A REDOR study of diammonium hydrogen phosphate: A model for distance measurements from adsorbed molecules to surfaces

Gil Goobes, Vinodhkumar Raghunathan, Elizabeth A. Louie, James M. Gibson, Gregory L. Olsen, Gary P. Drobny

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Magic angle spinning NMR techniques can be used to determine the molecular structure of proteins adsorbed onto polymer and mineral surfaces, but the degree to which the orientation of proteins on surfaces can be uniquely determined by NMR is less well understood. In this manuscript, REDOR data obtained from model systems are analyzed with a view to determine the orientation of rare spins coupled to a lattice populated by strongly coupled spin 12 nuclei. When the surface is populated by closely spaced spins, the REDOR dephasing of a rare spin on the protein contact point to the surface is under certain circumstances complicated by contributions from homonuclear dipolar interactions between the spins of the lattice. To study multiple spin effects on the dephasing signal in rotational-echo-double-resonance experiments, we carried out a measurement on crystalline diammonium hydrogen phosphate as a model for a spin system with multiple dipolar interactions. Information about the 31P-31P interactions is gathered from the reference measurement in the experiment. To fit the experimental 15N and 31P dephasing data well, it was necessary to account for as many as 6 and 8 spins in simulations, respectively. Using a single spin-pair interaction with an unknown distance yielded a good fit to the 31P data with a distance of 2.7 Å that is nearly an Angström shorter than the shortest distance in the crystal structure. Homonuclear couplings are shown to have a significant effect on the expected dephasing.

Original languageEnglish
Pages (from-to)242-250
Number of pages9
JournalSolid State Nuclear Magnetic Resonance
Issue number1-3
StatePublished - Feb 2006
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation (EEC-9529161 and DMR-0110505) and the National Dental Institute (DE-12554). J.M.G. is supported by a training grant from the National Institute of Dental and Craniofacial Research (DE-07023).


  • Biomineral
  • Diammonium hydrogen phosphate
  • Homonuclear couplings
  • Nitrogen
  • Phosphorous
  • Protein
  • Recoupling
  • Spin cluster
  • Surface


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