Multivariate analysis of data for the ionization of weak acids in water – dimethyl sulfoxide solvent mixtures

151

. 61, 2225 (1983).The subject of acidity functions is reviewed, with emphasis on rnodcrn developrncnts. H o and othcr scales determined in acid media, using the Hammett cancellation assumption (zero'th order approximation) are discussed bricfly. The extension to strongly basic systems is also documcnted. Literature references to acidity function scalcs in aqueous acid, aqueous acidlorganic solvcnt, and aqueous base media are tabulated, togcther with those in aqueous baselorganic solvent mixtures at both variable and fixed base concentration. Over 400 acidity functions are referenced, including several electrochemical scales. Various approaches to developing universal functions from the data are discussed. Proton activity scales, based on the Yates-McClelland method of pKBH+ determination, and on electrochemical HoF scales, are prominent among these. Carpentier's method is mentioned, and the first-order approximation, assumed linearity among log activity coefficient ratios, is used to introduce the Bunnett-Olsen and excess acidity (X-function) methods. A brief critical discussion of which method to use is provided. Future developments anticipate the second-order approximation, with a quadratic dependence of log ionization ratios upon X-functions. The review cites 337 individual references. [Traduit par le journal]

Section: Second-order Approximationmentioning

confidence: 99%

“…i~ndoubtedly shows that even the firstorder approximation is, in the limit, inaccurate. Indicated was a quadratic term (280); in the language of the excess acidity method this woulcl necessitate an expansion of eq. 1231 to eq.…”

Section: Second-order Approximationmentioning

confidence: 99%

Acidity functions: an update

Cox¹,

Yates²

1983

151

“…This approach has previously been used, for instance, by Edward et a / . to investigate the complexity of the ionization of weak acids (15) and other interesting systems (16).…”

Section: Discussionmentioning

confidence: 99%

Principal property values for six non-natural amino acids and their application to a structure–activity relationship for oxytocin peptide analogues

Wold¹,

Eriksson²,

Hellberg³

et al. 1987

Self Cite

. Can. J. Chem. 65, 1814Chem. 65, (1987. Previously derived principal property scales for the 20 coded amino acids have been extended to six noncoded amino acids, namely ornithine, norvaline, norleucine, 0-methylated threonine, a-amino butyric acid, and citrulline. This has been done first, for the 20 coded amino acids, by developing PLS models for the relations between the previously derived scales (z, , z 2 , and z3) and newly measured thin-layer chromatography data, proton nuclear magnetic resonance data, plus literature data describing amino acid "bulk" (van der Waals volume and molecular mass). Thereafter, z values for the noncoded amino acids were calculated by inserting the same measured data for these compounds into the PLS models. As a validation, the calculated z values were then used to describe the structural variation of a set of 60 oxytocin peptide analogues for which literature data on biological measurements existed. The models explain 7 1-81% of the variance of the biological data and are highly significant according to cross-validation. Prediction errors of about twice the estimated biological measurement error are obtained for the 11 peptide analogues containing noncoded amino acids. Chem. 65, 1814Chem. 65, (1987.Des Cchelles de propriCtCs principales qui avaient CtC dCveloppCes antkrieurement pour les 20 acides aminCs codes ont Ct C Ctendues i six acides aminis non-codCs, soit l'ornithine, la norvaline, la norleucine, la thrConine 0-mCthylCe, l'acide a-aminobutyrique et la citrulline. Dans un premier temps, on a dCveloppC des modkles PLS pour les 20 acides aminCs codes en se basant sur les relations entre les Cchelles developpCes anterieurement ( z l , z 2 et z3) et les nouvelles donnCes mesuries par chromatographie en couche mince et par resonance magnktique nuclCaire ainsi que des donnCes de la littCrature dCcrivant le ccvolume~) des acides aminCs (volume de van der Waals et masse molCculaire). Ensuite, on a calculC les valeurs z des acides amines non-codes en insirant les mCmes donnCes pour ces composCs dans les modkles PLS. Afin de valider nos conclusions, on a ensuite utilisC les valeurs z pour dkcrire la variation de structure d'un ensemble de 60 analogues du peptide oxytocine pour lesquels des donnCes relatives aux mesures biologiques existent dans la litttrature. Les modkles expliquent de 7 1 a 81% de la variance des donnCes biologiques et, d'aprks des contre-validations, elles sont trks significatives. Pour 11 des analogues peptidiques contenant des acides aminis qui ne sont pas cod&, on peut prCdire des erreurs qui sont le double de l'erreur CvaluCe pour les mesures biologiques.[Traduit par la revue]

“…Edward et al (9) analyzed some data obtained in aqueous DMSO mixtures, and showed that the first-order approximation was insufficiently accurate in that case. Accordingly the new relation [2] was suggested (7,9). It states that the m* term in eq.…”

Section: Introductionmentioning

confidence: 99%

The hydration parameter and the excess acidity functions in H₂SO₄–H₂O and HClO₄–H₂O media

Traverso¹

1984

PIETRO GIUSEPPE TRAVERSO. Can. J. Chem. 62, 153 ( 1984). Excess acidities, X, for aqueous H'SO, and HCIO, arc derived under conditions of fixed pKBbI+ and 111:' : in both media. and of fixed m* only, and compared among themselves and with newly derived and previous scales obtained without constraint, or with fixed pK,,+ valucs. Analysis shows few or no real diffcrcnces among these scalcs. which means that the equation log I + log C,,+ = pK,H+ + nl:':X applies without the necessity of involving a "second-order" ni*:~"X'terni, at least for thcsc media.PIETRO GIUSEPPE TRAVERSO. Can. J . Chcm. 62, 153 (1984). On a derive les aciditis en exctts, X. dcs milieux aqucux dc HISO, ct de HClO, pour dcs conditions ou le PKRII. ct le III": sont fixes dans les deux milieux ainsi que lorsqu'uniqucnicnt m* est fixit; on compare ccs valeurs cntre clles, avcc Ics nouvellcs itchelles ainsi qu'avec les ancicnnes Cchclles obtenucs sans contraintc ou avcc dcs valcurs fixits de pK,,,. . L'analyse ne rkvhle que peu ou pas de diffkrence riellc parmi ccs Cchcllcs. ce qui signifie quc I'itquation log I + log CI.,5 = pK,,,t. + tn:%X s'applique sans la nCcessitC dc fairc intcrvcnir un terme du "second dcgrit" I~"""x', au moins pour ccs milicux.ITraduit par Ic journal]