This study demonstrates the mutual orientation of three tensor interactions in a single NMR experiment. The orientation of the 15N chemical shift tensor relative to the molecular frame has thus been determined in polycrystalline L-[1-13C] alanyl-L-[15N] alanine. The 13C–15N and 15N–1H dipole interactions are determined using the 1H dipole-modulated, 13C dipole-coupled 15N spectrum obtained as a transform of the data in t2. From simulations of the experimental spectra, two sets of polar angles have been determined relating the 13C–15N and 15N–1H dipoles to the 15N chemical shift tensor. The values determined are βCN =106°, αCN =5° and βNH =−19°, αNH =12°. The experiment verifies, without reference to single crystal data, that σ33 lies in the peptide plane and σ22 is nearly perpendicular to the plane.
Molecular modeling of the large tributyl phosphate complex of europium provides a test of the sensitivity of
force field calculations to molecules within the interlayer of a trioctahedral smectite clay. A nonbonded
version of the consistent-valence force field was utilized. Parametrization is based on the structures of simple
clays and oxides. The simulations were carried out with complete translational freedom for all atoms. Energy
minimization of the hectorite supercell containing, within the interlayer, the Eu·3TBP complex as the trinitrate,
eight sodium cations, and 48 waters of hydration resulted in a d spacing of 18.66 Å. Molecular dynamics
simulations at 298 K resulted in a d spacing of 17.40 ± 0.15 Å. The experimental d spacing for hectorite
absorbed with the TBP solvate of Eu(NO3)3 is 17.18 ± 0.04 Å.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.