Article

1998 ◽  
Vol 76 (5) ◽  
pp. 576-582
Author(s):  
Patricia Gabriela Molina ◽  
María Alicia Zón ◽  
Héctor Fernández
Keyword(s):  
Dissociation Constants ◽  
Monomethyl Ether ◽  
Spectroscopic Studies ◽  
Acid Dissociation ◽  
Alternariol Monomethyl Ether ◽  
Acid Dissociation Constants ◽  
Ph Values ◽  
Acidic Constant ◽  
Acidic Constants ◽  
Good Agreement

The acid dissociation constants for alternariol monomethyl ether (AME), altertoxin-I (ATX-I), and alternariol (AOH), three of the Alternaria alternata genus mycotoxins, are estimated through conventional UV-VIS spectroscopic studies at different pH values. Experimental variations of absorbance as a function of pH at a given wavelength were fitted by using the exact equations that describe the systems studied. Good agreement between the experimental absorbance vs. pH plots and the curves generated by the fitting process was found. A comparison between the acidic constants for the first step of dissociation of these mycotoxins and the value for the acidic constant of phenol is discussed by assuming that phenolic structures are responsible for the acidity of these mycotoxins.Key words: mycotoxins, alternariol monomethyl ether, altertoxin-I, alternariol, acidic constants.

Decomposition of some cyclic dithiocarbamates

1970 ◽  
Vol 48 (14) ◽  
pp. 2204-2209 ◽  
Author(s):  
Ronald R. Vandebeek ◽  
Serge J. Joris ◽  
Keijo I. Aspila ◽  
Chuni L. Chakrabarti
Keyword(s):  
Dielectric Constant ◽  
Dissociation Constants ◽  
Acid Dissociation ◽  
Acid Molecule ◽  
Decomposition Rates ◽  
Acid Dissociation Constants ◽  
Ring Strain ◽  
Relative Stabilities ◽  
Ph Values ◽  
The Stability

The stability of some cyclic N,N-disubstituted dithiocarbamates has been studied by the analysis of the decomposition rates at different pH values. It is concluded that the most important factors which determine the relative stabilities of three cyclic dithiocarbamates (DTC) are the solvation of the DTC acid molecule and the ring strain associated with the substituents. This has been proven by a study of (a) the decomposition rates as a function of the dielectric constant of the medium, (b) order of the stability, and (c) activation energy.The molar absorptivities and the apparent acid dissociation constants have been determined for pyrrolidine-, piperidine-, and hexamethylene-dithiocarbamates.

Pyridine nitrosazones and their cobalt(III) chelates

1977 ◽  
Vol 55 (21) ◽  
pp. 3707-3711 ◽  
Author(s):  
Ahmad Sami Shawali ◽  
Ikhlass M. Abbass
Keyword(s):  
Ionic Strength ◽  
Spectral Data ◽  
Dissociation Constants ◽  
Ring Structure ◽  
Membered Ring ◽  
Acid Dissociation ◽  
Acid Dissociation Constants ◽  
Transition Energies ◽  
Amyl Nitrite ◽  
Good Agreement

Nitrosation of pyridine aldehyde p-tolylhydrazones 2 with amyl nitrite gives rise to p-tolueneazopyridine aldoximes 4 which form stable tris chelates with cobalt(III). Spectral data (ir, uv, and 1Hmr) indicate that the ligands exist mainly in the assigned azooxime structure 4, and that their chelates have five-membered ring structure 7. Also, the 1Hmr spectra imply mer-configuration 9 for the chelates examined. No evidence for the tautomeric nitrosohydrazone structure 3 for the ligands and the fac-configuration 8 for Co(III) chelates could be obtained. Using the HMO method, the azooxime form 4 for the ligand was shown to be more stable than the nitrosohydrazone structure 3. Also, good agreement was obtained between observed transition energies and those calculated by the HMO method. The acid dissociation constants of the ligands in 50 vol% ethanol–water at 25 °C and ionic strength of 0.1 were determined spectrophotometrically.

Solution speciation in the aqueous Na(I)–EDTA and K(I)–EDTA systems

1993 ◽  
Vol 71 (5) ◽  
pp. 763-768 ◽  
Author(s):  
Min Chen ◽  
R. Stephen Reid
Keyword(s):  
Potentiometric Titration ◽  
Ethylenediaminetetraacetic Acid ◽  
Dissociation Constants ◽  
Equilibrium Constants ◽  
Acid Dissociation ◽  
Equilibrium Models ◽  
Acid Dissociation Constants ◽  
Aqueous Sodium ◽  
Ph Values ◽  
Solution Speciation

Speciation in the aqueous sodium(I) – ethylenediaminetetraacetic acid and potassium(I) – ethylenediaminetetraacetic acid equilibrium systems was investigated by automated gravimetric potentiometric titration. It was found that in both cases, particularly below neutral pH values, speciation includes a previously uncharacterized diprotonated complex. All formation and acid dissociation constants were measured for the full systems. The validity of previous literature equilibrium constants, which are based on incomplete equilibrium models, is discussed.

Calculation of reference pH values for standard solutions from the corresponding acid dissociation constants

1990 ◽  
Vol 239 ◽  
pp. 129-137 ◽  
Author(s):  
M.J.Guiomar H.M. Lito ◽  
M.Filomena G.F.C. Camões ◽  
M.Isabel A. Ferra ◽  
Arthur K. Covington
Keyword(s):  
Dissociation Constants ◽  
Acid Dissociation ◽  
Acid Dissociation Constants ◽  
Ph Values ◽  
Standard Solutions
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