Tc Complexes Research Articles

Size fractionated complexation of Tc(IV) with soil humic acids at varying solution conditions

There are currently multiple U.S. Department of Energy sites with significant quantities of technetium-99 stored under a variety of conditions. While it is known that Tc in the VII oxidation state has a very high rate of envi- ronmental migration, little is known about the chemistry of the IV oxidation state, expected to occur under anoxic conditions. In this work, the binding of Tc(IV) with humic acid (HA) of varying sizes was studied using ultracentri- fugation and total organic carbon analysis. A constant ratio HA-bound Tc(IV):HA concentration was observed for the 10-1,000 nm HA size range and it is independent of pH, ionic strength, background electrolyte and HA origin. HA zeta potentials were determined; the largest HA size frac- tion had a considerably less negative zeta potential than the smaller size fractions; the zeta potential of the colloidal size fraction (10-1,000 nm) was independent of solution conditions. 13 C cross polarization magic angle spinning and attenuated total reflectance-Fourier transform infrared spectroscopy results indicate that solid filtrates of HA from two different origins have distinct spectra that were not altered with changes in solution conditions. This work shows that we are able to use zeta potential measurements to describe binding characteristics of HA with Tc(IV).

Nitrosyltechnetium complexes with (2-aminomethylphenyl)diphenylphosphine

Reactions of (NBu4)[Tc(NO)Cl4(MeOH)] (1) with (2-aminomethylphenyl)diphenylphosphine, H2L1, give different products depending on the conditions applied. An equimolare reaction in MeOH gives the technetium(II) monochelate [Tc(NO)Cl3(H2L1-κN,P)] (2) as the sole product, which could be isolated. Reduction of the metal ion and the formation of the Tc(I) complexes [Tc(NO)Cl2(H2L1-κN,P)(H2L1-κN)] (3) and [Tc(NO)Cl(H2L1-κN,P)2]Cl (4), besides some (NBu4)[Tc(NO)Cl4(H2L1-κN)] (5), is observed when an excess of the H2L1 is used in the same solvent. Reactions in acetonitrile are less defined and only the Tc(II) compound (NBu4)[Tc(NO)Cl4(H2L1O-κN)] (6) could be isolated from such reactions in crystalline form.The products were studied spectroscopically and by X-ray diffraction. The aminophosphine acts as monodentate nitrogen donor ligand or as N,P chelator.

Synthesis and evaluation of a new 99mTc(I)‐tricarbonyl complex bearing the 5‐nitroimidazol‐1‐yl moiety as potential hypoxia imaging agent

The objective of this work was to develop a novel (99m) Tc complex bearing the 5-nitroimidazol-1-yl moiety with recognised selectivity towards hypoxic tissue, as a potential radiopharmaceutical for imaging tumour hypoxia. The new metronidazole derivative (2-amine-3-[2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethylthio]propanoic acid) (L) containing adequate groups to coordinate technetium through the formation of a Tc(I)-tricarbonyl complex was synthesised with adequate yield (33%) and characterised by spectroscopy. Labelling was performed by substitution of three labile water molecules of the technetium tricarbonyl precursor, fac-[(99m)Tc(CO)3 (H2O)3](+) with the ligand. A radiochemical purity higher than 90% was achieved and remained unchanged for more than 4 h. The complex has a high stability in plasma, a moderate plasma protein binding and a moderate hydrophilicity. In vitro cell uptake studies showed a ratio between the activity taken up by cells in hypoxia/normoxia of 1.6 ± 0.4 (p < 0.5). Biodistribution in normal mice showed rapid depuration and low uptake in all organs and tissues except liver. Biodistribution in mice bearing induced tumours showed a low tumour uptake, but tumour/muscle ratio was favourable thanks to depuration. Comparison with biological results of other metronidazole derivatives clearly shows that modifications of the chelator are very important and contribute to improve the biological behaviour.

Mechanism of Tc toxin action revealed in molecular detail

Tripartite Tc toxin complexes of bacterial pathogens perforate the host membrane and translocate toxic enzymes into the host cell, including in humans. The underlying mechanism is complex but poorly understood. Here we report the first, to our knowledge, high-resolution structures of a TcA subunit in its prepore and pore state and of a complete 1.7 megadalton Tc complex. The structures reveal that, in addition to a translocation channel, TcA forms four receptor-binding sites and a neuraminidase-like region, which are important for its host specificity. pH-induced opening of the shell releases an entropic spring that drives the injection of the TcA channel into the membrane. Binding of TcB/TcC to TcA opens a gate formed by a six-bladed β-propeller and results in a continuous protein translocation channel, whose architecture and properties suggest a novel mode of protein unfolding and translocation. Our results allow us to understand key steps of infections involving Tc toxins at the molecular level.

Insights into Stabilization of the 99 Tc V O Core for Synthesis of 99 Tc V O Compounds

Synthesis of technetium-99 (99Tc; t1/2: 2.1 105 years, max: 253 keV) materials is of importance in studies of the nuclear fuel cycle where Tc is a major fission product (6percent thermal yield from 235U and 239Pu), in understanding radioactive tank waste composition, and in identifying 99mTc compounds for nuclear medicine imaging. One of the most useful synthetic starting materials, (NBu4)TcOCl4, is susceptible to disproportionation in water to form TcO4 and TcIV species, especially TcO2 2H2O. This unwanted reaction is especially problematic when working with ligands bearing hard donor atoms, such as oxygen, where the stability with the soft TcV=O3+ core may be low. Polyoxometalates (POMs) are such ligands. They possess defect sites with four hard oxygen atoms and show low (ca. 108) stability constants with transition metals. Tc complexes of POMs are molecular-level models for Tc metal oxide solid-state materials and can provide information on coordination and redox environments of metal oxides that stabilize low-valent Tc. In order to synthesize pure Tc POM complexes [TcVO(1-P2W17O61)]7 (TcVO-1) and [TcVO(2-P2W17O61)]7 (TcVO-2) from (NBu4)TcOCl4, we have identified strategies that minimize formation of TcIV species and optimize the formation of pure TcV species. The parameters that we consider are the amount of ethylene glycol,more » which is employed as a transfer ligand to prevent hydrolysis of (NBu4)TcOCl4, and the precipitating agent. The TcIV species that contaminates the non-optimized syntheses is likely a TcIV -oxido-bridged dimer [TcIV-(-O)2-TcIV]. We also employ a novel procedure where the 2 ligand is photoactivated and reduced (in the presence of a sacrificial electron donor) to subsequently reduce TcVIIO4 to an isolatable TcVO-2 product that is remarkably free of TcIV.« less

Re and (99m)Tc complexes of BodP3--multi-modality imaging probes.

A fluorescent tridentate phosphine, BodP3 (2), forms rhenium complexes which effectively image cancer cells. Related technetium analogues are also readily prepared and have potential as dual SPECT/fluorescent biological probes.

Toward Organometallic 99mTc Imaging Agents: Synthesis of Water-Stable 99Tc–NHC Complexes

(99)Tc(V)O2-NHC complexes containing monodentate and bidentate N-heterocyclic carbenes (NHCs) have been prepared by the reactions of [TcO(glyc)2](-) (glyc = ethyleneglycolato) with 1,3-dimethylimidazoline-2-ylidene (L1), 1,1'-methylene-3,3'-dimethyl-4,4'-diimidazoline-2,2'-diylidene (L2), and 1,1'-methylene-3,3'-diethyl-4,4'-diimidazoline-2,2'-diylidene (L3) in THF. The resulting complexes were fully characterized and their stabilities investigated. While complexes with monodentate NHCs only are hydrolytically unstable, complexes containing bidentate NHCs are water-stable over a broad pH range. The high water stability allows interconversion of the {(99)Tc(V)O2}(+) core into {(99)Tc(V)OCl}(2+) with HCl as the H(+) and Cl(-) source. An alternative procedure to obtain (99)Tc(V)O2-NHC complexes is the in situ deprotonation of imidazolium salts, enabling the preparation of (99)Tc(V)O2-NHC compounds without free NHCs, thus increasing the scope of NHC ligands drastically. The remarkable stability and pH-controllable reactivity of the new complexes underlines the potential of NHCs as stabilizing ligands for (99)Tc complexes and paves the way for the first (99m)Tc-NHC complexes in the future.

Chemical Design of 99mTc-Labeled Probes for Targeting Osteogenic Bone Region

Radionuclide bone imaging using polynuclear (99m)Tc complexes of bisphosphonates is the most common clinical practice in nuclear medicine. However, the improvement in the contrast between normal and osteogenic bone regions has been required. Herein we reported a new (99m)Tc-labeled compound considering the increased vascular permeability of osteogenic region. We selected penta-d-Asp as both a targeting motif to hydroxyapatite (HA) and a molecular size modifier, and two penta-d-Asp molecules were conjugated with the two carboxylate residues of ethylene dicysteine (EC) selected as the (99m)Tc chelating moiety to prepare EC-[(d-Asp)5]2. The molecular size, HA binding, and pharmacokinetics of (99m)Tc-EC-[(d-Asp)5]2 in normal mice and model rats bearing osteogenic tumor were compared to those of (99m)Tc-MDP and (99m)Tc-EC with one (d-Asp)5 motif, (99m)Tc-EC-(d-Asp)5. The molecular size of (99m)Tc-EC-[(d-Asp)5]2 was higher than that of (99m)Tc-MDP and (99m)Tc-EC-(d-Asp)5 when determined by permeability of the (99m)Tc-compounds through a membrane filter (10 kDa). The HA binding of (99m)Tc-EC-[(d-Asp)5]2 was higher than and similar to that of (99m)Tc-EC-(d-Asp)5 and (99m)Tc-MDP. (99m)Tc-EC-[(d-Asp)5]2 exhibited significantly lower accumulation in normal bone of mice than did (99m)Tc-MDP. In osteogenic tumor bearing model rats, (99m)Tc-EC-[(d-Asp)5]2 accumulated in the osteogenic and normal bone region similar to and lower than (99m)Tc-MDP, respectively. Although further studies including the chain length of d-Asp are required, these findings indicated that the present chemical design of (99m)Tc-labeled probe would be applicable to develop (99m)Tc-labeled probes for selective imaging of osteogenic bone region as well as develop therapeutic agents using therapeutic radionuclides such as (90)Y, (177)Lu, (186)Re, or (188)Re and cytotoxic agents to osteogenic bone tumor region.

NO Fluorescence Sensing by Europium Tetracyclines Complexes in the Presence of H2O2

The effect on the fluorescence of the europium:tetracycline (Eu:Tc), europium:oxytetracycline (Eu:OxyTc) and europium:chlortetracycline (Eu:ClTc) complexes in approximately 2:1 ratio of nitric oxide (NO), peroxynitrite (ONOO(-)), hydrogen peroxide (H2O2) and superoxide (O2 (·-)) was assessed at three ROS/RNS concentrations levels, 30°C and pH 6.00, 7.00 and 8.00. Except for the NO, an enhancement of fluorescence intensity was observed at pH 7.00 for all the europium tetracyclines complexes-the high enhancement was observed for H2O2. The quenching of the fluorescence of the Tc complexes, without and with the presence of other ROS/RNS species, provoked by NO constituted the bases for an analytical strategy for NO detection. The quantification capability was evaluated in a NO donor and in a standard solution. Good quantification results were obtained with the Eu:Tc (3:1) and Eu:OxyTc (4:1) complexes in the presence of H2O2 200μM with a detection limit of about 3μM (Eu:OxyTc).

Dithiocarbamate chitosan as a potential polymeric matrix for controlled drug release

Objective: To develop a polymer matrix for controlled release of drugs, chitosan, a linear aminopolysaccharide, was chemically modified to dithiocarbamate chitosan (DTCC) to afford a matrix where metal–drug complexes could be attached and released in a controlled manner depending on the binding nature between the drugs and the metals.Materials and methods: DTCC was treated with metal-tetracycline (Tc) complexes to prepare DTCC–Ca(II)–Tc, DTCC–Mg(II)–Tc, DTCC–Cu(II)–Tc and DTCC–Zn(II)–Tc.Results: The binding amount of Tc was in the order of DTCC–Zn(II)–Tc ≈ DTCC–Mg(II)–Tc ≈ DTCC–Ca(II)–Tc > DTCC–Cu(II)–Tc. The biphasic binding profiles, where Tc binding increased initially and then decreased, were shown for DTCC–Cu(II)–Tc and DTCC–Zn(II)–Tc. In a flow method, Tc was released slowly from DTCC–metal–Tc complexes except for DTCC–Cu(II)–Tc compared with Tc release from DTCC–Tc. In parallel with the results of the release experiment, DTCC–metal–Tc complexes except for DTCC–Cu(II)–Tc presented a prolonged antibacterial activity in an antibacterial test. The antibacterial activity of DTCC–Ca(II)–, –Mg(II)– and –Zn(II)–Tc complexes lasted for 28–44 days, while free Tc and DTCC–Tc lasted for 7–12 days.Discussion and conclusion: Taken together, our data suggest that DTCC could be used for a polymeric matrix for controlled release of drugs such as Tc, which possess functional groups for ionic and/or coordinate bond with metals.

A theoretical study of the mechanisms of oxidation of ethylene by manganese oxo complexes

The mechanisms of oxidation of ethylene by manganese-oxo complexes of the type MnO3L (L = O(-), Cl, CH3, OCH3, Cp, NPH3) have been explored on the singlet, doublet, triplet and quartet potential energy surfaces at the B3LYP/LACVP* level of theory and the results discussed and compared with those of the technetium and rhenium oxo complexes we reported earlier, thereby drawing group trends in the reactions of this important class of oxidation catalysts. In the reactions of MnO3L (L = O(-), Cl(-), CH3, OCH3, Cp, NPH3) with ethylene, it was found that the formation of the dioxylate intermediate along the concerted [3 + 2] addition pathway on the singlet potential energy is favored kinetically and thermodynamically over its formation by a two-step process via the metallaoxetane by [2 + 2] addition. The activation barriers for the formation of the dioxylate and the product stabilities on the singlet PES for the ligands studied are found to follow the order: NPH3 < Cl(-) < CH3O(-) < Cp < O(-) < CH3. On the doublet PES, the activation barriers for the formation of the dioxylate intermediate for the ligands are found to follow the order: CH3O(-) < Cl(-) < Cp < CH3 while the order of product stabilities is: Cl(-) < CH3O(-) < Cp < CH3. The order of dioxylate product stabilities on the triplet surface for the ligands studied is: Cl(-) < CH3O(-) < Cp < CH3 < NPH3 < O(-) and the order on the quartet surface is O(-) < Cp < CH3 < NPH3 < Cl(-) < CH3O(-). The re-arrangement of the metallaoxetane intermediate to the dioxylate is not a feasible reaction for all the ligands studied. Of the group VII B metal oxo complexes studied, MnO4(-) and MnO3(OCH3) appear to be the best catalysts for the exclusive formation of the dioxylate intermediate, MnO3(OCH3) being better so on both kinetic and thermodynamic grounds. The best epoxidation catalyst for the Mn complexes is MnO3Cl; the formation of the epoxide precursor will not result from the reaction of LMnO3 (L = O(-), Cp) with ethylene on any of the surfaces studied. The trends observed for the oxidation reactions of the Mn complexes with ethylene compare closely with those reported by us for the ReO3L and TcO3L (L = O(-), Cl, CH3, OCH3, Cp, NPH3) complexes, but there is far greater similarity between the Re and Tc complexes than between Mn and either of the other two. There does not appear to be any singlet-triplet or doublet-quartet spin-crossover in any of the pathways studied.

Three-component spectroelectrochemical sensor module for the detection of pertechnetate (TcO4-)

This review looks at the advancements in the development of a sensor for technetium (Tc) that is applicable to characterizing and monitoring the vadose zone and associated subsurface water. Subsurface contamination by Tc is of particular concern for two reasons: the extremely long lifetime of its most common isotope 99Tc (half-life = 2 x 105 years) and the fast migration in soils of pertechnetate (TcO4–) which is considered to be the dominant 99Tc species in ground water. TcO4– does not have a characteristic spectral signature which prevents its rapid, sensitive, and economic in-situ detection. To address this problem, a novel spectroelectrochemical sensor has been designed that combines three modes of selectivity (electrochemistry, spectroscopy, and selective partitioning) into a single sensor to substantially improve specificity which is critical in the specific detection of an analyte in the presence of potential interfering species. The sensor consists of a basic spectroelectrochemical configuration: a waveguide with an optically transparent electrode (OTE) that is coated with a thin chemically-selective film that preconcnetrates the analyte. The key to adapting this generic sensor to detect TcO4– and Tc complexes lies in the development of chemically-selective films that preconcentrate the analyte and, when necessary, chemically convert it intomore » a complex with electrochemical and spectroscopic properties appropriate for sensing. This review focuses on the general concept of the sensor and the rationale for the selection of the specific components of choice, the development and characterization of the sensor for the different detection modules, the synthesis and characterization of complexes relevant in the detection of technetium, and the progress in the utilization of the sensor module for the effective detection of these complexes.« less

The complexation of Tc(IV) with EDTA and picolinic acid at high pH

AbstractIn the UK, technetium may be disposed of in a high pH, low Eh cementitious repository. In such a scenario, its chemistry would be dominated by TcO4−, in aerobic conditions and the sparingly soluble TcO2(s)in anaerobic conditions. Repository heterogeneity could mean that both Tc(VII) and Tc(IV) are present simultaneously. The anthropogenic ligands EDTA and picolinic acid are commonly used as decontamination agents and are likely to be present in intermediate-level waste (ILW). They could complex with Tc(IV) increasing its aqueous concentration and mobility in the cement porewaters and beyond. The conditional stability constants (measured in 0.3 mol dm−3NaOH) for the Tc(IV)–EDTA and Tc(IV)–picolinic acid complexes have been determined to be: βTc(IV)−EDTA= 1.6 × 1026, which corresponds to log β = 25.2±0.6; and βTc(IV)−PA= 8.65 × 1026, which corresponds to log β = 26.9±0.1, respectively.

Complexation of Tc(IV) with EDTA at varying ionic strength of NaCl

Abstract The stability constant for Tc(IV)/EDTA complexes were determined using a solvent extraction technique at varying ionic strength (NaCl) and the specific ion interaction theory model allowed for calculating stability constants at zero ionic strength. The stability constants at zero ionic strength for the formation of the TcOEDTA2− and TcOHEDTA− complexes are 1020.0 ± 0.4 and 1025.3 ± 0.5, respectively. The modeled Tc(IV) solubility was calculated to be 3.9 × 10−7 M at near-neutral pH and in presence of 2.5 mM EDTA, a result found to be in good agreement with published solubility experimental data. Speciation calculations showed that TcOEDTA2− is the predominant species between pH 4 and 7.5 in presence of 0.171 mM EDTA, while TcO(OH)2 0 is predominant in basic solution. These studies show that EDTA has a very strong affinity for complexation with Tc(IV) and can increase the environmental mobility of Tc(IV).

ChemInform Abstract: Organometallic Complexes for SPECT Imaging and/or Radionuclide Therapy

AbstractReview: 245 refs.

Organometallic Complexes for SPECT Imaging and/or Radionuclide Therapy

This article reviews Re and Tc organometallic chemistry and radiochemistry, focusing on the most relevant aspects to design radiotools for molecular imaging and therapy. The review comprises an overview of organometallic Re and Tc complexes with relevance to the field, particularly M(I) tricarbonyl complexes stabilized by a huge variety of ligands. These include Werner type chelators, cyclopentadienyls, carboranes, and poly(mercaptoazolyl)borates, which permitted the hitherto unprecedented use of M–C and M–H bonds. The most relevant biomolecules labeled with the different organometallic cores will also be reviewed, as well as the opportunities offered by the tricarbonyl approach to design high-performance perfusion agents.

99Tc and Re Incorporated into Metal Oxide Polyoxometalates: Oxidation State Stability Elucidated by Electrochemistry and Theory

The radioactive element technetium-99 ((99)Tc, half-life = 2.1 × 10(5) years, β(-) of 253 keV), is a major byproduct of (235)U fission in the nuclear fuel cycle. (99)Tc is also found in radioactive waste tanks and in the environment at National Lab sites and fuel reprocessing centers. Separation and storage of the long-lived (99)Tc in an appropriate and stable waste-form is an important issue that needs to be addressed. Considering metal oxide solid-state materials as potential storage matrixes for Tc, we are examining the redox speciation of Tc on the molecular level using polyoxometalates (POMs) as models. In this study we investigate the electrochemistry of Tc complexes of the monovacant Wells-Dawson isomers, α(1)-P(2)W(17)O(61)(10-) (α1) and α(2)-P(2)W(17)O(61)(10-) (α2) to identify features of metal oxide materials that can stabilize the immobile Tc(IV) oxidation state accessed from the synthesized Tc(V)O species and to interrogate other possible oxidation states available to Tc within these materials. The experimental results are consistent with density functional theory (DFT) calculations. Electrochemistry of K(7-n)H(n)[Tc(V)O(α(1)-P(2)W(17)O(61))] (Tc(V)O-α1), K(7-n)H(n)[Tc(V)O(α(2)-P(2)W(17)O(61))] (Tc(V)O-α2) and their rhenium analogues as a function of pH show that the Tc-containing derivatives are always more readily reduced than their Re analogues. Both Tc and Re are reduced more readily in the lacunary α1 site as compared to the α2 site. The DFT calculations elucidate that the highest oxidation state attainable for Re is VII while, under the same electrochemistry conditions, the highest oxidation state for Tc is VI. The M(V)→ M(IV) reduction processes for Tc(V)O-α1 are not pH dependent or only slightly pH dependent suggesting that protonation does not accompany reduction of this species unlike the M(V)O-α2 (M = (99)Tc, Re) and Re(V)O-α1 where M(V/IV) reduction process must occur hand in hand with protonation of the terminal M═O to make the π*(M═O) orbitals accessible to the addition of electrons. This result is consistent with previous extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) data that reveal that the Tc(V) is "pulled" into the -α1 framework and that may facilitate the reduction of Tc(V)O-α1 and stabilize lower Tc oxidation states. This study highlights the inequivalency of the two sites, and their impact on the chemical properties of the Tc substituted in these positions.

Heteronuclear Gd-(99m)Tc Complex of DTPA-Bis(histidylamide) Conjugate as a Bimodal MR/SPECT Imaging Probe.

The work describes the synthesis and in vivo application of heterotrimetallic complexes of the type {Gd(H2O)[(M(H2O)(CO)3)2(1)]} {1 = DTPA-bis(histidyl-amide); M = Re (3a); (99m)Tc (3b)} for dual modality MR/SPECT imaging. Here, the DTPA-bis(histidylamide) conjugate functions as a trinucleating chelate incorporating Gd in the DTPA core with Re or (99m)Tc in the pair of histidylamide side arms. The two complexes are chemically equivalent as revealed by HPLC, and their "cocktail mixture" (3a + 3b) has demonstrated itself to be essentially a single bimodal imaging probe. The present system has thus overcome the sensitivity difference problem between MRI and SPECT and paved the way for practical applications.

Preincubation with Sn-complexes causes intensive intracellular retention of 99mTc in thyroid cells in vitro

Technetium radiopharmaceuticals are well established in nuclear medicine. Besides its well-known gamma radiation, (99m)Tc emits an average of five Auger and internal conversion electrons per decay. The biological toxicity of these low-energy, high-LET (linear energy transfer) emissions is a controversial subject. One aim of this study was to estimate in a cell model how much (99m)Tc can be present in exposed cells and which radiobiological effects could be estimated in (99m)Tc-overloaded cells. Sodium iodine symporter (NIS)-positive thyroid cells were used. (99m)Tc-uptake studies were performed after preincubation with a non-radioactive (cold) stannous pyrophosphate kit solution or as a standard (99m)Tc pyrophosphate kit preparation or with pure pertechnetate solution. Survival curves were analyzed from colony-forming assays. Preincubation with stannous complexes causes irreversible intracellular radioactivity retention of (99m)Tc and is followed by further pertechnetate influx to an unexpectedly high (99m)Tc level. The uptake of (99m)Tc pertechnetate in NIS-positive cells can be modified using stannous pyrophosphate from 3-5% to >80%. The maximum possible cellular uptake of (99m)Tc was 90Bq/cell. Compared with nearly pure extracellular irradiation from routine (99m)Tc complexes, cell survival was reduced by 3-4 orders of magnitude after preincubation with stannous pyrophosphate. Intracellular (99m)Tc retention is related to reduced survival, which is most likely mediated by the emission of low-energy electrons. Our findings show that the described experiments constitute a simple and useful in vitro model for radiobiological investigations in a cell model.

Synthesis and biological evaluation of a new triazole–oxotechnetium complex

A new triazole oxotechnetium chelating agent was synthesized via a 'Click-to-Chelate' strategy. In vivo evaluation of the corresponding (99m)Tc complex shows that the tracer exhibits very interesting properties for molecular imaging.