Solvent effects on oxygen-17 chemical shifts in amides. Quantitative linear solvation shift relationships

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dc.contributor.authorDiez, E.en
dc.contributor.authorFabian, J. S.en
dc.contributor.authorGerothanassis, I. P.en
dc.contributor.authorEsteban, A. L.en
dc.contributor.authorAbboud, J. L. M.en
dc.contributor.authorContreras, R. H.en
dc.contributor.authordeKowalewski, D. G.en
dc.date.accessioned2015-11-24T16:47:35Z
dc.date.available2015-11-24T16:47:35Z
dc.identifier.issn1090-7807-
dc.identifier.urihttps://olympias.lib.uoi.gr/jspui/handle/123456789/9208
dc.rightsDefault Licence-
dc.subjectab-initio calculationsen
dc.subjecto-17 nmr-spectroscopyen
dc.subjectacetyl-l-prolineen
dc.subjectbasis-setsen
dc.subjectaqueous-solutionen
dc.subjecthydrationen
dc.subjectformamideen
dc.subjectpeptidesen
dc.subjectcisen
dc.subjectparametersen
dc.titleSolvent effects on oxygen-17 chemical shifts in amides. Quantitative linear solvation shift relationshipsen
heal.abstractA multiple-linear-regression analysis (MLRA) has been carried out using the Kamlet-Abboud-Taft (KAT) solvatochromic parameters in order to elucidate and quantify the solvent effects on the O-17 chemical shifts of N-methylformamide (NMF), N,N-dimethylformamide (DMF), N-methylacetamide (NMA), and N,N-dimethylacetamide (DMA). The chemical shifts of the four molecules show the same dependence (in ppm) on the solvent polarity-polarizability, i.e., -22 pi*. The influence of the solvent hydrogen-bond-donor (HBD) acidities is slightly larger for the acetamides NMA and DMA, i.e., -48 alpha, than for the formamides NMF and DMF, i.e., -42 alpha. The influence of the solvent hydrogen-bond-acceptor (HBA) basicities is negligible for the nonprotic molecules DMF and DMA but significant for the protic molecules NMF and NMA, i.e., -9 beta. The effect of substituting the N-H hydrogen by a methyl group amounts to -5.9 ppm in NMF and 5.4 ppm in NMA. The effect of substituting the O=C-H hydrogen amounts to 5.5 ppm in NMF and 16.8 ppm in DMF. The model of specific hydration sites of amides by I. P. Gerothanassis and C. Vakka [J. Org. Chem. 59, 2341 (1994)] is settled in a more quantitative basis and the model by M. I. Burgar, T. F. St, Amour, and D. Fiat [J. Phys. Chem. 85, 502(1981)] is critically evaluated. O-17 hydration shifts have been calculated for formamide (FOR) by the ab initio LORG method at the 6-31G* level. For a formamide surrounded by the four in-plane molecules of water in the first hydration shell, the calculated O-17 shift change due to the four hydrogen bonds, -83.2 ppm, is smaller than the empirical hydration shift, -100 ppm. The O-17 shift change from each out-of-plane water molecule hydrogen-bonded to the amide oxygen is -18.0 ppm, These LORG results support the conclusion that no more than four water molecules are hydrogen-bonded to the amide oxygen in formamide. (C) 1997 Academic Press.en
heal.accesscampus-
heal.fullTextAvailabilityTRUE-
heal.identifier.primaryDOI 10.1006/jmre.1996.7481-
heal.identifier.secondary<Go to ISI>://A1997WP82000003-
heal.identifier.secondaryhttp://ac.els-cdn.com/S1090780796974819/1-s2.0-S1090780796974819-main.pdf?_tid=5e63a238-3247-11e3-acbe-00000aacb362&acdnat=1381476966_2163f3176903900fcb347184c535ac5d-
heal.journalNameJournal of Magnetic Resonanceen
heal.journalTypepeer reviewed-
heal.languageen-
heal.publicationDate1997-
heal.publisherElsevieren
heal.recordProviderΠανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείαςel
heal.typejournalArticle-
heal.type.elΆρθρο Περιοδικούel
heal.type.enJournal articleen

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