Inorganic Chemistry of the Tripodal Picolinate Ligand Tpaa with Gallium(III) and Radiolabeling with Gallium-68

We report here the improved synthesis of the tripodal picolinate chelator Tpaa, with an overall yield of 41% over five steps, in comparison to the previously reported 6% yield. Tpaa was investigated for its coordination chemistry with Ga(III) and radiolabeling properties with gallium-68 (68Ga). The obtained crystal structure for [Ga(Tpaa)] shows that the three picolinate arms coordinate to the Ga(III) ion, fully occupying the octahedral coordination geometry. This is supported by 1H NMR which shows that the three arms are symmetrical when coordinated to Ga(III). Assessment of the thermodynamic stability through potentiometry gives log KGa-Tpaa = 21.32, with a single species being produced across the range of pH 3.5-7.5. Tpaa achieved >99% radiochemical conversion with 68Ga under mild conditions ([Tpaa] = 6.6 μM, pH 7.4, 37 °C) with a molar activity of 3.1 GBq μmol-1. The resulting complex, [68Ga][Ga(Tpaa)], showed improved stability over the previously reported [68Ga][Ga(Dpaa)(H2O)] in a serum challenge, with 32% of [68Ga][Ga(Tpaa)] remaining intact after 30 min of incubation with fetal bovine serum

Chemische und physikalische Auswirkungen auf den Szilárd-Chalmers-Effekt am Beispiel des Molybdäns

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersSzilárd-Chalmers Reaktionen sind ein möglicher alternativer Weg zur Produktion des medizinisch wichtigen Radioisotops 99Mo. In dieser Arbeit wurden vier substituierte Molybdän(IV)oxophthalocyanine synthetisiert und mit Neutronen bestrahlt. Neben Aufreinigung, Charakterisierung und thermischer Analyse der Substanzen wurde auch die radiochemische Ausbeute an 99Mo sowie der Einfluss der Substituenten auf die Retention untersucht. Molybdän(IV)oxophthalocyanine wurden aus substituierten (-F, -NO2, -CH3) 1,2-Dicyanobenzol mit Ammoniumheptamolybdat-tetrahydrat bei ~170 °C in der Schmelze synthetisiert. Die Aufreinigung über Sublimation im Vakuum bei 450 °C und 0.06 mbar war für das unsubstituierte Molekül erfolgreich und ergab ein dunkelblaues Pulver. Alle synthetisierten Verbindungen wurden mittels IR, UV/VIS und Pulverdiffraktometrie charakterisiert. Die gemessene Mo=O Schwingung des unsubstituierten Molybdän(IV)oxophthalocyanins im IR (965 cm-1) und die berechnete Schwingung (994 cm-1) zeigen eine gute Übereinstimmung und weisen auf die erwartete Oxidationsstufe von +IV des Molybdäns hin. Die Abwesenheit der Mo≡N Schwingung bei 1078 cm-1 bestätigt dies. Die Bestrahlungsexperimente wurden in Trockenbestrahlungsrohren am Rande des Reaktorkerns (Neutronenfluss: 2·1012 cm-2s-1) des TRIGA Mark II Forschungsreaktors an der TU Wien durchgeführt. Die höchsten radiochemischen Ausbeuten wurden mit dem unsubstituierten Molybdän(IV)oxophthalocyanin erzielt, die höchsten Ausbeuten an trägerfreien 99Mo nach der Abtrennung konnten mit den NO2 und CH3 substituierten Verbindungen erreicht werden (> 90 %). Mögliche Substituenteneffekte wurden mittels Linear Free Energy Relationships (LFER; Hammett-Gleichung) untersucht. Es konnte kein Einfluss der Substituenten auf die radiochemische Ausbeute festgestellt werden, allerdings dürften Substituenteneffekte bei der Retention eine Rolle spielen. Möglicherweise verlaufen Rekombinationsreaktionen über eine positiv geladene Zwischenstufe - um eine gesicherte Aussage zu machen sind weitere Experimente notwendig. Von allen synthetisierten Verbindungen scheint das CH3 substituierte Molybdän(IV)oxophthalocyanin der vielversprechendste Kandidat bezüglich Synthese, Aufreinigung, Bestrahlung und Retention für weitere Untersuchungen zu sein.Szilárd-Chalmers reactions are a potential alternative route to the production of medically important 99Mo. In this work, four substituted molybdenum(IV) oxophthalocyanines were synthesised, irradiated and analysed regarding syntheses and purification, thermal stability, radiochemical yield of 99Mo in the target material and substitution effects on the retention. Molybdenum(IV) oxophthalocyanines were synthesized from substituted (-F, -NO2, -CH3) 1,2-dicyanobenzenes with ammonium heptamolybdate tetrahydrate in a melt at ~170 °C. Purification by sublimation at 450 °C and 0.06 mbar was successful for the unsubstituted material and gave a dark blue powder. The compounds were characterized by IR, UV/VIS and powder diffraction. The Mo=O vibration in IR spectra of the unsubstituted Molybdenum(IV) oxophthalocyanine (965 cm-1) and the calculated vibration at 994 cm-1 show good agreement and indicates the desired oxidation state of +IV for molybdenum - the absence of the Mo≡N vibration at 1078 cm-1 confirms this. Irradiation experiments were carried out in dry irradiation tubes at the edge of the core (neutron flux: 2·1012 cm-2s-1) of the TRIGA mark II research reactor at the TU Wien. The highest radiochemical yields were obtained with the unsubstituted Molybdenum(IV) oxophthalocyanine, whereas the highest yields of carrier-free 99Mo after separation were obtained with the NO2 and CH3 substituted phthalocyanines (>90 %). Using a Linear Free Energy Relationships (LFER; Hammett-equation) substitution effects during irradiation were investigated. No substituent effect were observed in the radiochemical yields, whereas an influence on the retention seems likely. It seems that the recombination reaction resulting in retention of the activated nucleus involves a positive charge, but further experiments are required. From the results obtained in this work the methyl-substituted molybdenum(IV) oxophthalocyanine is the most promising candidate regarding synthesis, purification, irradiation and retention for further investigations.3

Optimised production of technetium-94m for PET imaging by proton-irradiation of phosphomolybdic acid in cyclotron liquid target

Natural-abundance phosphomolybdic acid (H3(Mo12PO40) ‧12H2O, 0.181–0.552 g Mo/mL) solutions were irradiated with 12.9 MeV protons on a GE PETtrace cyclotron using an adapted standard liquid target. Technetium-94m (94mTc) was produced through the 94Mo(p,n)94mTc nuclear reaction with saturation yields of up to 53 ± 6 MBq/μA. End of bombardment activities of 161 ± 17 MBq and 157 ± 7 MBq were achieved for the 0.552 g Mo/mL solution (10 μA for 30 min) and 0.181 g Mo/mL solution (15 μA for 60 min), respectively. No visible degradation of the niobium target body and foil were seen during the irradiations of up to 15 μA for 60 min. The produced 94mTc was separated from the target phosphomolybdic acid solution with &gt;98% recovery using an aqueous biphasic extraction resin. Compared to previous reported liquid target methods for 94mTc production, the better production yield, in-target solution stability during irradiation and 94mTc separation recovery of phosphomolybdic acid makes it a very promising target material for routine clinical 94mTc production at medical facilities with liquid targets already installed for 18F production.</p

Measurement of the Th 229 Isomer Energy with a Magnetic Microcalorimeter

We present a measurement of the low-energy (0--60$\,$keV) $\gamma$ ray spectrum produced in the $\alpha$-decay of $^{233}$U using a dedicated cryogenic magnetic micro-calorimeter. The energy resolution of $\sim$$10\,$eV, together with exceptional gain linearity, allow us to measure the energy of the low-lying isomeric state in $^{229}$Th using four complementary evaluation schemes. The most accurate scheme determines the $^{229}$Th isomer energy to be $8.10(17)\,$eV, corresponding to 153.1(37)$\,$nm, superseding in precision previous values based on $\gamma$ spectroscopy, and agreeing with a recent measurement based on internal conversion electrons. We also measure branching ratios of the relevant excited states to be $b_{29}=9.3(6)\%$ and $b_{42}=0.3(3)\%$.Comment: 5 pages, 5 figures + supplementar

Efficient low-cost preparation of trans-cyclooctenes using a simplified flow setup for photoisomerization

Bioorthogonal ligations have emerged as highly versatile chemical tools for biomedical research. The exceptionally fast reaction between 1,2,4,5-tetrazines and trans-cyclooctenes (TCOs), also known as tetrazine ligation, is frequently used in this regard. Growing numbers of applications for the tetrazine ligation led to an increased demand for TCO compounds, whose commercial availability is still very limited. Reported photochemical procedures for the preparation of TCOs using flow chemistry are straightforward and high yielding but require expensive equipment. Within this contribution, we present the construction and characterization of a low-cost flow photoreactor assembled from readily accessible components. Syntheses of all commonly used trans-cyclooctene derivatives were successfully carried out using the described system. We are convinced that the presented system for photoisomerization will promote access to bioorthogonally reactive TCO derivatives