title: Distance measurements between boron and carbon at natural abundance using magic angle spinning REAPDOR NMR and a universal curve.
abstract: The rotational echo adiabatic passage double resonance (REAPDOR) magic angle spinning NMR experiment efficiently recouples the dipolar interaction between a spin-1/2 and a spin >1/2, enabling accurate and efficient measurement of their inter-nuclear distance. We demonstrate that under adiabatic conditions a universal curve that depends only on the inter-nuclear distance fits the REAPDOR recoupling curve for a (13)C (spin-1/2)-(11)B (spin-3/2) spin pair. In 4-(hydroxymethyl)phenylboronic acid MIDA ester the inter-nuclear distance between the methyl carbon and boron was determined to be 2.76 ± 0.14 Å, in agreement with the distance of 2.68 Å determined by X-ray crystallography. Similar experiments performed at two different spinning speeds and fit simultaneously to the same curve give a distance of 2.73 Å and distances to other carbons in the molecule are also determined. The low abundance of carbon-13 at natural abundance (1.1%) and the reduced abundance of boron-11 (80.1%) render the experiment insensitive to (13)C-(13)C homonuclear couplings and significantly reduce the effect of a second boron nucleus at a longer distance. This approach can be extended to any spin-3/2 coupled to a spin-1/2.
authors.affiliation: School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, 69978, Tel Aviv, Israel.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Nimerovsky
authors.forename: Amir
authors.initials: A
authors.lastname: Goldbourt
mesh_terms: D001895:Boron / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D002247:Carbon Isotopes / Q000737:chemistry; D018360:Crystallography, X-Ray; D004952:Esters; D007098:Imino Acids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy
chemical_list: D002247:Carbon Isotopes; D004952:Esters; D007098:Imino Acids; C533766:N-methyliminodiacetic acid; D002244:Carbon; D001895:Boron