105Rh[1,5,9,13-tetrathiacyclohexadecane-3,11-diol] is a promising drug precursor for targeted radiotherapy. Nevertheless, the
axial position of chloride ions in the complex structure and their weak binding to rhodium centre, due to HSAB concept, make
such a complex subject to modifying action of certain sulphuric ligands, like human plasma thiol antioxidants: glutathione
and cysteine. Experiments were performed with both radioactive 105Rh and inactive rhodium. The complexation of rhodium with 1,5,9,13-tetrathiacyclohexadecane-3,11-diol (16S4diol) resulted in three distinct peaks seen on UV, radiometric and MS chromatograms. The substitution of chlorides was noted
in over 80% of 105[Rh(16S4diol)Cl2]+ units after incubation with glutathione, and less than 10% of complex units after incubation with cysteine (24 h, 37 °C).
Reaction of 105[Rh(16S4diol)Cl2]+ with 1,8-octandithiol and 1,9-nonandithiol resulted in disappearance of the complex peak and occurrence of two new peaks.
Product of RhCl3 and 16S4diol reaction is a mixture of three distinct forms having different number of chlorine atoms. Our in vitro experiments suggest
that the substitution of axial chlorides with glutathione and cysteine might also occur in vivo in human plasma. Glutathione
shows higher reactivity than cysteine in replacement reaction. Axial positions in precursor might be effectively blocked by
1,8-octandithiol and 1,9-nonandithiol.
. The average cross-section of the103Rh(n, 2n)102Rh reaction in a fission neutron spectrum is about 0.75 mb. Irradiation of rhodium in the bremsstrahlung spectrum of 50 MeV
electrons yielded a102Rh activity of 0.11 μCi/g after 3 days at a power of 2 kW. The thick target yield of the reaction104Pd(d, α)102Rh was 0.002 μCi/μAh for 12 MeV deuterons. The thick target yield of the reaction Ru(d,xn)102Rh was 0.05 μCi/μAh for 12 MeV deuterons and 4.8 μCi/μAh for 18 MeV deuterons. The best yield was obtained by deuteron bombardment
of ruthenium. The chemical separation of carrier-free Rh radionuclides from deuteron-irradiated ruthenium is described, with
a chemical yield better than 90%. The same procedure has also been applied for the isolation of105Rh from neutron-irradiated ruthenium. γ-Ray spectra of99Rh,101(m)Rh and102(m)Rh from deuteron-irradiated ruthenium and of105Rh from neutron-irradiated ruthenium, taken with a Ge(Li) detector, are shown; a number of γ-rays, not reported in the literature,
were observed. The γ-ray energies were determined with a precision of ca. 0.3–0.4 keV.
Authors:S. Thakare, A. Nair, S. Chakrabarty, and B. Tomar
An alternative reaction route for the production of111In from rhodium target bombarded with a12C beam has been developed. Sulfate fusion was adapted for dissolution of the irradiated rhodium metal target. Indium was coprecipitated
with La(OH)3 and purified by solvent extraction of the InBr3 complex into di-isopropyl ether and back extraction in 6M HCl. The chemical yield of the separation, determined using105Rh as tracer, was found to be above 90%. The radionuclidic purity of the separated111In satisfies the requirement prescribed for radiopharmaceutical preparations. The radioactivity yield achieved using this
route was about 0.2 MBq/μAh.