Proton Competition Research Articles

Modulating conjugated microporous polymers via cyclization as a remarkable photo-enhanced uranium recovery platform

Uranium recovery is of great significance for managing environmental contamination, improving the utilization rate of uranium resources, reducing the pressure of nuclear fuel supply and building a closed-loop nuclear fuel cycle system. However, most of the current adsorbents are limited in practical application due to their poor selectivity in highly acidic environments (pH = 1). Here, we present a powerful uranium recovery strategy with combined ligand complexation, chemical reduction and photoreduction based on metal-free cyclization-modulated conjugated microporous polymers (CMPs). Our well-tailored CMP (CTATP-DHBA) is rich in pyridine and hydroquinone units, forming favorable six-membered chelation motifs to be well suited for selective loading and reduction of UVI, thus exhibiting remarkable uranium removal efficiency (ca. 83.27% removal in 200 ppm solutions, pH = 1). In the dark, CTATP-DHBA can effectively reduce pre-enriched UVI to UIV in situ via hydroquinone units on the skeleton, thus weakening the proton competition and achieving excellent uranium recovery efficiency. Meanwhile, the synergistic effect of the cyclized π-conjugated skeleton and the oxidized benzoquinone units significantly enhances the photocatalytic activity of CTATP-DHBA, and an additional UVI photocatalytic reduction can occur under visible light irradiation, enabling photo-enhanced uranium recovery. Environmental ImplicationThe mineralization of valence-variable radionuclides such as uranium could not only enhance the extraction performance and simplify the subsequent separation procedure, but also effectively weaken the competition of protons for selective sites in the acidic sample matrix. Thus, the construction of robust CMPs with excellent photoreduction activity and affinity may be an ideal material for the selective extraction and in-situ mineralization of strategic nuclide uranium from strongly acidic radioactive wastewater. Herein, a metal-free cyclization-modulated CMP with the favorable six-membered chelation motifs is tailor-made as an efficient platform for efficient extraction and in situ mineralization of valence-variable nuclide uranium.

Sorption of copper (II) ions by a composite sorbent based on chitosan and montmorillonite

A composite sorbent based on chitosan and montmorillonite has been developed for the extraction of heavy metal ions from aqueous solutions. The optimal chitosan / montmorillonite ratio for obtaining sorbent granules has been determined. Equilibriumkinetic studies of the process of copper (II) ions extraction in the heterophase system "aqueous solution of metal sulphate - modified sorbent" have been carried out.The treatment of sorption isotherms of copper (II) ions by the initial chitosan and a chitosan based composite according to the Langmuir equation made it possible to determine the maximum sorption capacities of these materials (А∞). It has been established that A∞ of the chitosan/montmorillonite composite sorbent exceeds the maximum sorption capacity for the original chitosan by more than two times.The effect of pH on the sorption of copper ions by chitosan-based sorbents is due to the competition of metal cations and protons for sorption sites. In the course of competitive chemisorption, protons deactivate amino groups - the main sorption centers, converting them into an inactive, H-salt form, which leads to a decrease in the sorption capacity of chitosan in relation to copper ions.Changes in the composition of the modified sorbent compared to the original chitosan are confirmed by infrared spectroscopy data. Microscopic studies using the method of scanning electron microscopy show the presence of changes in the surface structure of chitosan granules when montmorillonite is introduced into the composition of the sorbent.

Efficient Co-Adsorption and Highly Selective Separation of Cs+ and Sr2+ with a K+ -Activated Niobium Germanate by the pH Control.

137 Cs and 90 Sr are hazardous to ecological environment and human health due to their strong radioactivity, long half-life, and high mobility. However, effective adsorption and separation of Cs+ and Sr2+ from acidic radioactive wastewater is challenging due to stability issues of material and the strong competition of protons. Herein, a K+ -activated niobium germanate (K-NGH-1) presents efficient Cs+ /Sr2+ coadsorption and highly selective Cs+ /Sr2+ separation, respectively, under different acidity conditions. In neutral solution, K-NGH-1 exhibits ultrafast adsorption kinetics and high adsorption capacity for both Cs+ and Sr2+ (qm Cs = 182.91mg g-1 ; qm Sr = 41.62mg g-1 ). In 1M HNO3 solution, K-NGH-1 still possesses qm Cs of 91.40mg g-1 for Cs+ but almost no adsorption for Sr2+ . Moreover, K-NGH-1 can effectively separate Cs+ from 1M HNO3 solutions with excess competing Sr2+ and Mn + (Mn + = Na+ , Ca2+ , Mg2+ ) ions. Thus, efficient separation of Cs+ and Sr2+ is realized under acidic conditions. Besides, K-NGH-1 shows excellent acid and radiation resistance and recyclability. All the merits above endow K-NGH-1 with the first example of niobium germanates for radionuclides remediation. This work highlights the facile pH control approach towards bifunctional ion exchangers for efficient Cs+ /Sr2+ coadsorption and selective separation.

(Digital Presentation) Electrochemical and UV-VIS Spectroscopic Studies of Bismuth(III) Interactions with L-Cysteine

IntroductionIn an ongoing investigation of the interaction of bismuth(III) compounds with L-cysteiene1, recent work has involved more complete characterization of these interactions at lower pH levels in various aqueous media. Pharmaceutical medications2 such as bismuth subsalicylate (BSS) and bismuth citrate (BC) have now been investigated at pH 1.00 and 3.00 by both cyclic voltammetric and UV-VIS methods. Electrochemical methods have been used to evaluate the interaction of L-cysteine with bismuth compounds by observing shifts in the potential for bismuth reduction, and UV-VIS methods have allowed the observation of an absorbance peak at approximately 340 nm due to the bismuth(III) ion interaction with the L-cysteine thiol group.Results and DiscussionRecent work has involved investigation of bismuth(III) nitrate (BN), BSS, and BC with L-cysteine at pH 1.00 and 3.00 in both HNO3 and HCl solutions. In general, complexation of BN is not quite as favorable at lower pH levels as in pH 7.00 MOPS (3-N-morpholino)propanesulfonic acid)3 buffer solution.1 This conclusion was based on the need for higher mole ratios of L-cysteine to BN to achieve the final state of the voltammograms. The UV-VIS behavior was also not as well-defined as in our previous work1, with higher molar ratios of L-cysteine needed to produce the 340 nm absorbance peak. These results support the competition of protons with bismuth(III) for the L-cysteine ligand, there being much higher proton levels at pH 1.00 and pH 3.00 than at pH 7.00. The behaviors of BC and BSS at pH 1.00 and pH 3.00 are in many ways similar to that of BN. Finally, some preliminary work on glutathione (cysteine-containing tripeptide) interactions with bismuth compounds is also planned for presentation.References T. Cheek and D. Peña, J. Electrochem. Soc., 167, 155522 (2020)Li, R. Wang, and H. Sun, Acc. Chem. Res., 52, 216 (2019).M. H. Ferreira, I. S. S. Pinto, E. V. Soares, and H. M. V. M. Soares, RSC Advances, 5(39), 30989 (2015).

Evaluating the Effects of Metal Adduction and Charge Isomerism on Ion-Mobility Measurements using m-Xylene Macrocycles as Models.

Gas-phase ion-mobility spectrometry provides a unique platform to study the effect of mobile charge(s) or charge location on collisional cross section and ion separation. Here, we evaluate the effects of cation/anion adduction in a series of xylene and pyridyl macrocycles that contain ureas and thioureas. We explore how zinc binding led to unexpected deprotonation of the thiourea macrocyclic host in positive polarity ionization and subsequently how charge isomerism due to cation (zinc metal) and anion (chloride counterion) adduction or proton competition among acceptors can affect the measured collisional cross sections in helium and nitrogen buffer gases. Our approach uses synthetic chemistry to design macrocycle targets and a combination of ion-mobility spectrometry mass spectrometry experiments and quantum mechanics calculations to characterize their structural properties. We demonstrate that charge isomerism significantly improves ion-mobility resolution and allows for determination of the metal binding mechanism in metal-inclusion macrocyclic complexes. Additionally, charge isomers can be populated in molecules where individual protons are shared between acceptors. In these cases, interactions via drift gas collisions magnify the conformational differences. Finally, for the macrocyclic systems we report here, charge isomers are observed in both helium and nitrogen drift gases with similar resolution. The separation factor does not simply increase with increasing drift gas polarizability. Our study sheds light on important properties of charge isomerism and offers strategies to take advantage of this phenomenon in analytical separations.

EDTA analogues – unconventional inhibitors of gypsum precipitation

In the current study, EDTA (ethylenediamine-N,N,N′,N′-tetraacetic acid) and three further structurally related analogues with various spacing between the amino groups - PDTA (1,3-Diaminopropane-N,N,N′,N′-tetraacetic acid), HDTA (1,6-Diaminohexane-N,N,N′,N′-tetraacetic acid) and EGTA (Ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid) - were tested as inhibitors of gypsum crystallization. The precipitation reactions were performed at high initial supersaturation and calcium ions were present in large excess relative to the amount of the inhibitor. This way the crystallization reaction was facilitated and the degree of supersaturation was not affected by the complexation. It was found that the structural differences between the inhibitors (i.e., the spacing between the amino groups) seem to exert only a secondary effect on the efficiency of the inhibition. The optimum pH for inhibition was found to be strongly dependent on the inhibitor used. The optimum conditions for inhibition were explained in terms of the concentration of the uncomplexed ligand, which is determined by the stability of the calcium complexes with 1:1 composition as well as with the extent of proton competition. The structure, composition and morphology of the precipitating solids isolated from equilibrium mixtures at the completion of the precipitation process were also studied and the crystal faces where adsorption is most likely to happen were identified.

Symmetrical cyclo-N5- hydrogen bonds: stabilization mechanism of four non-metallic cyclo-pentazolate energetic salts.

Pairing different cations (R+) to stabilize cyclo-N5- is the main synthesis path for non-metallic cyclo-pentazolate (cyclo-N5-) salts. As novel energetic materials (EMs), crystalline packing-force of cyclo-N5- salts has been a puzzle, and whether cyclo-N5- is protonated also is a controversial issue. In this paper, four non-metallic cyclo-N5- salts, PHAC, N2H5N5, NH3OHN5, and NH4N5, are quantitatively studied by coupling first-principle method and bond-strength analyzing technology. Different from the traditional CHON-EMs (molecular crystal) and azide-EMs (ionic crystal), the four salts are stabilized by 3D hydrogen bond (HB) networks. One new type of hydrogen bond, protonated HB (p-H, R-H⋯N5-), is discovered to be a key stabilizing factor for cyclo-N5-. Proton competition mechanism between R and cyclo-N5- in p-H HB showed that cyclo-N5- cannot be protonated into HN5. In general, p-H HB can be adopted to estimate the stability of novel non-metallic cyclo-N5- EMs. Such findings have great significance for future design and performance prediction of novel cyclo-N5- EMs in both theoretical and experimental aspects.

Shaping the archipelago of stability by the competition of proton and neutron shell closures

The evolution of superheavy nuclei in proton and neutron number is explored by investigating the ground-state shell correction energy in the $Z=112\text{--}126$ and $N=170\text{--}190$ region of the $(Z,N)$ plane. Cuts through the $(Z,N)$-dependent distribution of shell corrections are chosen for constant neutron-proton differences as accessible in $\ensuremath{\alpha}$-decay chains and varying the neutron number at fixed charge number. A new approach is used, integrating elements of energy-density functional theory into the microscopic-macroscopic method. The topology of the shell correction implies for binding energies a distribution resembling in shape a ridge on a coral reef, formed by the competition of proton and neutron shell closures at $Z=114$ and $Z=120$, and $N=174$ and $N=184$, respectively. $^{288}\mathrm{Fl}$ is predicted as the next double magic nucleus after $^{208}\mathrm{Pb}$, and $^{304}120$ is identified as the most likely candidate for next-to-next double magic nucleus.

Proton Competition and Free Ion Activities Drive Cadmium, Copper, and Nickel Accumulation in River Biofilms in a Nordic Ecosystem

Biofilms can be used as a biomonitoring tool to determine metal bioavailability in streams affected by mining and other anthropogenic activities. Surface water and biofilm were sampled over two years from rivers located in the vicinity of a mine located in a Nordic ecosystem (Nunavik, Quebec). Biofilm metal content (Cd, Cu, and Ni) as well as a variety of physicochemical properties were determined to examine relationships between metal accumulation and water quality. Among the three metals of interest, copper and nickel had the highest levels of accumulation and cadmium had the lowest. When considering the exposure levels, nickel was the most abundant metal in our sampling sites. Both exposure and accumulation levels were consistent over time. Biofilm metal content was highly correlated to the ambient free metal ion concentration for sites of circumneutral pHs for all three metals. When the surface water pH was below 6, biofilm metal content was much lower than at other sites with similar aqueous metal concentrations of exposure. This apparent protective effect of decreasing pH can be explained by proton competition with dissolved metals for uptake binding sites at the surface of the organisms within the biofilm as described by the Biotic Ligand Model principles. The relationships obtained for Cd and Cu were overlapping those observed in previous publications, indicating strong similarities in metal accumulation processes in biofilms over very large geographical areas. Although more data are needed for Ni, our results show that biofilms represent a promising metal biomonitoring tool.

Comparison of APTES-Functionalized Silica Fiber and Clinoptilolite for Reducing Iron Concentrations in an Acidic Iron(II) Sulfate Solution: Potential Passive Treatment Substrates

Passive treatment systems provide lower cost alternatives for remediation of mine drainage; however, acidic drainage increases treatment difficulty because of higher metal concentrations and proton competition for reactive substrates. A silica fiber functionalized with (3-aminopropyl) triethoxysilane (Si + APTES) and a naturally-occurring, microporous silicate mineral (clinoptilolite of the zeolite family) were evaluated in the laboratory as potential reactive substrates for passive treatment of mild (≥ pH of 3) acid rock drainage. Column permeability experiments with spun, 10-µm median diameter, silica fiber and loosely packed, 3.6-mm median diameter clinoptilolite indicate greater permeability and stability of clinoptilolite under flowing conditions. Batch sorption experiments with silica fiber (Si), Si + APTES, and clinoptilolite in a synthetic Fe(II)–SO4, pH 3.0 solution indicate an Fe specific sorption efficacy of Si + APTES > clinoptilolite > Si at equivalent surface areas. Specific sorption normalized to packing densities indicate greater sorption per volume for clinoptilolite. Sorption results for Si + APTES and clinoptilolite did not produce isotherms described by the Langmuir or Freundlich models, likely because of surface heterogeneity and precipitation reactions. Column sorption experiments under flowing conditions indicate an Fe removal efficacy of clinoptilolite > Si + APTES for permeable packing densities. Si + APTES demonstrated high specific sorption of Fe in batch sorption experiments and has potential use in low-flow, passive treatment of mildly acidic solutions. The balance of minimal surface preparation, greater permeability, structural stability, large surface area, micropore structure, and ion-exchange properties make clinoptilolite a better reactive substrate for passive treatment of mildly acidic solutions in high- or low-flow conditions.

Characteristics of Cadmium Sorption by Heat-Activated Red Mud in Aqueous Solution

Red mud as a waste material is produced in large quantities by the aluminum industry. Heat activation has been used to enhance sorption capacity of red mud for its beneficial reuse as an effective sorbent. In this study, heat-activated red mud (HARM) was investigated for its Cd(II) sorption capacity under various process conditions (Cd concentration, pH and contact time) using response surface methodology (RSM). Analysis with RSM identified pH as the most important process parameter. The positive correlation between higher pH and greater Cd(II) sorption was likely due to: (i) decreased proton competition with Cd(II) for sorption sites at higher pH; (ii) enhanced sorption via ion exchange by monovalent Cd species from hydrolysis at higher pH; and (iii) improved thermodynamics of sorption at higher pH as protons are being released as products. Further analysis indicated the sorption process was thermodynamically favorable with a negative change in Gibbs free energy. Additionally, the sorption process exhibited a positive change in enthalpy, indicative of endothermic nature of sorption; this is consistent with sorption increase at higher temperature. These findings provide needed insight into the mechanisms underlying Cd(II) sorption by HARM for more effective applications of heat-activated red mud as sorbents for Cd(II) removal.

Copper(II) coordination properties of GxG peptides: Key role of side chains of central residues on coordination of formed systems; combined potentiometric and ITC studies

Abstract Isothermal titration calorimetry (ITC) and potentiometric titration (PT) methods were used to study the interactions of copper(II) ions with GAG, GDG, GKG, and GHG peptides. The calorimetric measurements were run in a MES buffer with the pH value of 6.0 at 298.15 K. Based on the results of PT data supported by theoretical calculations, the dissociation constants were calculated for the investigated peptides. The quantification of the proton competition with the metal for the peptide and incorporation it into the ITC data analysis enabled to obtain the pH-independent parameters, namely the binding constants (K) and the free energy of binding (ΔG). Furthermore, the relationship between the proposed coordination modes of the considered peptides and the thermodynamic parameters (K, ΔG and ΔH) has been discussed.

Impact of microbial activity on the mobility of metallic elements (Fe, Al and Hg) in tropical soils

Dissolved organic carbon (DOC), especially low molecular mass organic acids (LMMOAs) derives principally from biota degradation process in which soil microorganisms are the main actors and from roots exudates. The presence of LMMOAs led to an increase of availability and mobility of metallic elements through the formation of organo-metallic complex. In tropical soils, very few information about LMMOAs quantification and their role in the biogeochemical process related to trace metals cycling was available. Quantification of LMMOAs is limited due to their low concentration and rapid degradation. Until now, the role of microbial activity as well as LMMOAs in the biogeochemical cycle of metallic elements in tropical soils has not been investigated. The present study was conducted to evaluate the effect of microbial activity and biomass on the availability and mobility of metallic elements (Fe, Al and Hg) in two tropical soils, Ferralsol and Acrisol. We also quantified LMMOAs contents in soil solutions and addressed to their role in the mobilization of metals.Utilization of Diffuse Gradient in Thin film (DGT) method permits to analyze bioavailable metal in both fractions: organically complexed and free metals. The results show that the quantity of Fe, Al and Hg labile were higher in Ferralsol than Acrisol soils. This was more accentuated for the 50 cm-depth of soils where the microbial activities and the organic carbon content were important. Concentration of LMMOAs of Ferralsol and Acrisol were lower in compare to coniferous and deciduous forest soils. Proportions of LMMOAs in DOC were very small at 10.5% and 6.85% in the Ferralsol and Acrisol soils, respectively. The mobilization of Fe, Al and Hg in Ferralsol and Acrisol soils appeared to vary depending on the soil physico-chemical characteristics (sorption capacities and metals content) and also on the microbial biomass and activity. Soil pH influences the acidity of the functional groups in organic molecules and consequently their speciation. In addition, low pH increase proton competition within acidic functional groups involved in coordinate bond. The content of CEC in Ferralsol is higher than Acrisol that is related to the high contents of clay and organic carbon. Low CEC content can result in a decrease of retain of the cationic trace metals. Low CEC content led to a decrease of the capacity of retaining of metallic elements in tropical soils in compare to temperate soils.

Chemotherapeutic Drug Based Metal-Organic Particles for Microvesicle-Mediated Deep Penetration and Programmable pH/NIR/Hypoxia Activated Cancer Photochemotherapy.

A novel metal–organic particle (MOP) based nanodrug formed by mild self‐assembly of chemotherapeutic drugs, including banoxantrone and doxorubicin, through Cu(II)‐mediated coordination effects, is reported. In this nanodrug, Cu(II) acts as a bridge to join AQ4N and DOX, and then, self‐assembly of [‐AQ4N‐Cu(II)‐(DOX)2‐Cu(II)‐]n complexes forms nanosized MOPs (referred to as ADMOPs) through multiple interactions including host–metal–guest coordination, hydrophobic interactions, π‐stacking, and van der Waals force. The ADMOPs reported here have several important features over conventional drugs, including tumor microenvironment pH‐sensitive drug release that can be tracked by “turning on” the fluorescence of AQ4N or DOX through proton competition with Cu(II) to break the coordination bonds and much deeper penetration into solid tumors via microvesicle‐mediated intercellular transfer. Most strikingly, the ADMOPs can serve as stimuli‐responsive nanocarriers to efficiently load the photosensitizer phthalocyanine due to their inherent highly porous characteristics. Thus, the ADMOPs significantly enhance the chemotherapeutic efficacy by “on‐demand” photodynamic therapy, which further induces a hypoxic environment that enhances the reduction of AQ4N to systematically increase the therapeutic efficiency. Taken together, the designed ADMOPs composed of chemotherapeutic drugs may serve as a potential programmable controlled synergistic agent for cancer therapy.

Equilibrium Studies of Designed Metalloproteins.

Complete thermodynamic descriptions of the interactions of cofactors with proteins via equilibrium studies are challenging, but are essential to the evaluation of designed metalloproteins. While decades of studies on protein-protein interaction thermodynamics provide a strong underpinning to the successful computational design of novel protein folds and de novo proteins with enzymatic activity, the corresponding paucity of data on metal-protein interaction thermodynamics limits the success of computational metalloprotein design efforts. By evaluating the thermodynamics of metal-protein interactions via equilibrium binding studies, protein unfolding free energy determinations, proton competition equilibria, and electrochemistry, a more robust basis for the computational design of metalloproteins may be provided. Our laboratory has shown that such studies provide detailed insight into the assembly and stability of designed metalloproteins, allow for parsing apart the free energy contributions of metal-ligand interactions from those of porphyrin-protein interactions in hemeproteins, and even reveal their mechanisms of proton-coupled electron transfer. Here, we highlight studies that reveal the complex interplay between the various equilibria that underlie metalloprotein assembly and stability and the utility of making these detailed measurements.

High-spin structures of 77,79,81,83As isotopes

In this paper, we report comprehensive set of shell model calculations for arsenic isotopes. We performed shell model calculations with two recent effective interactions JUN45 and jj44b. The overall results for the energy levels and magnetic moments are in rather good agreement with the available experimental data. We have also reported competition of proton- and neutron-pair breakings analysis to identify which nucleon pairs are broken to obtain the total angular momentum of the calculated states. Further theoretical development is needed by enlarging model space by including [Formula: see text] and [Formula: see text] orbitals.

Investigations of copper(II) complexation by fragments of the FBP28 protein using isothermal titration (ITC) and differential scanning calorimetry (DSC)

Isothermal titration calorimetry (ITC) was used to study the interactions between copper(II) ions and peptides with sequences taken from the N-terminal loop of the FBP28 protein (formin-binding protein) WW domain: Ac-Lys-Thr-Ala-Asp-Gly-Lys-Thr-NH2 (D7) and Ac-Tyr-Lys-Thr-Ala-Asn-Gly-Lys-Thr-Tyr-NH2 (D9 M), respectively. Measurements were taken at 298.15 K in 20 mM 2-(N-morpholino)ethanesulfonic acid buffer solution at a pH of 6. The stoichiometry, conditional stability constants and thermodynamic parameters (ΔITCG, ΔITCH and ΔITCS) for the pertinent complexation reactions were determined. Furthermore, the thermal stability of peptide conformations in the presence and absence of copper(II) in the system was investigated using differential scanning calorimetry. Finally, a general procedure on how to include the effect of buffer competition with the peptide for the metal as well as proton competition with the metal for the peptide and the buffer’s component during ITC data analysis is described.

Intracellular localization, accumulation and distribution of heavy metals in plants

Heavy metals uptake, distribution and accumulation processes in plants are very important for their impact on physiological and biochemical processes and, consequently, on plant growth and development. The distribution of heavy metals in plant parts and cell organelles are discussed. There are detoxification mechanisms in cell compartments, like binding with cell wall, with organic acids in vacuoles, complexes with phytochelatins and etc. What proportion of given metal ions would be the in free form, and what – bound with organic molecules; it depends from pH of the environment and chemical properties of element. The stability of metals complexes decreases in the case of deviation pH of environment from neutral: at low pH there is a competition of protons with metal ions for binding sites in molecules, at high pH – by the reason of the competition of hydroxyl groups with ligand.

High-spin structures of 124−131Te: Competition of proton- and neutron-pair breakings

The 124-131Te nuclei have been produced as fission fragments in two fusion reactions induced by heavy-ions (12C + 238U at 90 MeV bombarding energy and 18O + 208Pb at 85 MeV) and studied with the Euroball array. Their high-spin level schemes have been extended to higher excitation energy from the triple gamma-ray coincidence data. The gamma-gamma angular correlations have been analyzed in order to assign spin and parity values to many observed states. Moreover the half-lives of isomeric states have been measured from the delayed coincidences between the fission-fragment detector SAPhIR and Euroball, as well as from the timing information of the Ge detectors. The behaviors of the yrast structures identified in the present work are first discussed in comparison with the general features known in the mass region, particularly the breakings of neutron pairs occupying the nuh11/2 orbit identified in the neighboring Sn nuclei. The experimental level schemes are then compared to shell-model calculations performed in this work. The analysis of the wave functions shows the effects of the proton-pair breaking along the yrast lines of the heavy Te isotopes.

Fractionation of yttrium and holmium during basaltic soil weathering

The anomalously low affinity of yttrium (Y) for iron (Fe) (oxyhydr)oxides relative to lanthanides with similar ionic radius (e.g., Ho) has been demonstrated in experiments with isolated Fe minerals and in a variety of marine systems that contain high concentrations of solid phase Fe. However, it has not previously been demonstrated to occur during soil genesis, despite the common observation that many soils become enriched in Fe over time. We hypothesized that Y would become progressively depleted in soils relative to Ho with increased weathering. Since, trivalent Y has an anomalously low Misono softness relative to other trivalent ions included in the rare earth element and yttrium group (REY3+), we also investigated whether soil REY fractionation reflects variation in Misono softness. To test this, we measured trends in total REY concentrations for Hawaiian soils derived from basaltic parent materials aged 0.3–4100ky, and measured REYs released from the same samples during short-time (3h) dissolution experiments conducted as part of a previous investigation linking dissolution with surface charge properties (Chorover et al., 2004). The chondrite-normalized Y/Ho ratios in the parent Hawaiian basalt (Chond[Y/Ho]=0.998) and continental dust (Chond[Y/Ho]=0.994) inputs are remarkably similar, and thus we can interpret deviations from Chond[Y/Ho]∼1.0 to result from soil biogeochemical processes and not source mixing. Between 0.3 and 20ky, the Chond[Y/Ho] ratio of the subsurface soils decreased from 0.96±0.07(2σ) to 0.71±0.05, and then remained unchanged across the rest of the weathering sequence. In contrast, the Chond[Y/Ho] ratio of the surface soils decreased from 0.99±0.07 to 0.76±0.05 at 150ky and then, most likely due to continued dust inputs, increased to 1.04±0.07 in the oldest soils. Analysis of the short-time dissolution experiments revealed preferential release of Y relative to Ho (and also La relative Pr) at intermediate pH where aqueous REY concentrations are governed by proton competition for adsorption sites. Proton-competition-control over REY release is bounded at high pH by the onset of colloidal dispersion—represented by the point of minimum dissolution (p.m.d.) of Al—and at low pH by the soil’s point of zero net charge (p.z.n.c.) and/or when proton-promoted dissolution of REY-containing solids, including Fe-(oxyhydr)oxides, control REY release. Results of our dissolution experiments suggest that complexation of REYs by dissolved organic matter (DOM) does not drive Y–Ho fractionation during pedogenesis, but rather may suppress it. Synthesis of these field and laboratory experiments suggests the Y/Ho ratio decreases early in soil development (<20ky) when weathering rates are high and competitive proton adsorption affects REY fractionation. Given that Fe-(oxyhydr)oxide sorbents exhibit greater affinity for Ho relative to Y, their prevalent neo-formation during incipient pedogenesis likely plays a central role in Y–Ho fractionation in these soils. Persistence of low Chond[Y/Ho] ratios in the subsurface soils even at 4100ky suggests Y–Ho fractionation continues, albeit at a slower rate, as weathering proceeds.