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On hydroxyapatite
Archs oral Biol. Vol.12. pp.165-166,
1967. Pergamon Press Ltd. Printed in Gt. Britain.
SHORT COMMUNI CATIONS ON HYDROXYAPATITE
v.
M. EhmNAGAR*
Infrared Institute, Fisk University, Nashville, Tennessee, U.S.A. IN CONNECTION with the interesting contribution of FOWLER,MORENOand BROWN (1966) on the infrared spectra hydroxyapatite and octacalcium phosphate, we should like to report some observations on hydroxyapatite. We are investigating the infrared spectra of hydroxyapatite, chlorapatite, fluorapatite, etc. in the light of detailed knowledge of atomic positions provided by X-ray studies. The three apatites are structurally very similar; however, the symmetric stretching motion varies slightly among the three apatitic systems. The very slight shift in frequencies can be correlated with local structural differences in the vicinity of the P0,3- ion (STUTMAN,TERMINEand POSNER,1965). In the region 500-400 cm-‘, FOWLERand coworkers (1966) observed a weak band at 472 cm-l. Usually, two bands appear consistently in the spectrum of hydroxyapatite which absorb at 425 and 472 cm-l. Fowler, MORENOand BROWN (1966) thus failed to observe the other absorption at 425 cm-l. These two very weak bands are generally less intense than the other three members 578, 605 and 630 cm-’ of vibration v,. They are assigned as the difference tones as the numerical values of their frequencies are close in magnitude to the difference between v3 and vp (for example: V, -v4, 1083 - 605 = 478 and 1045 - 605 = 440 cm-l). STUTMANand collaborators (1965) also observed only one band in the 470-480 cm-l region and excluded it from a v, designation. FOWLERet al. (1966) referred to the weak band at 472 cm-’ as too far removed from 350 cm-l to be a component of v2. The band at 425 cm-’ is nearer to 350 cm-l to be a component of va. However, we have assigned it to a difference tone as explained above. The lowering of the symmetry of the phosphate ion from Td to C, causes v1 at 980 cm-l to become infrared active. The normal mode v2 at 363 cm-l should also thus become infra-red active. Two bands are observed for hydroxyapatite near 350 and 260 cm-l. It is, however, not possible to interpret the doubly degenerate mode v2 at this stage. But two definite bands are observed in the region 370-250 cm-l. We have not observed the four new bands 1985, 2050, 2075 and 2140 cm-’ in hydroxyapatite as reported by FOWLERet al. (1966). The hydroxyapatite peak at 630 cm-l, due to the phosphate ions, is absent in chlorapatite, fluorapatite and in mixed apatites. $ Present address: Department of Chemistry,Kentucky State College, Frankfort, Kentucky, U.S.A. 165
166
V. M. BHATNAGAR
Acknowledgement-This investigation was supported by research grant DE-02105 02 to the Infrared Spectroscopy Institute from the Department of Health, Education and Welfare. I thank Prof. NELSONFUSON, Director, Fisk Infrared Spectroscopy Institute for his interest and useful discussions. REFERENCES FOWLER, B. O., MORENO,E. C. and BROWN,W. E. 1966. Infra-red spectra of hydroxyapatite, octacalcium phosphate and pyrolysed octacalcium phosphate. Archs oral Biol. 11,477492. STUTMAN, J. M., TBRMINE, J. D. and POSNER,A. S. 1965. Vibrational spectra and structure of the phosphate ion in come calcium phosphates. Trans. N. Y. Acad. Sci. 27, 669-675.
1967. Pergamon Press Ltd. Printed in Gt. Britain.
SHORT COMMUNI CATIONS ON HYDROXYAPATITE
v.
M. EhmNAGAR*
Infrared Institute, Fisk University, Nashville, Tennessee, U.S.A. IN CONNECTION with the interesting contribution of FOWLER,MORENOand BROWN (1966) on the infrared spectra hydroxyapatite and octacalcium phosphate, we should like to report some observations on hydroxyapatite. We are investigating the infrared spectra of hydroxyapatite, chlorapatite, fluorapatite, etc. in the light of detailed knowledge of atomic positions provided by X-ray studies. The three apatites are structurally very similar; however, the symmetric stretching motion varies slightly among the three apatitic systems. The very slight shift in frequencies can be correlated with local structural differences in the vicinity of the P0,3- ion (STUTMAN,TERMINEand POSNER,1965). In the region 500-400 cm-‘, FOWLERand coworkers (1966) observed a weak band at 472 cm-l. Usually, two bands appear consistently in the spectrum of hydroxyapatite which absorb at 425 and 472 cm-l. Fowler, MORENOand BROWN (1966) thus failed to observe the other absorption at 425 cm-l. These two very weak bands are generally less intense than the other three members 578, 605 and 630 cm-’ of vibration v,. They are assigned as the difference tones as the numerical values of their frequencies are close in magnitude to the difference between v3 and vp (for example: V, -v4, 1083 - 605 = 478 and 1045 - 605 = 440 cm-l). STUTMANand collaborators (1965) also observed only one band in the 470-480 cm-l region and excluded it from a v, designation. FOWLERet al. (1966) referred to the weak band at 472 cm-’ as too far removed from 350 cm-l to be a component of v2. The band at 425 cm-’ is nearer to 350 cm-l to be a component of va. However, we have assigned it to a difference tone as explained above. The lowering of the symmetry of the phosphate ion from Td to C, causes v1 at 980 cm-l to become infrared active. The normal mode v2 at 363 cm-l should also thus become infra-red active. Two bands are observed for hydroxyapatite near 350 and 260 cm-l. It is, however, not possible to interpret the doubly degenerate mode v2 at this stage. But two definite bands are observed in the region 370-250 cm-l. We have not observed the four new bands 1985, 2050, 2075 and 2140 cm-’ in hydroxyapatite as reported by FOWLERet al. (1966). The hydroxyapatite peak at 630 cm-l, due to the phosphate ions, is absent in chlorapatite, fluorapatite and in mixed apatites. $ Present address: Department of Chemistry,Kentucky State College, Frankfort, Kentucky, U.S.A. 165
166
V. M. BHATNAGAR
Acknowledgement-This investigation was supported by research grant DE-02105 02 to the Infrared Spectroscopy Institute from the Department of Health, Education and Welfare. I thank Prof. NELSONFUSON, Director, Fisk Infrared Spectroscopy Institute for his interest and useful discussions. REFERENCES FOWLER, B. O., MORENO,E. C. and BROWN,W. E. 1966. Infra-red spectra of hydroxyapatite, octacalcium phosphate and pyrolysed octacalcium phosphate. Archs oral Biol. 11,477492. STUTMAN, J. M., TBRMINE, J. D. and POSNER,A. S. 1965. Vibrational spectra and structure of the phosphate ion in come calcium phosphates. Trans. N. Y. Acad. Sci. 27, 669-675.