Accumulation mechanisms of radiocaesium within lichen thallus tissues determined by means of in situ microscale localisation observation.

Many lichens are well known to accumulate radiocaesium and, thus acting as biomonitors of contamination levels. However, the actual localisation and chemical forms of radiocaesium in contaminated lichens have not yet been elucidated because, despite their high radioactivity, these forms are present in trace amounts as chemical entities. Here, we use autoradiography and demonstrate for the first time in situ microscale localisation of radiocaesium within thallus tissues to investigate the radiocaesium forms and their accumulation mechanism. Radiocaesium distributions showed similar trends in lichen tissues collected two and six years after the Fukushima nuclear accident. The radiocaesium was localised in the brown pigmented parts i.e., melanin-like substances, in the lower cortex of lichen thallus. Quantum chemical calculations showed that functional group of melanin-like substances can chelate Cs+ ion, which indicates that the Cs+ ions form complexes with the substances. Based on these findings, we suggest that radiocaesium ions may be retained stably in melanin-like substances for long periods (two to six years) due to steric factors, such as those seen in porphyrin-like structures and via multimer formation in the lower cortex. In addition, electron microscopy and autoradiography were used to observe radiocaesium-bearing microparticles (CsMPs) on/in the upper cortex and around the medullary layer. Micron-sized particles appeared to adhere to the surface tissue of the thallus, as shown by electron microscopy, suggesting that the particles were trapped by development of an adhesive layer; that is, CsMPs were trapped both physically and physiologically. These findings provide information on in situ localisation of two chemical forms of radiocaesium, cations and particles, in lichen thallus tissues and their accumulation mechanisms.

Quantum chemical calculation studies toward microscopic understanding of retention mechanism of Cs radioisotopes and other alkali metals in lichens.

We evaluate stability of cesium (Cs) and other alkali-metal cation complexes of lichen metabolites in both gas and aqueous phases to discuss why lichens can retain radioactive Cs in the thalli over several years. We focus on oxalic acid, (+)-usnic acid, atranorin, lecanoric acid, and protocetraric acid, which are common metabolite substances in various lichens including, e.g., Flavoparmelia caperata and Parmotrema tinctorum retaining Cs in Fukushima, Japan. By performing quantum chemical calculations, their gas-phase complexation energies and aqueous-solution complexation free energies with alkali-metal cations are computed for their neutral and deprotonated cases. Consequently, all the molecules are found to energetically favor cation complexations and the preference order is Li[Formula: see text]Na[Formula: see text]K[Formula: see text]Rb[Formula: see text]Cs[Formula: see text] for all conditions, indicating no specific Cs selectivity but strong binding with all alkali cations. Comparing complexation stabilities among these metabolites, lecanoric and protocetraric acids seen in medullary layer are found to keep higher affinity in their neutral case, while (+)-usnic acid and atranorin in upper cortex exhibit rather strong affinity only in deprotonated cases through forming stable six atoms' ring containing alkali cation chelated by two oxygens. These results suggest that the medullary layer can catch all alkali cations in a wide pH range around the physiological one, while the upper cortex can effectively block penetration of metal ions when the metal stress grows. Such insights highlight a physiological role of metabolites like blocking of metal-cation migrations into intracellular tissues, and explain long-term retention of alkali cations including Cs in lichens containing enough such metabolites to bind them.

A theoretical study of Ne3 using hyperspherical coordinates and a slow variable discretization approach.

We study theoretically the ground and excited bound states of the bosonic rare gas van der Waals trimer Ne(3). A slow variable discretization approach is adopted to solve the nuclear Schrödinger equation, in which the Schrödinger equation in hyperangular coordinates is solved using basis splines at a series of fixed finite-element methods discrete variable representation hyper-radii. We consider not only zero total nuclear orbital angular momentum, J = 0, states but also J > 0 states. By using the best empirical neon dimer interaction potentials, all the bound state energy levels of Ne(3) will be calculated for total angular momenta up to J = 6, as well as their average root-mean-square radii. We also analyze the wave functions in hyperspherical coordinates for several selected bound states.

Hyperspherical slow variable discretization method for weakly bound triatomic molecules.

We develop a method for calculating the bound state energies and the wave functions of weakly bound triatomic molecular systems. The method is based on the use of hyperspherical coordinates, combined with the slow variable discretization approach. The finite-element methods-discrete variable representation scheme provides an efficient means to solve the coupled-channel hyper-radial equations. Our method is applied to searching for bound states of the (20)Ne(2)H and (4)He(20)NeH triatomic molecules, using the best empirical pairwise interaction potentials. We consider not only zero total nuclear orbital momentum, J = 0, states but also J > 0 states. The (20)Ne(2)H system has been found to possess one bound state each for the J(Π)=0(+),1(-), and 2(+) symmetries, while there exist only one bound state for the (4)He(20)NeH system in the 0(+) symmetry. We shall calculate the bound state energies and analyze the molecular structures of these species in detail.

Adiabatic hyperspherical study of weakly bound He(2)H(-), He(2)H, and HeH(2) systems.

The He(2)H(-), He(2)H, and HeH(2) triatomic systems are studied using the adiabatic hyperspherical representation. By adopting the best empirical interaction potentials, we search for weakly bound states of (4)He(2) H(-), (4)He(2) H, and (4)HeH(2). We consider not only zero total nuclear orbital angular momentum, J=0, states but also J>0 states. We find no bound state for the (4)He(2) H systems, while the (4)He(2) H(-) and (4)HeH(2) systems are shown to possess three and one bound states, respectively, for J(Pi)=0(+). Interestingly, one bound state has been found each for the J(Pi)=1(-) and 2(+) symmetries of the (4)He(2) H(-) anion. We shall calculate the bound state energies and analyze the molecular structure of these species in detail.