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Raman spectroscopic evidence for Tc-Oxo cores in Tc-HEDP complexes
Appl. Radiat. ht. Vol. 38, No. I, pp. 569-570. Inl. J. Radiat. Appl. Instrum. Part A Printed in Great Britain. All rights reserved
1987 Copyright
0
0883-2889/87 $3.00 + 0.00 1987 Pergamon Journals Ltd
Raman Spectroscopic Evidence for Tc-0x0 Cores in Tc-HEDP Complexes M. V. MIKELSONS Department
of Chemistry.
Purdue
and
T. C. PINKERTON*
University,
Introduction Technetium diphosphonate complexes are widely used as diagnostic bone imaging agents in nuclear medicine.“) Yet despite widespread use of these species, their structures are unknown and the factors that govern their biodistributions are not fully understood. One of the many complicating factors inhibiting the elucidation of the nature of these complexes is the fact that clinically used imaging agents exist as complex mixtures of Tc-tiiphosphonate species. Technetium hydroxyethylidene diphosphonate (Tc-HEDP) mixtures have been shown to consist of more than 13 technetium containing complexes.(2s3) Consequently, characterization of Tc-HEDP complexes requires their isolation from such mixtures prior to analysis. Partial characterization of separated Tc-HEDP complexes has been achieved. Van den Brandc4) has suggested possible structures for Tc-HEDP(Sn) complexes based on triple isotope labeling, Wilson and Pinkerton”) determined the charges and partial molar volumes of selected components of a Tc-HEDP (NaBH,) mixture, and Desilets and Pinkerton”) determined the approximate molecular weights for these same species based on high performance size exclusion chromatography. All of the proposed formulas for the Tc-HEDP complexes include Tc-0x0 cores. Such cores have been determined for other technetium complexes,@) but have not been directly determined for Tc-HEDP complexes. Technetium-oxo cores can readily be identified by their vibrational energies. Characteristic absorption bands for Tc=O (91&1020cm~‘) and O=Tc=O @O&850 cm-‘) have been determined using infrared spectroscopy. (7.8)The Tc-HEDP complexes, however, are not amenable to analysis by i.r. because of their aqueous matrix. An alternative to i.r. spectroscopy, which provides similar information, is Raman spectroscopy. Raman is ideal for the analysis of aqueous inorganic and organometallic complexes because water is a poor Raman scatterer, thus the matrix will not obscure the spectrum. Also, low energy vibra-
West Lafayette,
IN 47907,
U.S.A.
tions that are difficult to observe in the i.r. spectrum are easily detected in the Raman spectrum.(9~‘0) This communication describes the verification of the presence of Tc-0x0 cores in Tc-HEDP complexes by Raman spectroscopy. The Raman spectrum of a Tc-HEDP(NaBH,) mixture is presented and attempts to acquire the Raman spectra of isolated Tc-HEDP components are described. The results verify the presence of Tc-0x0 cores in Tc-HEDP complexes.
Experimental The Tc-HEDP(NaBH,) complexes were prepared aerobically by the reduction of 99Tc0; with NaBH, in the presence of excess HEDP, as described elsewhere.(*) Technetium was obtained from Oak Ridge National Laboratories (Oak Ridge, Tenn., 99% pure) as NH, 99Tc0,. This material was converted to KTcO, by metathesis with KOH and recrystallized twice prior to its use. Sodium brohydride was obtained from Alfa Products, and the HEDP was from Procter and Gamble as the disodium salt. Separation of the Tc-HEDP complexes was achieved by anionexchange HPLC using a 0.85 M sodium acetate mobile phase. This separation has been described in detail elsewhere.(2) The individual Tc-HEDP complexes were isolated by collecting the chromatographically separated components. The Raman spectra were obtained using a computer controlled laser-Raman spectrometer. A Data General Nova 2/10 minicomputer was used for control of the spectrometer and for post-run datamanipulation. A Spex Model 1400 double monochromater was connected to the computer via a general purpose digital interface. A Coherent Radiation tunable argon ion laser, operated at 514.5 nm and 3000 mW incident power, served as the excitation source. The design and construction of this instrument has been discussed elsewhere.(“)
Results and Discussion * Corresponding Company, MI 49001,
Control U.S.A.
author: current address-The Upjohn Division, Bldg. 259-12, Kalamazoo,
A Tc-HEDP(NaBH,) technetate, was prepared 569
mixture, 5 mM in perand several components
M. V. MIKEL~ONS and T. C. PINKERTON
570
were separated and collected. The Raman spectrum of the mixture was acquired and attempts were made to obtain spectra of the isolated components. The spectrum of the Tc-HEDP(NaBH,) mixture is illustrated in Fig. 1A. Spectra of the isolated components could not be distinguished from that of the sodium acetate mobile phase. The concentrations of the isolated Tc-HEDP complexes were estimated to be approximately 0.005 mM, based on chromatographic dilution and the percentage of each component in the mixture. It is not surprising that scattering of these complexes could not be discerned in the presence of 0.85 M sodium acetate chromatographic mobile phase. The spectrum of the Tc-HEDP(NaBH,) mixture did show several strong scattering peaks. Since the solution contained 0.3 M Na,HEDP, it was important to determine which peaks were due to the HEDP. The Raman spectrum of 0.4 M Na,HEDP was aquired in order to assign the HEDP peaks in the Tc-HEDP mixture spectrum. The spectrum of HEDP is shown in Fig. 1B. After assigning the HEDP peaks and the water peak at 1643 cm-‘, the major unassigned peaks were at 970, 904, and 878 cm-‘. These frequencies correspond to Raman and i.r. stretching energies observed for Tc-0x0 cores.“* “I To verify this assignment, spectra of several species containing Tc-0x0 cores were obtained. The Raman spectrum of aqueous potassium pertechnetate contained a primary scattering peak at 906 cm- ‘, ammonium pertechnetate had a peak at 913 cm-‘, and TcO, was found to have a peak at 877 cm ‘. The pertechnetate peaks fit into the range of i.r. frequencies published by Baluka et ~1.“’ and the scatter-
ing frequency observed for trans TcO, agrees with i.r. absorptions reported by Vanderheyden et al.“@ Tc=O has been reported to have i.r. absorptions energies of between 910 and 1020cm-‘.(“) From these standards and literature values, the Tc-HEDP peak at 970 cm-’ is assigned to Tc=O, the 878 cm-’ peak is assigned to O=Tc=O, and the peak at 904cm-’ corresponds to the TcO; structure. Despite the inability to obtain Raman spectra of the isolated Tc-HEDP complexes, the spectrum of the mixture clearly indicates the presence of Tc-0x0 cores in at least some of the complexes. This corroborates the conclusions drawn from earlier investigations (21,5) ‘~ that these species include Tc-0x0 cores. This study was undertaken using only non-resonance Raman. Many of the Tc-HEDP complexes have electronic transitions in the visible range,(3) thus resonance Raman could be used to enhance the signal from the dilute isolated complexes. Further work in this area may allow the determination of the Raman spectra from individual TccHEDP complexes. Acknowledgements-The authors would like to thank Dr R. Dallinger for assistance in the acquisition of the Raman spectra. This investigation was supported in part by Public Health Service Grant RNM ROI-CA40110-1 awarded by the National Cancer Institute, Department of Health and Human Services.
References
5. 6. 7. 8. 9. 10. Il. 12. 13. 14. 15. 1600
1200
Frequency
Fig. 1
000
( cm-’
)
400
16.
17.
Eckelman W. C. and Levenson S. M. Int. J. Appl. Radial. Isot. 28, 67 (1977). Wilson G. M. and Pinkerton T. C. Anal. Chem. 57,246 (1985). Mikelsons M. V. and Pinkerton T. C. Anal. Chem. 58, 1007 (1986). Van den Brand J. A. G. M. Technetium (Tin) Ethane1-hyhdroxy-1-Diphosphonate Complexes: Preparation, Composition, and Biodistribution. ECN-98, Netherlands Energy Research Foundation, 1755 ZG Petten (NH), The Netherlands, October 1981. Desilets C. P. and Pinkerton T. C. A&. . . Radiaf. Isot. 38. 107 (1987). Davison A. and Jones A. G. Int. J. Appl. Radial. Isot. 33, 875 (1982). Baluka M., Hanuza J. and Jezowska-trzebiatowska B. Bull. Acad. Pol. Sci. 20, 271 (1972). Davison A., Jones A. G., Muller L., Tate R. and Trop S. Inorg. Chem. 20, 1160 (1981). Tobias R. S. J. Chem. Ed. 44, 2 (1967). Tobias R. S. J. Chem. Ed. 44, 70 (1967). Chrisman R. W., English J. C. and Tobias R. S. Appl. Spect. 30, 168 (1976). Spies H. and Johannsen B. Inorg. Chim. Acfa 48, 255 (1981). Davison A., Jones A. G. and Abrams M. J. Inorg. Chem. 20, 4300 (1981). Bandolini G., Nicolini M., Mazzi U. and Refosco F. J. Chem Sot. Dalfon Trans. 2505 (1984). Davison A., Jones A. G., Orvig C. and Sohn M. Inorg. Chem. 20, 1629 (1981). Vanderheyden J. L., Kettering A. R., Libson K.. Heeg M. J., Roecker L., Motz P., Whittle, R., Elder R. C. and Deutsch E. Inorn. Chem. 23. 3184 (1984). Deutsch E., Libson K. and Jurissbn S: Prog. Inorg. Chem. 30, 75 (1983).
1987 Copyright
0
0883-2889/87 $3.00 + 0.00 1987 Pergamon Journals Ltd
Raman Spectroscopic Evidence for Tc-0x0 Cores in Tc-HEDP Complexes M. V. MIKELSONS Department
of Chemistry.
Purdue
and
T. C. PINKERTON*
University,
Introduction Technetium diphosphonate complexes are widely used as diagnostic bone imaging agents in nuclear medicine.“) Yet despite widespread use of these species, their structures are unknown and the factors that govern their biodistributions are not fully understood. One of the many complicating factors inhibiting the elucidation of the nature of these complexes is the fact that clinically used imaging agents exist as complex mixtures of Tc-tiiphosphonate species. Technetium hydroxyethylidene diphosphonate (Tc-HEDP) mixtures have been shown to consist of more than 13 technetium containing complexes.(2s3) Consequently, characterization of Tc-HEDP complexes requires their isolation from such mixtures prior to analysis. Partial characterization of separated Tc-HEDP complexes has been achieved. Van den Brandc4) has suggested possible structures for Tc-HEDP(Sn) complexes based on triple isotope labeling, Wilson and Pinkerton”) determined the charges and partial molar volumes of selected components of a Tc-HEDP (NaBH,) mixture, and Desilets and Pinkerton”) determined the approximate molecular weights for these same species based on high performance size exclusion chromatography. All of the proposed formulas for the Tc-HEDP complexes include Tc-0x0 cores. Such cores have been determined for other technetium complexes,@) but have not been directly determined for Tc-HEDP complexes. Technetium-oxo cores can readily be identified by their vibrational energies. Characteristic absorption bands for Tc=O (91&1020cm~‘) and O=Tc=O @O&850 cm-‘) have been determined using infrared spectroscopy. (7.8)The Tc-HEDP complexes, however, are not amenable to analysis by i.r. because of their aqueous matrix. An alternative to i.r. spectroscopy, which provides similar information, is Raman spectroscopy. Raman is ideal for the analysis of aqueous inorganic and organometallic complexes because water is a poor Raman scatterer, thus the matrix will not obscure the spectrum. Also, low energy vibra-
West Lafayette,
IN 47907,
U.S.A.
tions that are difficult to observe in the i.r. spectrum are easily detected in the Raman spectrum.(9~‘0) This communication describes the verification of the presence of Tc-0x0 cores in Tc-HEDP complexes by Raman spectroscopy. The Raman spectrum of a Tc-HEDP(NaBH,) mixture is presented and attempts to acquire the Raman spectra of isolated Tc-HEDP components are described. The results verify the presence of Tc-0x0 cores in Tc-HEDP complexes.
Experimental The Tc-HEDP(NaBH,) complexes were prepared aerobically by the reduction of 99Tc0; with NaBH, in the presence of excess HEDP, as described elsewhere.(*) Technetium was obtained from Oak Ridge National Laboratories (Oak Ridge, Tenn., 99% pure) as NH, 99Tc0,. This material was converted to KTcO, by metathesis with KOH and recrystallized twice prior to its use. Sodium brohydride was obtained from Alfa Products, and the HEDP was from Procter and Gamble as the disodium salt. Separation of the Tc-HEDP complexes was achieved by anionexchange HPLC using a 0.85 M sodium acetate mobile phase. This separation has been described in detail elsewhere.(2) The individual Tc-HEDP complexes were isolated by collecting the chromatographically separated components. The Raman spectra were obtained using a computer controlled laser-Raman spectrometer. A Data General Nova 2/10 minicomputer was used for control of the spectrometer and for post-run datamanipulation. A Spex Model 1400 double monochromater was connected to the computer via a general purpose digital interface. A Coherent Radiation tunable argon ion laser, operated at 514.5 nm and 3000 mW incident power, served as the excitation source. The design and construction of this instrument has been discussed elsewhere.(“)
Results and Discussion * Corresponding Company, MI 49001,
Control U.S.A.
author: current address-The Upjohn Division, Bldg. 259-12, Kalamazoo,
A Tc-HEDP(NaBH,) technetate, was prepared 569
mixture, 5 mM in perand several components
M. V. MIKEL~ONS and T. C. PINKERTON
570
were separated and collected. The Raman spectrum of the mixture was acquired and attempts were made to obtain spectra of the isolated components. The spectrum of the Tc-HEDP(NaBH,) mixture is illustrated in Fig. 1A. Spectra of the isolated components could not be distinguished from that of the sodium acetate mobile phase. The concentrations of the isolated Tc-HEDP complexes were estimated to be approximately 0.005 mM, based on chromatographic dilution and the percentage of each component in the mixture. It is not surprising that scattering of these complexes could not be discerned in the presence of 0.85 M sodium acetate chromatographic mobile phase. The spectrum of the Tc-HEDP(NaBH,) mixture did show several strong scattering peaks. Since the solution contained 0.3 M Na,HEDP, it was important to determine which peaks were due to the HEDP. The Raman spectrum of 0.4 M Na,HEDP was aquired in order to assign the HEDP peaks in the Tc-HEDP mixture spectrum. The spectrum of HEDP is shown in Fig. 1B. After assigning the HEDP peaks and the water peak at 1643 cm-‘, the major unassigned peaks were at 970, 904, and 878 cm-‘. These frequencies correspond to Raman and i.r. stretching energies observed for Tc-0x0 cores.“* “I To verify this assignment, spectra of several species containing Tc-0x0 cores were obtained. The Raman spectrum of aqueous potassium pertechnetate contained a primary scattering peak at 906 cm- ‘, ammonium pertechnetate had a peak at 913 cm-‘, and TcO, was found to have a peak at 877 cm ‘. The pertechnetate peaks fit into the range of i.r. frequencies published by Baluka et ~1.“’ and the scatter-
ing frequency observed for trans TcO, agrees with i.r. absorptions reported by Vanderheyden et al.“@ Tc=O has been reported to have i.r. absorptions energies of between 910 and 1020cm-‘.(“) From these standards and literature values, the Tc-HEDP peak at 970 cm-’ is assigned to Tc=O, the 878 cm-’ peak is assigned to O=Tc=O, and the peak at 904cm-’ corresponds to the TcO; structure. Despite the inability to obtain Raman spectra of the isolated Tc-HEDP complexes, the spectrum of the mixture clearly indicates the presence of Tc-0x0 cores in at least some of the complexes. This corroborates the conclusions drawn from earlier investigations (21,5) ‘~ that these species include Tc-0x0 cores. This study was undertaken using only non-resonance Raman. Many of the Tc-HEDP complexes have electronic transitions in the visible range,(3) thus resonance Raman could be used to enhance the signal from the dilute isolated complexes. Further work in this area may allow the determination of the Raman spectra from individual TccHEDP complexes. Acknowledgements-The authors would like to thank Dr R. Dallinger for assistance in the acquisition of the Raman spectra. This investigation was supported in part by Public Health Service Grant RNM ROI-CA40110-1 awarded by the National Cancer Institute, Department of Health and Human Services.
References
5. 6. 7. 8. 9. 10. Il. 12. 13. 14. 15. 1600
1200
Frequency
Fig. 1
000
( cm-’
)
400
16.
17.
Eckelman W. C. and Levenson S. M. Int. J. Appl. Radial. Isot. 28, 67 (1977). Wilson G. M. and Pinkerton T. C. Anal. Chem. 57,246 (1985). Mikelsons M. V. and Pinkerton T. C. Anal. Chem. 58, 1007 (1986). Van den Brand J. A. G. M. Technetium (Tin) Ethane1-hyhdroxy-1-Diphosphonate Complexes: Preparation, Composition, and Biodistribution. ECN-98, Netherlands Energy Research Foundation, 1755 ZG Petten (NH), The Netherlands, October 1981. Desilets C. P. and Pinkerton T. C. A&. . . Radiaf. Isot. 38. 107 (1987). Davison A. and Jones A. G. Int. J. Appl. Radial. Isot. 33, 875 (1982). Baluka M., Hanuza J. and Jezowska-trzebiatowska B. Bull. Acad. Pol. Sci. 20, 271 (1972). Davison A., Jones A. G., Muller L., Tate R. and Trop S. Inorg. Chem. 20, 1160 (1981). Tobias R. S. J. Chem. Ed. 44, 2 (1967). Tobias R. S. J. Chem. Ed. 44, 70 (1967). Chrisman R. W., English J. C. and Tobias R. S. Appl. Spect. 30, 168 (1976). Spies H. and Johannsen B. Inorg. Chim. Acfa 48, 255 (1981). Davison A., Jones A. G. and Abrams M. J. Inorg. Chem. 20, 4300 (1981). Bandolini G., Nicolini M., Mazzi U. and Refosco F. J. Chem Sot. Dalfon Trans. 2505 (1984). Davison A., Jones A. G., Orvig C. and Sohn M. Inorg. Chem. 20, 1629 (1981). Vanderheyden J. L., Kettering A. R., Libson K.. Heeg M. J., Roecker L., Motz P., Whittle, R., Elder R. C. and Deutsch E. Inorn. Chem. 23. 3184 (1984). Deutsch E., Libson K. and Jurissbn S: Prog. Inorg. Chem. 30, 75 (1983).