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Solvation effects on the 31 P‐nmr chemical shifts and infrared spectra of phosphate diesters
Author(s) -
Lerner D. B.,
Becktel W. J.,
Everett R.,
Goodman M.,
Kearns D. R.
Publication year - 1984
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360231105
Subject(s) - chemistry , chemical shift , solvent , solvation , steric effects , solvent effects , infrared spectroscopy , nmr spectra database , phosphate , trimethyl phosphate , hydrogen bond , nuclear magnetic resonance spectroscopy , photochemistry , spectral line , organic chemistry , molecule , physics , astronomy
The effects of organic solvents on the 31 P‐mr chemical shifts of various phosphate diesters have been investigated in water and mixed‐organic solvent systems. The addition of organic solvents to cyclic phosphates and to diethyl phosphate causes large upfield shifts of the phosphorus resonance which are attributed to solvent‐induced changes in the local hydration of the phosphodiester group. This is consistent with the fact that there is an inverse correlation between the hydrogen‐bond‐donating ability of the solvents and the magnitude of the shifts they induce. Other possible interpretations, such as solvent‐induced ion pairing and solvent‐induced conformational changes, appear to be eliminated. Fourier‐transform ir study of the cyclic nucletides reveals that there are also large solvent‐induced shifts in the frequency of the antisymmetric OPO stretching frequency, and a comparison of the two types of measurements indicates that there is a linear correlation between shifts observed in the ir and in the 31 P‐nmr spectra. With UpU, the solvent‐induced 31 P‐nmr shifts are ∼3 times smaller than those observed with the cyclic phosphates and the solvent‐induced shift of the OPO band is reduced (factor of ∼1.7) as compared with the cyclic phosphates. With the single‐stranded polynuclotides, poly(C) and poly(U), the solvent‐induced shifts in both the nmr and ir are quite small (∼0.1 ppm and ∼1 cm −1 ). The very small solvent effects observed with poly(U) and poly(C) are attributed to a combination of steric effects and a polyelectrolyte effect which maintains a high density of counterions with waters of hydration in the vicinity of the charged backbone and makes the phosphates much less susceptible to solvent‐induced changes in hydration.