Kinetics of NMR cross-polarization from protons to phosphorus-31
in bone apatite and its mineral standards
Agnieszka Kaflak1, Anna Ślósarczyk2 and Waclaw Kolodziejski1
1
Medical University of Warsaw, Faculty of Pharmacy, Department of Inorganic and
Analytical Chemistry, ul. Banacha 1, 02-097 Warszawa, Poland.
2
AGH University of Science and Technology, Faculty of Materials Science and Ceramics, Al.
Mickiewicza 30, 30-059 Krakow, Poland.
Abstract
Human bone mineral, brushite (BRU) and synthetic apatites: hydroxyapatite hydrated
(HAh), hydroxyapatite calcined (HAc) and carbonatoapatite of type B with 9 wt% of CO32(CHA-B), were studied by variable-contact time experiments using conventional crosspolarization (CP) and CP preceded by additional proton spin lock. The CP kinetics, that is the
dependence of CP intensity on the contact time, was elucidated for the single 31P NMR peak
from those materials. Proton relaxation time in the rotating frame (T1ρH) was additionally
measured using a CP-based pulse sequence. In order to avoid an effect of magic angle
spinning (MAS) on CP and relaxation, all the experiments were carried out on static samples.
The CP kinetic functions for bone mineral and CHA-B were comprised of two
components corresponding to different kinetic models [1]. According to the classical model,
CP between the concerned spin systems is driven by the difference in their spin temperatures.
The non-classical model describes CP in heteronuclear spin clusters, which interact with bulk
protons by means of spin diffusion. The two CP components were deconvoluted and
characterised by appropriate kinetic parameters. The fast-relaxing component is from the
surface of apatite crystals and the slow-relaxing component is from the crystal interior. In the
former adsorbed water is involved, while in the latter participate structural hydroxyl groups of
apatite. The interpretation was supported by 2D HETCOR experiments. The CP kinetic
results for HA and brushite were described by single, non-classical component. It follows that
bone and CHA-B have very large crystal surface areas, so the related classical CP components
can be easily observed. No HPO42- ions were detected in the bone mineral. The study shows
the similarity between carbonatoapatite of type B and bone mineral as shown by their CP
behaviour [2 - 4].
References:
1. Kolodziejski W, Klinowski J “Kinetics of cross-polarization in solid-state NMR. A guide
for chemists” Chem Rev 102 (2002) 613-628
2. A. Kaflak-Hachulska, A. Samoson, W. Kołodziejski „1H MAS and 1H → 31P CP/MAS
NMR Study of Human Bone Mineral” Calcified Tissue International 73 (2003) 476-486
3. W. Kolodziejski “Solid-State NMR Studies of Bone” Topics in Current Chemistry 246
(2005) 235-270
4. A. Kaflak, D. Chmielewski, A. Górecki, A. Slosarczyk, W. Kołodziejski „Efficiency of the
1
H→ 31P cross-polarization in bone apatite and its mineral standards” Solid State Nuclear
Magnetic Resonance 29 (2006) 345-348