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Two‐dimensional vibrational correlation spectroscopy of in vitro hydroxyapatite maturation

Two‐dimensional vibrational correlation spectroscopy of in vitro hydroxyapatite maturation Two‐dimensional (2‐D) Raman and 2‐D IR correlation spectroscopy are applied to analyze changes in the ν4 region of the IR spectrum and in the ν1 region of the Raman spectrum during the maturation of hydroxyapatite (HA) following the solution‐mediated conversion of amorphous calcium phosphate (ACP) to HA. The ν1 region of the Raman spectrum exhibits a frequency shift and sharpening during the maturation. Comparison of the experimental and simulated 2‐D plots for this process suggests that the shift of a single peak, rather than a change in the relative intensity of two overlapped bands, is responsible for the observed spectral changes. The ν4 mode of the PO3−4 ion (T2 symmetry in the free species) splits into a triplet with components near 563, 575, and 603 cm−1 in HA. In addition, broad features appear at 540 and 617 cm−1. During the latest stages of the maturation, an OH− librational mode develops at ∼632 cm−1. Changes in the relative intensities of three components of the ν4 mode are not all correlated with each other. The synchronous 2‐D plots reveal that the 563 and 603 cm−1 pair are positively correlated while the feature at 575 cm−1 is absent. A 587 cm−1 mode arising from ACP is negatively correlated with the 563 and 603 cm−1 pair and is both synchronously (positively) and asynchronously correlated with the 540 cm−1 feature during the early stages of the maturation but is absent from 2‐D plots of the later stages of the maturation. Cross correlations between the ν4 mode and the ν1,ν3 contour generally confirm and extend previous assignments for the latter spectral region. Finally, the suitability of the 2‐D approach for analysis of IR spectral images is examined through studies of HA crystallinity in a human iliac crest biopsy sample. Trabecular bone contains a fraction of HA that is more crystalline and mature than could be achieved in vitro during the room temperature ACP → HA interconversion. © 2000 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 57: 129–139, 2000 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Biopolymers Wiley

Two‐dimensional vibrational correlation spectroscopy of in vitro hydroxyapatite maturation

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Publisher
Wiley
Copyright
Copyright © 2000 John Wiley & Sons, Inc.
ISSN
0006-3525
eISSN
1097-0282
DOI
10.1002/(SICI)1097-0282(2000)57:3<129::AID-BIP1>3.3.CO;2-F
Publisher site
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Abstract

Two‐dimensional (2‐D) Raman and 2‐D IR correlation spectroscopy are applied to analyze changes in the ν4 region of the IR spectrum and in the ν1 region of the Raman spectrum during the maturation of hydroxyapatite (HA) following the solution‐mediated conversion of amorphous calcium phosphate (ACP) to HA. The ν1 region of the Raman spectrum exhibits a frequency shift and sharpening during the maturation. Comparison of the experimental and simulated 2‐D plots for this process suggests that the shift of a single peak, rather than a change in the relative intensity of two overlapped bands, is responsible for the observed spectral changes. The ν4 mode of the PO3−4 ion (T2 symmetry in the free species) splits into a triplet with components near 563, 575, and 603 cm−1 in HA. In addition, broad features appear at 540 and 617 cm−1. During the latest stages of the maturation, an OH− librational mode develops at ∼632 cm−1. Changes in the relative intensities of three components of the ν4 mode are not all correlated with each other. The synchronous 2‐D plots reveal that the 563 and 603 cm−1 pair are positively correlated while the feature at 575 cm−1 is absent. A 587 cm−1 mode arising from ACP is negatively correlated with the 563 and 603 cm−1 pair and is both synchronously (positively) and asynchronously correlated with the 540 cm−1 feature during the early stages of the maturation but is absent from 2‐D plots of the later stages of the maturation. Cross correlations between the ν4 mode and the ν1,ν3 contour generally confirm and extend previous assignments for the latter spectral region. Finally, the suitability of the 2‐D approach for analysis of IR spectral images is examined through studies of HA crystallinity in a human iliac crest biopsy sample. Trabecular bone contains a fraction of HA that is more crystalline and mature than could be achieved in vitro during the room temperature ACP → HA interconversion. © 2000 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 57: 129–139, 2000

Journal

Biopolymers – Wiley

Published: Jan 1, 2000

Keywords: 2‐D correlation spectroscopy; Raman spectroscopy; IR spectroscopy; in vitro ; hydroxyapatite; maturation

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