Determination of molecular binding in aqueous solution from optical activity measurements. Interaction of tryptophan with alkylxanthines
✍ Scribed by Masahiro Nakano; Takeru Higuchi
- Publisher
- John Wiley and Sons
- Year
- 1968
- Tongue
- English
- Weight
- 336 KB
- Volume
- 57
- Category
- Article
- ISSN
- 0022-3549
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✦ Synopsis
Although the feasibility of using ORD for determining stability constants of molecular complexes in organic solvent has already been shown, the present investigation appears to be the first attempt to apply it to an aqueous system. Measurements at 3 30 mp show distinct changes in the apparent optical activity of the zwitter ionic form of the amino acid when alkylxanthines were added to its solutions. These readings when analyzed by the iterative procedure previously developed for PMR data have yielded self-consistent stability constant values. Results are given for interaction with cdeine, theophylline, 8-methoxycaffeine, 1,3-dimethyluracil, and sarcosine anhydride. From measurements at several temperatures the heat of binding of tryptophan with caffeine was shown to be -4.0 kcal./mole and that with theophylline to be -4.2 kcal./mole. These results appear to be consistent with results obtained previously on related systems.
LTHOUGH IT HAS BEEN demonstrated that
A optical activity measurements can be effectively used to determine stability constants of bound species in essentially nonpolar solvents (l), no attempt appears to have been made to utilize these readings for estimating binding tendencies in aqueous solutions. In nonpolar solutions the binding behaviors arise primarily through hydrogen bonding of the interactants.