Two-dimensional vibrational correlation spectroscopy of in vitro hydroxyapatite maturation

✍ Scribed by H. Ou-Yang; E. P. Paschalis; A. L. Boskey; R. Mendelsohn

• Publisher: Wiley (John Wiley & Sons)
• Year: 2000
• Tongue: English
• Weight: 313 KB
• Volume: 57
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/(sici)1097-0282(2000)57:3<129::aid-bip1>3.0.co;2-o

✦ Synopsis

Two-dimensional (2-D)

Raman and 2-D IR correlation spectroscopy are applied to analyze changes in the 4 region of the IR spectrum and in the 1 region of the Raman spectrum during the maturation of hydroxyapatite (HA) following the solution-mediated conversion of amorphous calcium phosphate (ACP) to HA. The 1 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 4 mode of the PO 4 3Ϫ ion (T 2 symmetry in the free species) splits into a triplet with components near 563, 575, and 603 cm Ϫ1 in HA. In addition, broad features appear at 540 and 617 cm Ϫ1 . During the latest stages of the maturation, an OH Ϫ librational mode develops at ϳ632 cm Ϫ1 . Changes in the relative intensities of three components of the 4 mode are not all correlated with each other. The synchronous 2-D plots reveal that the 563 and 603 cm Ϫ1 pair are positively correlated while the feature at 575 cm Ϫ1 is absent. A 587 cm Ϫ1 mode arising from ACP is negatively correlated with the 563 and 603 cm Ϫ1 pair and is both synchronously (positively) and asynchronously correlated with the 540 cm Ϫ1 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 4 mode and the 1 , 3 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 3 HA interconversion.