measured rates are approximately two orders of magnitude faster than corresponding forsterite dissolution rates, suggesting that the overall rates of the low-temperature carbonation of olivine are controlled by the relatively sluggish dissolution of the magnesium silicate mineral.

Electrochemical and binding properties of a meso-tetra(4-pyridyl)porphyrinatozinc supermolecule containing four μ3-oxo-triruthenium acetate clusters

2000 ◽  
Vol 04 (08) ◽  
pp. 727-735 ◽  
Author(s):  
SERGIO DOVIDAUSKAS ◽  
KOITI ARAKIA ◽  
HENRIQUE E. TOMA
Keyword(s):  
Equilibrium Constants ◽  
Zinc Ion ◽  
Porphyrin Ring ◽  
Electronic Density ◽  
Axial Coordination ◽  
Spectrophotometric Titrations ◽  
Regular Increase ◽  
Calculated Equilibrium ◽  
C Nmr

The synthesis and characterization of a zinc meso-tetra(4-pyridyl)porphyrin containing four coordinated μ3-oxo-triruthenium acetate cluster complexes, ZnTCP , are reported. The coordination of four ruthenium acetate clusters to the zinc porphyrin has been confirmed by 1 H and 13 C NMR spectroscopy, including COSY and HETCOR bidimensional correlation techniques. Cyclic voltammetry and spectroelectrochemistry studies have revealed the presence of seven redox processes in the −1.5 to 2.5 V range, four of them attributed to cluster-centered ( Ru IV,IV,III/ Ru IV,III,III/ Ru III,III,III/ Ru III,III,II/ Ru III,II,II) and three to porphyrin ring-centered ( ZnP +/ ZnP / ZnP .−/ ZnP 2−) redox reactions. The axial coordination reaction has been monitored by spectrophotometric titrations in dichloromethane and acetonitrile, in the 380–480 nm range, using pyridine, imidazole, water and acetonitrile as ligands. The influence of the peripheral ruthenium complexes on the electronic properties of the porphyrin ring has been assayed by measuring the axial coordination properties of the zinc ion. The calculated equilibrium constants for axial coordination of pyridine and imidazole to ZnTCP in dichloromethane are respectively one and two orders of magnitude higher than for meso-tetraphenylporphyrinatozinc, showing a regular increase as a function of the basicity of the ligands. The results have demonstrated that the Ru (III,III,III) species act as electron-withdrawing groups, decreasing significantly the electronic density on the porphyrin ring.

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