(14)N quadrupolar coupling of amide nitrogen and Peptide secondary structure as studied by solid-state NMR spectroscopy.

To establish a relationship between the secondary structure of a peptide and the quadrupolar coupling of its amide (14)N, we examined (14)N quadrupolar couplings for eight different polypeptide samples, each of whose secondary structure (alpha-helix or beta-sheet) is known. The (14)N quadrupolar coupling is estimated from indirect observation of a (14)N overtone resonance under magic-angle spinning. From the observed indirect (14)N overtone spectra and calculated (14)N quadrupolar couplings for model molecules by using ab initio calculation (Gaussian03), it is shown that the quadrupolar coupling for the alpha-helix is larger than that for the beta-sheet by a few 100 kHz irrespective of the kind of amino acid residues examined (Ala, Val, Leu).

Association of europium(III), americium(III), and curium(III) with cellulose, chitin, and chitosan.

The association of trivalent f-elements-Eu(III), Am(III), and Cm(III)--with cellulose, chitin, and chitosan was determined by batch experiments and time-resolved, laser-induced fluorescence spectroscopy (TRLFS). The properties of these biopolymers as an adsorbent were characterized based on speciation calculation of Eu(III). The adsorption study showed that an increase of the ionic strength by NaCl did not affect the adsorption kinetics of Eu(III), Am(III), and Cm(III) for all the biopolymers, but the addition of Na2CO3 significantly delayed the kinetics because of their trivalent f-element complexation with carbonate ions. It also was suggested from the speciation calculation study that all the biopolymers were degraded under alkaline conditions, leading to their masking of the adsorption of Eu(III), Am(III), and Cm(III) on the nondegraded biopolymers. The masking effect was higher for cellulose than for chitin and chitosan, indicating that of the three, cellulose was degraded most significantly in alkaline solutions. Desorption experiments suggested that some portion of the adsorbed Eu(III) penetrated deep into the matrix, being isolated in a cavity-like site. The TRLFS study showed that the coordination environment of Eu(III) is stabilized mainly by the inner spherical coordination in chitin and by the outer spherical coordination in chitosan, with less association in cellulose in comparison to chitin and chitosan. These results suggest that the association of these biopolymers with Eu(III), Am(III), and Cm(III) is governed not only by the affinity of the functional groups alone but also by other factors, such as the macromolecular steric effect. The association of degraded materials of the biopolymers also should be taken into consideration for an accurate prediction of the influence of biopolymers on the migration behavior of trivalent f-elements.

Competitive inhibition and selectivity enhancement by Ca in the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, Hf) by carrot (Daucus carota cv. U.S. harumakigosun).

We investigated the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, and Hf) and the effect of Ca on their uptake in carrots (Daucus carota cv. U.S. harumakigosun) by the radioactive multitracer technique. The experimental results suggested that Na, Mg, K, and Rb competed for the functional groups outside the cells in roots with Ca but not for the transporter-binding sites on the plasma membrane of the root cortex cells. In contrast, Y, Ce, Pm, and Gd competed with Ca for the transporters on the plasma membrane. The selectivity, which was defined as the value obtained by dividing the concentration ratio of an elemental pair, K/Na, Rb/Na, Be/Sr, and Mg/Sr, in the presence of 0.2 and 2 ppm Ca by that of the corresponding elemental pair in the absence of Ca in the solution was estimated. The selectivity of K and Rb in roots was increased in the presence of Ca. The selectivity of Be in roots was not affected, whereas the selectivity of Mg was increased by Ca. These observations suggest that the presence of Ca in the uptake solution enhances the selectivity in the uptake of metabolically important elements against unwanted elements.

Association mechanisms of Europium(III) and Curium(III) with Chlorella vulgaris.

The association of Europium(III) (Eu[III]) and Curium(III) (Cm[III]) with Chlorella vulgaris and with cellulose was studied by a batch method and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The kinetics study performed by the batch method showed that maximum adsorption of Eu(III) and Cm(III) on C. vulgaris was attained within 3 min of contact; afterward, the percentage adsorption decreased with time due to chelation of the ions with exudates released from C. vulgaris with a strong affinity for Eu(III) and Cm(III). The TRLFS revealed that the short-term adsorption of Eu(III) on C. vulgaris was attributable to its coordination with cellulose on the algal cell wall. However, Eu(III) coordinated with the functional groups of cellulose very weakly despite the large distribution coefficients observed. These results indicate that the reactions, both at the cell's surfaces through adsorption and in solution phases through chelation with the exudates, are important in estimating the behavior of Eu(III) and Cm(III) in aqueous environments.

Adsorption of radionuclides on silica and their uptake by rice plants from silica-multitracer solutions: the effects of pH.

We investigated the effect of solution pH on the adsorption on silica of a mixture radionuclides 83Rb, 85Sr, 54Mn, 65Zn, 88Y, and 75Se generated from irradiation of Ag in a 135-MeV/nucleon 12C beam accelerated by the RIKEN Ring Cyclotron and 137Cs obtained commercially. Then, we related these findings to their uptake by a rice plant (Oryza sativa L. cv. Koshihikari) from a silica-multitracer solution at pH 4.3 +/- 0.2 and at 5.3 +/- 0.2. To evaluate both adsorption and uptake, precisely we used a multitracer technique that simultaneously tracked the movements of all of the radionuclides. There was an increase in the uptake of Rb, Cs, Sr, Mn, and Zn by the rice plants with the increase in pH from 4.3 to 5.3. By contrast, the uptake of Y and Se was less at the higher pH. Our findings suggest that the uptake of these elements is governed by their transport systems on the plasma membrane and by their affinity to silica, both of which are regulated by H+ concentration.

Uptake of trace elements by rice plants inoculated with Pyricularia oryzae.

The ability of rice plants inoculated with Pyricularia oryzae (P. oryzae) to take up trace elements was studied by the radioactive multitracer technique. Among various elements, only Mn, Co, Zn, Se, Rb, Sr, Tc, and Re were found to be transferred to rice shoots from soil. The concentrations of essential elements, Mn and Zn, in the shoots of rice plants inoculated with P. oryzae were slightly higher than those in the control plant shoots, while Se, Rb, Tc, and Re showed almost the same concentrations for both the shoots.

Chemical speciation and association of plutonium with bacteria, kaolinite clay, and their mixture.

We investigated the interactions of Pu(VI) with Bacillus subtilis, kaolinite clay, and a mixture of the two to determine and delineate the role of the microbes in regulating the environmental mobility of Pu. The bacteria, the kaolinite, and their mixture were exposed to a 4 x 10(-4) M Pu(VI) solution at pH 5.0. The amount of Pu sorbed by B. subtilis increased with time, but had not reached equilibrium in 48 h, whereas equilibrium was attained in kaolinite within 8 h. After 48 h, the oxidation state of Pu in the solutions exposed to B. subtilis and the mixture had changed to Pu-(V), whereas the oxidation state of Pu associated with B. subtilis and the mixture was Pu(IV). Exudates released from B. subtilis reduced Pu(VI) to Pu(V). In contrast, there was no change in the oxidation state of Pu in the solution or on kaolinite after exposure to Pu(VI). Scanning electron microscopy-energy dispersive spectrometry analysis indicated that most of the Pu in the mixture was associated with B. subtilis. These results suggest that Pu-(IV) is preferably sorbed to bacterial cells in the mixture and that Pu(VI) is reduced to Pu(V) and Pu(IV).

Effect of humic acid on the bioavailability of radionuclides to rice plants.

We investigated the effect of humic acid and solution pH on the uptake of the radionuclides, (83)Rb, (137)Cs, (54)Mn, (65)Zn, (88)Y, (102)Rh, and (75)Se in rice plants by the multitracer technique. The addition of humic acid to a culture medium containing SiO(2) increased the uptake of Mn and Zn at pH 4.3, whereas their uptake was decreased at pH 5.3. Humic acid depressed the uptake of Y at both pHs. The uptake of Se, which does not interact with humic acid, was not affected by its presence. These results suggest that uptake of the radionuclides by the rice plant is regulated by the affinity of radioactive nuclides for humic acid, as well as by the soil solution's pH.