Solvent effects on oxygen-17 chemical shifts in amides. Quantitative linear solvation shift relationships
Φόρτωση...
Ημερομηνία
Συγγραφείς
Diez, E.
Fabian, J. S.
Gerothanassis, I. P.
Esteban, A. L.
Abboud, J. L. M.
Contreras, R. H.
deKowalewski, D. G.
Τίτλος Εφημερίδας
Περιοδικό ISSN
Τίτλος τόμου
Εκδότης
Elsevier
Περίληψη
Τύπος
Είδος δημοσίευσης σε συνέδριο
Είδος περιοδικού
peer reviewed
Είδος εκπαιδευτικού υλικού
Όνομα συνεδρίου
Όνομα περιοδικού
Journal of Magnetic Resonance
Όνομα βιβλίου
Σειρά βιβλίου
Έκδοση βιβλίου
Συμπληρωματικός/δευτερεύων τίτλος
Περιγραφή
A 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.
Περιγραφή
Λέξεις-κλειδιά
ab-initio calculations, o-17 nmr-spectroscopy, acetyl-l-proline, basis-sets, aqueous-solution, hydration, formamide, peptides, cis, parameters
Θεματική κατηγορία
Παραπομπή
Σύνδεσμος
<Go to ISI>://A1997WP82000003
http://ac.els-cdn.com/S1090780796974819/1-s2.0-S1090780796974819-main.pdf?_tid=5e63a238-3247-11e3-acbe-00000aacb362&acdnat=1381476966_2163f3176903900fcb347184c535ac5d
http://ac.els-cdn.com/S1090780796974819/1-s2.0-S1090780796974819-main.pdf?_tid=5e63a238-3247-11e3-acbe-00000aacb362&acdnat=1381476966_2163f3176903900fcb347184c535ac5d
Γλώσσα
en
Εκδίδον τμήμα/τομέας
Όνομα επιβλέποντος
Εξεταστική επιτροπή
Γενική Περιγραφή / Σχόλια
Ίδρυμα και Σχολή/Τμήμα του υποβάλλοντος
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας