Chromatographic separation of the theranostic radionuclide 111Ag from a proton irradiated thorium matrix

Eco-friendly and cost-effective adsorbent derived from blast furnace slag with black liquor waste for hazardous remediation

The current investigation concerns with preparation eco-friendly and cost-effective adsorbent (mesoporous silica nanoparticles (SBL)) based on black liquor (BL) containing lignin derived from sugarcane bagasse and combining it with sodium silicate derived from blast furnace slag (BFS) for thorium adsorption. Thorium ions were adsorbed from an aqueous solution using the synthesized bio-sorbent (SBL), which was then assessed by X-ray diffraction, BET surface area analysis, scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX), and Fourier transforms infrared spectroscopy (FTIR). Th(IV) sorption properties, including the pH effect, uptake rate, and sorption isotherms across various temperatures were investigated. The maximum sorption capacity of Th(IV) on SBL is 158.88 mg/L at pH value of 4328 K, and 60 min contact time. We demonstrated that the adsorption processes comport well with pseudo-second-order and Langmuir adsorption models considering the kinetics and equilibrium data. According to thermodynamic inspections results, the Th(IV) adsorption process exhibited endothermic and random behavior suggested by positive ΔH° and ΔS° values, while the negative ΔG° values indicated a spontaneous sorption process. The maximum Th(IV) desorption from the loaded SBL (Th/SBL) was carried out at 0.25 M of NaHCO3 and 60 min of contact. Sorption/desorption processes have five successive cycles. Finally, this study suggests that the recycling of BFS and BL can be exploited for the procurement of a promising Th(IV) adsorbents.

Chromatographic separation of silver-111 from neutron-irradiated palladium target: toward direct labeling of radiotracers

BACKGROUND

Silver-111 is a promising β--emitting radioisotope with ideal characteristics for targeted radionuclide therapy and associated single photon emission tomography imaging. Its decay properties closely resemble the clinically established lutetium-177, making it an attractive candidate for therapeutic applications. In addition, the clinical value of silver-111 is further enhanced by the existence of the positron-emitting counterpart silver-103, thus imparting a truly theranostic potential to this element. A so-fitting matching pair could potentially overcome the current limitations associated with the forced use of chemically different isotopes as imaging surrogates of lutetium-177, leading to more accurate and efficient diagnosis and treatment. However, the use of silver-111-based radiopharmaceuticals in vivo has faced obstacles due to the challenges related to its production and radiochemical separation from the target material. To address these issues, this study aims to implement a chromatographic separation methodology for the purification of reactor-produced silver-111. The ultimate goal is to achieve a ready-to-use formulation for the direct radiolabeling of tumour-seeking biomolecules.

RESULTS

A two-step sequence chromatographic process was validated for cold Ag-Pd separation and then translated to the radioactive counterpart. Silver-111 was produced via the 110Pd(n,γ)111Pd nuclear reaction on a natural palladium target and the subsequent β--decay of palladium-111. Silver-111 was chemically separated from the metallic target via the implemented chromatographic process by using commercially available LN and TK200 resins. The effectiveness of the separations was assessed by inductively coupled plasma optical emission spectroscopy and γ-spectrometry, respectively, and the Ag+ retrieval was afforded in pure water. Recovery of silver-111 was > 90% with a radionuclidic purity > 99% and a separation factor of around 4.21·10-4.

CONCLUSIONS

The developed separation method was suitable to obtain silver-111 with high molar activity in a ready-to-use water-based formulation that can be directly employed for the labeling of radiotracers. By successfully establishing a robust and efficient production and purification method for silver-111, this research paves the way for its wider application in targeted radionuclide therapy and precision imaging.

Tuning the Framework of Thioether-Functionalized Polyazamacrocycles: Searching for a Chelator for Theranostic Silver Radioisotopes

Silver-111 is an attractive unconventional candidate for targeted cancer therapy as well as for single photon emission computed tomography and can be complemented by silver-103 for positron emission tomography noninvasive diagnostic procedures. However, the shortage of chelating agents capable of forming stable complexes tethered to tumor-seeking vectors has hindered their in vivo application so far. In this study, a comparative investigation of a series of sulfur-containing structural homologues, namely, 1,4,7-tris[2-(methylsulfanyl)ethyl)]-1,4,7-triazacyclononane (NO3S), 1,5,9-tris[2-(methylsulfanyl)ethyl]-1,5,9-triazacyclododecane (TACD3S), 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclotridecane (TRI4S), and 1,4,8,11-tetrakis[2-(methylsulfanyl)ethyl]-1,4,8,11-tetraazacyclotetradecane (TE4S) was conducted to appraise the influence of different polyazamacrocyclic backbones on Ag+ complexation. The performances of these macrocycles were also compared with those of the previously reported Ag+/[111Ag]Ag+-chelator 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S). Nuclear magnetic resonance data supported by density functional theory calculations and X-ray crystallographic results gave insights into the coordination environment of these complexes, suggesting that all of the donor atoms are generally involved in the metal coordination. However, the modifications of the macrocycle topology alter the dynamic binding of the pendant arms or the conformation of the ring around the metal center. Combined pH/pAg-potentiometric and spectroscopic experiments revealed that the 12-member N4 backbone of DO4S forms the most stable Ag+ complex while both the enlargement and the shrinkage of the macrocyclic frame dwindle the stability of the complexes. Radiolabeling experiments, conducted with reactor-produced [111Ag]Ag+, evidenced that the thermodynamic stability trend is reflected in the ligand's ability to incorporate the radioactive ion at high molar activity, even in the presence of a competing cation (Pd2+), as well as in the integrity of the corresponding complexes in human serum. As a consequence, DO4S proved to be the most favorable candidate for future in vivo applications.

Lights and Shadows on the Sourcing of Silver Radioisotopes for Targeted Imaging and Therapy of Cancer: Production Routes and Separation Methods

The interest in silver radioisotopes of medical appeal (silver-103, silver-104m,g and silver-111) has been recently awakened by the versatile nature of their nuclear decays, which combine emissions potentially suitable for non-invasive imaging with emissions suited for cancer treatment. However, to trigger their in vivo application, the production of silver radioisotopes in adequate amounts, and with high radionuclidic purity and molar activity, is a key prerequisite. This review examines the different production routes of silver-111, silver-103 and silver-104m,g providing a comprehensive critical overview of the separation and purification strategies developed so far. Aspects of quality (radiochemical, chemical and radionuclidic purity) are also emphasized and compared with the aim of pushing towards the future implementation of this theranostic triplet in preclinical and clinical contexts.

Membrane assisted transport of thorium (IV) across bulk liquid membrane containing DEHPA as ion carrier: kinetic, mechanism and thermodynamic studies

Extraction and carrier mediated transport of thorium (IV) ions through bulk liquid membrane containing di-2-ethylhexyl phosphoric acid (DEHPA) in kerosene as metal ion carrier. The feed comprised of thorium (IV) ions solutions containing various concentrations of hydrochloric acid, while sulfuric acid solutions of different concentrations are used as a stripping agent. Various parameters about thorium (IV) ion extraction and transport were investigated: the feed solution acidity, initial metal ions aqueous solution concentration, carrier concentration and stripping agent concentration. More than 85% thorium (IV) is recovered in 960 min using 0.2 M DEHPA/kerosene as carrier and 1.5 M H2SO4 as stripping agent from the 0.0001 M HCl solution containing 50 mg L−1 thorium (IV) as feed. Assuming a consecutive, irreversible extraction and back-extraction (stripping) reactions a simple kinetic model was proposed for estimating the reaction rate constant or reaction rate coefficient under the investigated experimental conditions. The activation energy values of extraction and back-extraction reactions were calculated to be 29.94 kJ mol−1 and 20.55 kJ mol−1, respectively, which indicates that the extraction process was controlled by the mixed regime (both kinetic and diffusion), and the back-extraction process was mainly controlled by diffusion process.

SPECT/CT Imaging of 111Ag for the Preclinical Evaluation of Silver-Based Antimicrobial Nanomedicines

With the growing interest in developing silver-based antimicrobials, there is a need to better understand the behavior of silver within biological systems. To address this, we showed that single-photon emission computed tomography (SPECT) is a suitable method to noninvasively image 111Ag-labeled compounds in mice. Formed by neutron irradiation of palladium foil, 111Ag can be rapidly isolated with a high degree of purity and stably incorporated into antimicrobial silver nanoparticles. The imaging showed that nanoparticles are retained in the lungs for up to 48 h following intratracheal instillation, with limited uptake into the systemic circulation or organs of the reticuloendothelial system. Furthermore, in a mouse model of pulmonary Pseudomonas aeruginosa infection, the nanoparticles reduced the bacterial burden by 11.6-fold without inducing the production of pro-inflammatory mediators. Overall, SPECT imaging with 111Ag is a useful tool for noninvasively visualizing the biodistribution of silver-containing compounds in rodents. This knowledge of how silver nanoparticles distribute in vivo can be used to predict their therapeutic efficacy.

Highly Stable Silver(I) Complexes with Cyclen-Based Ligands Bearing Sulfide Arms: A Step Toward Silver-111 Labeled Radiopharmaceuticals

With a half-life of 7.45 days, silver-111 (β_max 1.04 MeV, E_γ 245.4 keV [I_γ 1.24%], E_γ 342.1 keV [I_γ 6.7%]) is a promising candidate for targeted cancer therapy with β^- emitters as well as for associated SPECT imaging. For its clinical use, the development of suitable ligands that form sufficiently stable Ag⁺-complexes in vivo is required. In this work, the following sulfur-containing derivatives of tetraazacyclododecane (cyclen) have been considered as potential chelators for silver-111: 1,4,7,10-tetrakis(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO4S), (2S,5S,8S,11S)-2,5,8,11-tetramethyl-1,4,7,10-tetrakis(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO4S4Me), 1,4,7-tris(2-(methylsulfanyl)ethyl)-1,4,7,10-tetraazacyclododecane (DO3S), 1,4,7-tris(2-(methylsulfanyl)ethyl)-10-acetamido-1,4,7,10-tetraazacyclododecane (DO3SAm), and 1,7-bis(2-(methylsulfanyl)ethyl)-4,10,diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S). Natural Ag⁺ was used in pH/Ag-potentiometric and UV-vis spectrophotometric studies to determine the metal speciation existing in aqueous NaNO₃ 0.15 M at 25 °C and the equilibrium constants of the complexes, whereas NMR and DFT calculations gave structural insights. Overall results indicated that sulfide pendant arms coordinate Ag⁺ allowing the formation of very stable complexes, both at acidic and physiological pH. Furthermore, radiolabeling, stability in saline phosphate buffer, and metal-competition experiments using the two ligands forming the strongest complexes, DO4S and DO4S4Me, were carried out with [¹¹¹Ag]Ag⁺ and promising results were obtained.

Chemical purification of 111Ag from isobaric impurity 111Cd by solid phase extraction chromatography: a proof of concept study

Silver-111 (¹¹¹Ag, t_1/2 = 7.47 d) is a β^- emitter suitable for targeted cancer therapy due to favourable decay properties. The production of no-carrier added ¹¹¹Ag via Isotope Separation On-Line (ISOL) technique is being investigated at the Legnaro National Laboratories of the Italian Institute of Nuclear Physics (ISOLPHARM project). Stable Cadmium-111 (¹¹¹Cd) is co-produced as isobaric contaminant, hence a chemical separation process must be developed to selectively harvest ¹¹¹Ag. In this study, a chromatographic procedure employing the commercially available CL resin was investigated by using stable Ag⁺ and Cd²⁺. Results indicate that CL resin allows to efficiently separate Ag⁺ from Cd²⁺ and recover the former with high yields.

Defining Processing Times for Accelerator Produced 225Ac and Other Isotopes from Proton Irradiated Thorium

During the purification of radioisotopes, decay periods or time dependent purification steps may be required to achieve a certain level of radiopurity in the final product. Actinum-225 (Ac-225), Silver-111 (Ag-111), Astatine-211 (At-211), Ruthenium-105 (Ru-105), and Rhodium-105 (Rh-105) are produced in a high energy proton irradiated thorium target. Experimentally measured cross sections, along with MCNP6-generated cross sections, were used to determine the quantities of Ac-225, Ag-111, At-211, Ru-105, Rh-105, and other co-produced radioactive impurities produced in a proton irradiated thorium target at Brookhaven Linac Isotope Producer (BLIP). Ac-225 and Ag-111 can be produced with high radiopurity by the proton irradiation of a thorium target at BLIP.

Separation of Protactinium Employing Sulfur-Based Extraction Chromatographic Resins

Protactinium-230 ( t_1/2 = 17.4 d) is the parent isotope of ²³⁰U ( t_1/2 = 20.8 d), a radionuclide of interest for targeted alpha therapy (TAT). Column chromatographic methods have been developed to separate no-carrier-added ²³⁰Pa from proton irradiated thorium targets and accompanying fission products. Results reported within demonstrate the use of novel sulfur bearing chromatographic extraction resins for the selective separation of protactinium. The recovery yield of ²³⁰Pa was 93 ± 4% employing a R₃P═S type commercially available resin and 88 ± 4% employing a DGTA (diglycothioamide) containing custom synthesized extraction chromatographic resin. The radiochemical purity of the recovered ²³⁰Pa was measured via high purity germanium γ-ray spectroscopy to be >99.5% with the remaining radioactive contaminant being ⁹⁵Nb due to its similar chemistry to protactinium. Measured equilibrium distribution coefficients for protactinium, thorium, uranium, niobium, radium, and actinium on both the R₃P═S type and the DGTA resin in hydrochloric acid media are reported, to the best of our knowledge, for the first time.

Selective biosorption of thorium (IV) from aqueous solutions by ginkgo leaf

Low-cost biosorbents (ginkgo leaf, osmanthus leaf, banyan leaf, magnolia leaf, holly leaf, walnut shell, and grapefruit peel) were evaluated in the simultaneous removal of La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Yb3+, Lu3+, UO22+, Th4+, Y3+, Co2+, Zn2+, Ni2+, and Sr2+ from aqueous solutions. In single metal systems, all adsorbents exhibited good to excellent adsorption capacities toward lanthanides and actinides. In a simulated multicomponent mixed solution study, higher selectivity and efficiency were observed for Th4+ over other metal cations, with ginkgo leaves providing the highest adsorptivity (81.2%) among the seven biosorbents. Through optimization studies, the selectivity of Th4+ biosorption on ginkgo leaf was found to be highly pH-dependent, with optimum Th4+ removal observed at pH 4. Th4+ adsorption was found to proceed rapidly with an equilibrium time of 120 min and conform to pseudo-second-order kinetics. The Langmuir isotherm model best described Th4+ biosorption, with a maximum monolayer adsorption capacity of 103.8 mg g-1. Thermodynamic calculations indicated that Th4+ biosorption was spontaneous and endothermic. Furthermore, the physical and chemical properties of the adsorbent were determined by scanning electron microscopy, Brunauer-Emmett-Teller, X-ray powder diffraction, and Fourier transform infrared analysis. The biosorption of Th from a real sample (monazite mineral) was studied and an efficiency of 90.4% was achieved from nitric acid at pH 4 using ginkgo leaves.

Separation of 103Ru from a proton irradiated thorium matrix: A potential source of Auger therapy radionuclide 103mRh

Ruthenium-103 is the parent isotope of ^103mRh (t_1/2 56.1 min), an isotope of interest for Auger electron therapy. During the proton irradiation of thorium targets, large amounts of ¹⁰³Ru are generated through proton induced fission. The development of a two part chemical separation process to isolate ¹⁰³Ru in high yield and purity from a proton irradiated thorium matrix on an analytical scale is described herein. The first part employed an anion exchange column to remove cationic actinide/lanthanide impurities along with the majority of the transition metal fission products. Secondly, an extraction chromatographic column utilizing diglycolamide functional groups was used to decontaminate ¹⁰³Ru from the remaining impurities. This method resulted in a final radiochemical yield of 83 ± 5% of ¹⁰³Ru with a purity of 99.9%. Additionally, measured nuclear reaction cross sections for the formation of ¹⁰³Ru and ¹⁰⁶Ru via the ²³²Th(p,f)^103,106Ru reactions are reported within.