Effect of pressure on pulse radiolysis reduction of proteins

From soil to cacao bean: Unravelling the pathways of cadmium translocation in a high Cd accumulating cultivar of Theobroma cacao L

The research on strategies to reduce cadmium (Cd) accumulation in cacao beans is currently limited by a lack of understanding of the Cd transfer pathways within the cacao tree. Here, we elucidated the transfer of Cd from soil to the nib (seed) in a high Cd accumulating cacao cultivar. Here, we elucidated the transfer of Cd from soil to the nib (seed) in a high Cd accumulating cacao cultivar through Cd stable isotope fractionation, speciation (X-Ray Absorption Spectroscopy), and localization (Laser Ablation Inductively Coupled Plasma Mass Spectrometry). The plant Cd concentrations were 10-28 higher than the topsoil Cd concentrations and increased as placenta< nib< testa< pod husk< root< leaf< branch. The retention of Cd in the roots was low. Light Cd isotopes were retained in the roots whilst heavier Cd isotopes were transported to the shoots (Δ ^114/110 Cd _shoot-root = 0.27 ± 0.02 ‰ (weighted average ± standard deviation)). Leaf Cd isotopes were heavier than Cd in the branches (Δ ^114/110 Cd _{IF3 leaves-branch} = 0.18 ± 0.01 ‰), confirming typical trends observed in annual crops. Nibs and branches were statistically not distinguishable (Δ ^114/110 Cd _nib-branch = -0.08‰ ± 0.06 ‰), contrary to the leaves and nibs (Δ ^114/110 Cd _{nib-IF3 leaves} = -0.25‰ ± 0.05 ‰). These isotope fractionation patterns alluded to a more direct transfer from branches to nibs rather than from leaves to nibs. The largest fraction (57%) of total plant Cd was present in the branches where it was primarily bound to carboxyl-ligands (60-100%) and mainly localized in the phloem rays and phelloderm of the bark. Cadmium in the nibs was mainly bound to oxygen ligands (60-90%), with phytate as the most plausible ligand. The weight of evidence suggested that Cd was transferred like other nutrients from root to shoot and accumulated in the phloem rays and phelloderm of the branches to reduce the transfer to foliage. Finally, the data indicated that the main contribution of nib Cd was from the phloem tissues of the branch rather than from leaf remobilization. This study extended the limited knowledge on Cd accumulation in perennial, woody crops and revealed that the Cd pathways in cacao are markedly different than in annual crops.

Mercury(II) Binding to Metallothionein in Mytilus edulis revealed by High Energy-Resolution XANES Spectroscopy

Of all divalent metals, mercury (HgII ) has the highest affinity for metallothioneins. HgII is considered to be enclosed in the α and β domains as tetrahedral α-type Hg4 Cys11-12 and β-type Hg3 Cys9 clusters similar to CdII and ZnII . However, neither the four-fold coordination of Hg nor the existence of Hg-Hg atomic pairs have ever been demonstrated, and the HgII partitioning among the two protein domains is unknown. Using high energy-resolution XANES spectroscopy, MP2 geometry optimization, and biochemical analysis, evidence for the coexistence of two-coordinate Hg-thiolate complex and four-coordinate Hg-thiolate cluster with a metacinnabar-type (β-HgS) structure in the α domain of separate metallothionein molecules from blue mussel under in vivo exposure is provided. The findings suggest that the CXXC claw setting of thiolate donors, which only exists in the α domain, acts as a nucleation center for the polynuclear complex and that the five CXC motifs from this domain serve as the cluster-forming motifs. Oligomerization is driven by metallophilic Hg⋅⋅⋅Hg interactions. Our results provide clues as to why Hg has higher affinity for the α than the β domain. More generally, this work provides a foundation for understanding how metallothioneins mediate mercury detoxification in the cell under in vivo conditions.

First observation of HO˙ reactivity in water under high energy ions at elevated temperature

This communication reports the first observation of the formation of HO˙ produced under two different High energy ion beams, (18)O(8+) and (36)Ar(18+) having Linear Energy Transfers (LET) of 65 and 350 eV nm(-1) respectively, at temperatures up to 411 K. Both scavenging with various concentrations of SCN(-) and heavy-ion pulse radiolysis methods are used with an original temperature and pressure regulated optical cell. Deconvolution of kinetics is used to analyze the evolution of HO˙ track segment yields as a function of time and temperature. It takes care of involving the ionic strength effect and Arrhenius expression in the rate constants correction. The results show a fast decay of HO˙ yields in the 10(-10)-10(-8) s range which denotes an efficient reactivity of this species in the track structure of the ion beam. This effect is enhanced with the lowest LET of O(8+). Increasing the temperature also accelerates the decays for both ions. These observations are discussed in terms of temperature activation of reactions and the track structure exhibiting the formation of HO˙ in a "low LET" penumbra around the ionization tracks. HO˙ track segment yields at 100 ns, of 0.4 × 10(-7) and 0.6 × 10(-7) mol J(-1), respectively for 350 and 65 eV nm(-1), are not affected by temperature.