Dendrimers are branched nanomolecules, with a three dimensional structure, very low polydispersity and high functionality. Poly(amidoamine) (PAMAM) dendrimers are the most investigated class of dendrimers. In this study, PAMAM G4 dendrimer conjugated with HYNIC (hydrazinonicotinamide), an efficient bifunctional chelator, was characterized. Structure of the derivatized dendrimer was confirmed by (1)H-NMR and (13)C-NMR spectra and MALDI-TOF mass spectrometry. HYNIC-dendrimer was labeled with technetium-99m testing three different co-ligands (tricine, nicotinic acid and ethylenediaminodiacetic acid). The radiolabeled complexes were characterized by reverse phase HPLC, as well as their stabilities. Radiolabeling yield was about 99% with all co-ligands and complexes were found stable for 24 h. Biodistribution studies were performed administrating tricine-(99m)Tc-HYNIC-dendrimer, nicotinic acid-(99m)Tc-HYNICdendrimer and EDDA-(99m)Tc-HYNIC-dendrimer to normal mice; results showed blood clearance with hepatic and renal depuration in all cases. In this sense, labeling of PAMAM G4 dendrimer with technetium-99m using HYNIC could be obtained in high yield in a simple method and with high specific activity.
Owing to the rapid expansion of agriculture in South America in recent decades, soil erosion and fine 26 sediment supply to river networks, which lead to deleterious on-site and off-site environmental 27 impacts, are exacerbated in intensively cultivated catchments. Measuring soil inventories of bomb-28 derived fallout radiocesium ( 137 Cs) bound to fine particles is one of the few techniques available to reconstruct soil redistribution rates and evaluate the sustainability of farming practices over the recent 30 phase of agricultural intensification (1960s-2020). However, information about the spatial distribution 31 of 137 Cs fallout across the soils of South America remains scarce, and the published data has not been 32 synthesized at the scale of this subcontinent so far. The objective of the current research is therefore 33 to quantify and map the initial 137 Cs fallout at the scale of South America, based on the compilation of 34 published 137 Cs inventories, additional measurements conducted on undisturbed soil profiles and 35 digital soil mapping as this baseline information may be useful for a wide range of Earth Science 36 applications. A database of 137 Cs inventories at 96 reference sites (i.e. areas without soil erosion nor 37 accumulation) has been compiled for a variety of soil profiles (Argentina = 10, Brazil = 34, Chile = 46, 38 Uruguay = 5, French Guiana = 1) located between 5.3° North latitude and 53° South latitude. The spatial 39 distribution of 137 Cs fallout was shown to be highly latitude-dependent, with a maximum in the 30-50° 40 South latitude band. There were higher fallout levels than expected between 20 to 60° South latitude 41 compared to the previous estimations made by UNSCEAR. A partial least square regression approach 42 based on rainfall data and geographical information as covariates was used to create a baseline map 43 of 137 Cs fallout in soils of continental South America. This baseline map provides a powerful reference 44 dataset to anticipate the order of magnitude of 137 Cs inventories in undisturbed soil profiles collected 45 in Brazil and Southern Chile and for numerous other applications in Earth Sciences. The potential 46 application of the 137 Cs inventory technique in countries of South America in general, and in regions 47 investigate soil redistribution rates in most of South American countries where detectable levels of 52 137 Cs can be expected to be found in sites exposed to erosion.
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