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72 RADIOCHEMISTRY, STABLE ISOTOPES, NUCLEAR ANALYTICAL METHODS, GENERAL CHEMISTRY last years [1]. These thermodynamically stable and kinetically inert 99m Tc chelates are good candidates for radiopharmaceuticals or their precursors. Due to the softness (HSAB) of the technetium(I) centre, chelators with soft donor atoms are preferred as the ligands. Widely studied in this respect are bi- and tridentate derivatives of pyridine and/or imidazole (aromatic N donors) in combination with other donor atoms, in particular sulphur. The aim of the present work is to select ligands that form very stable tricarbonyl complexes of technetium(I), and after further functionalization can be precursors for radiopharmaceuticals of the second generation. Two kinds of [Tc(CO) 3 LB] complexes were obtained and studied, where L is a neutral chelating ligand with either N,S donor atoms, N-methyl-2-pyridinecarbothioamide, L NS , or its analog with N,O donor atoms, N-methyl-2-pyridinecarboamide, L NO , while B is a monovalent anion or H 2 O. The complexes were prepared both with 99m Tc at n.c.a. level (B=OH – or H 2 O) and with 99 Tc in mg quantities (B=Cl – ). The 99m Tc complexes were investigated by HPLC and those of 99 Tc – by IR measurements. Na[ 99m TcO 4 ] was eluted from a 99 Mo/ 99m Tc generator using 0.9% saline. Synthesis of precursor 1 in water was carried out according to Alberto’s low-pressure method [2,3] and/or by using potassium boranocarbonate [4]. The complexes in n.c.a concentrations were obtained from 1 by adding a methanol solution of L to the precursor solution in a phosphate-buffered saline (PBS) to reach [L]=10 –3 M, followed by heating the mixture at 37 or 75 o C for 10-60 min. The complexes of 99 Tc were prepared in water-methanol solution by adding little excess of the ligand to the precursor solution and heating the mixture at 50 o C, then recrystallized from a mixture of dichloromethane-hexane. The IR spectra were carried out in KBr pellets using a Perkin Elmer 16 PC FT-IR spectrophotometer. Fig.1. IR spectrum of [Tc(CO) 3 L NS Cl]; L NS =N-methyl-2-pyridinecarbothioamide. We expect that each ligand coordinates the metal center bidently via the pyridine nitrogen and the X atom (X=O or S), forming a five-membered Fig.2. IR spectrum of [Tc(CO) 3 L NO Cl] (contaminated with some L NO ); L NO =N-methyl-2-pyridinecarboamide. chelate ring. This conclusion is supported by the similarity of IR spectra of the 99 Tc complexes studied (Figs.1 and 2) to those of their rhenium analogs [5,6]. Two characteristic peaks of CO vibrations (2026 and 1928 cm –1 ) confirm the existence of the 99 Tc(CO) 3 core in the complexes studied. The yield of the [ 99m Tc(CO) 3 L NX B] complexes (B=H 2 O and/or OH – ) was studied by HPLC [7]. After 40 min incubation at 75 o C, the [ 99m Tc(CO) 3 L NS B] complex was obtained with the nearly 100% yield (Fig.3), while the yield of [ 99m Tc(CO) 3 L NO B] was lower (53 to 84% depending on pH of the complex formation, Fig.4). Two forms of the complexes were observed: cationic (B=H 2 O), eluted as the peak No.2 on the chromatograms (Figs.3 and 4), and neutral (B=OH – ), eluted as the peak No.3. The equilibrium between these two forms depended on the complex and on pH of the complex formation. It was shifted to over 90% of the neutral form at pH>7 for [ 99m Tc(CO) 3 L NS B] (Fig.3), but for [ 99m Tc(CO) 3 L NO B] the cationic form predominated (from 50% at pH 3 to 64% at pH 10 (Fig.4). The coexistence of the two forms of the complexes, cationic and neutral, was also confirmed by paper electrophoresis. Under the appropriate experimental conditions (e.g. proper pH) two 99m Tc peaks appeared on the electropherograms: that remaining at the starting point corresponded to the neutral form, while that moving to the cathode corresponded to the cationic form. The easier hydrolysis of the [ 99m Tc(CO) 3 L NS H 2 O] + complex can hardly be discussed in terms of easier deprotonation of the H 2 O molecule coordinated to the technetium atom more strongly than in the analogous [ 99m Tc(CO) 3 L NO H 2 O] + complex. The stronger coordination of the L NS than L NO ligand reflected by the greater yield (and stability) of the former complex, and the smaller positive charge on the technetium atom calculated for the former (0.14 e) than for the latter (0.31 e) [8] lead to the conclusion on the weaker bonding of the H 2 O molecule in the former species. Therefore, the hydrolysis proceeds most probably via the ligand exchange, i.e. the exchange of the coordinated H 2 O molecule for an OH – ion from the aqueous solution.
RADIOCHEMISTRY, STABLE ISOTOPES, NUCLEAR ANALYTICAL METHODS, GENERAL CHEMISTRY 73 Fig.3. HPLC chromatograms of the [ 99m Tc(CO) 3 L NS B] complexes obtained at different pH: (a) pH 3, (b) pH 7 and (c) pH 10. Peak 2 – [ 99m Tc(CO) 3 L NS (H 2 O)] + , peak 3 – [ 99m Tc(CO) 3 L NS (OH)]. The work was supported by the State Committee for Scientific Research (KBN) – grant No. 4 TO9A 11023. Part of the work ( 99 Tc complexes), carried out during the stay of Monika Łyczko at Paul Scherrer Institute (Switzerland), was financed from the European Commission under Marie Curie Actions for the Transfer of Knowledge – contract No. MTKD-CT-2004-509224. Fig.4. HPLC chromatograms of the [ 99m Tc(CO) 3 L NO B] complexes obtained at different pH: (a) pH 3, (b) pH 7 and (c) pH 10. Peak 1 – precursor 1, peak 2 – [ 99m Tc(CO) 3 L NO (H 2 O)] + , peak 3 – [ 99m Tc(CO) 3 L NO (OH)]. References [1]. Mundwiler S., Kündig M., Ortner K., Alberto R.: Dalton Trans., 1320-1328 (2004). [2]. Alberto R., Schibli R., Angst D., Schubiger A.P., Abram U., Abram S., Kaden T.A.: Transition Met. Chem., 22, 597-601 (1997). [3]. Alberto R., Schibli R., Waibel R., Abram U., Schubiger A.P.: Coord. Chem. Rev., 190-192, 901-919 (1999). [4]. Alberto R., Ortner K., Wheatley N., Schibli R., Schubiger A.P.: J. Am. Chem. Soc., 123, 3135-3136 (2001).
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ANNUAL REPORT 2005 50 years in the
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CONTENTS GENERAL INFORMATION 9 MANA
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DETERMINATION OF CADMIUM, LEAD, COP
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NUCLEONIC CONTROL SYSTEMS AND ACCEL
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GENERAL INFORMATION 9 GENERAL INFOR
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MANAGEMENT OF THE INSTITUTE 11 MANA
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MANAGEMENT OF THE INSTITUTE 13 •
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SCIENTIFIC STAFF 15 5. Danilczuk Ma
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NUKLEONIKA 169 NUKLEONIKA THE INTER
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NUKLEONIKA 171 7. Influence of time
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INTERVIEWS IN 2005 173 INTERVIEWS I
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EDUCATION 209 EDUCATION Ph.D. PROGR
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RESEARCH PROJECTS AND CONTRACTS 211
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LECTURES AND SEMINARS DELIVERED OUT
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AWARDS IN 2005 221 AWARDS IN 2005 1
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INDEX OF THE AUTHORS 235 Lisowska H
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