Geometry dependence of spin-spin couplings in cyanamide by DFT analysis

Tanja Van Mourik, Andrew J. Dingley

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)

Abstract

There have been numerous theoretical and experimental investigations examining NMR parameters related to non-amino N-H center dot center dot center dot N H-bonded moieties in both biological and chemical contexts. In contrast, little information on the geometry dependence of NMR parameters related to the biologically important H-bond donor amino group is available. Herein, the geometric dependencies of the one-bond amino N-H spin-spin coupling constants [(1)J(NH)] in the cyanamide monomer and dimer have been computed with B3LYP and the aug-c-pVTZ-su0 basis set. In an isolated planar cyanamide molecule, the vertical bar(1)J(NH)vertical bar couplings were found to increase as the N-H bond lengthened. In contrast, in the planar cyanamide dimer the size of the H-bonded amino N-H coupling {vertical bar 1J(NdHfree)vertical bar coupling for NdHd distances up to 1.18 angstrom (for a fixed NdHfree distances of 1.006 angstrom). Hence, the decrease of vertical bar(1)J(NH)vertical bar with increasing N-H distance, as well as the larger value of vertical bar 1J(NdHfree), were only observed for situations where the amino group is involved in an H-bonding interaction. This is attributed to electron redistribution induced by the presence of the second cyanamide molecule. Similar electron-redistribution effects are thought to be responsible for the observed distance dependence of computed (1)J(NH) coulings of H-bonded amino groups in near-planar G-quarter structures. Here, the vertical bar(1)J(NH)vertical bar couplings of the amino N-H bonds decreased with increasing N-H bond length whereas the vertical bar(1)J(NdHd)vertical bar couplings are approximately 7 Hz larger than the vertical bar 1J(NdHfree)vertical bar couplings despite the longer Nd-Hd bond length.

Original languageEnglish
Pages (from-to)288-296
Number of pages9
JournalChemPhysChem
Volume8
DOIs
Publication statusPublished - 2 Feb 2007

Keywords

  • cyanamide
  • density functional calculations
  • guanine quartets
  • hydrogen bonds
  • NMR spectroscopy
  • DENSITY-FUNCTIONAL THEORY
  • CORRELATED MOLECULAR CALCULATIONS
  • HYDROGEN-BONDING REGIONS
  • CONSISTENT BASIS-SETS
  • GAUSSIAN-BASIS SETS
  • AB-INITIO
  • SCALAR COUPLINGS
  • SHIELDING CONSTANTS
  • WAVE-FUNCTIONS
  • SEXTUPLE ZETA

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