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Interaction between the Cesium Cation and Cesium Carboxylates: An Extended Cs+ Basicity Scale
ChemPlusChem
Abstract
The interaction between the cesium cation and fulvic or humic acids is supposed to play a role in cesium mobility in the environment, which is of importance in the context of geographical dispersion or concentration of the corresponding radionuclides. Among the singly charged positive clusters generated by electrospray ionization of mixtures of carboxylic acids (AH) and cesium salts (nitrate, iodide, or trifluoroacetate), the cluster [A−Cs+]Cs+[A′−Cs+] was subjected to collision-induced dissociation. The fragmentation into Cs+[A−Cs+] and Cs+[A′−Cs+] was treated using the kinetic method. A gas-phase basicity ladder was built by a step-by-step addition of the relative basicity data. The relative basicity scale deduced from the kinetic method was calibrated using the affinity and basicity (the enthalpy and Gibbs energy scales, respectively) obtained from DFT calculations. The enhanced basicity of the polyacid salts, relative to their monoacid salts, as well as the substituent effects on aliphatic and aromatic structures, are discussed.
... Energy-minimized PDB structures were used to prepare PDBQT files using MGL Tools 1.5.6. 49 A grid box with a dimension of 22 Å × 22 Å × 26 Å was centered at the Cartesian coordinates x = 20.217 Å, y = 20.008 ...
... It should be noted that many more values are available for other ligands, in particular, for Li + and Na + . 13,16,116,209 In addition, the kinetic method (K) has been used to determine the cesium cation affinities of many carboxylates (anchored there to an absolute scale) 210 and the relative affinities of many nitriles with Co + and Ni + . 211 Single temperature ICR equilibria (E) have also been used to measure the relative free energies for many of these ligands with CpNi + . ...
... The Free-Wilson method [59][60][61] was proposed by Flammang and coworkers [62] as a solution for such problems. The underlying mathematical concept, based on least squares optimization using linear regression analysis, was developed in a previous article [63]. This treatment provides the standard deviation on each interval and on the regression parameters as well as the correlation coefficient R (R 2 = fraction of variance explained by the model). ...
According to high level calculations, the upper part of the previously published FT-ICR lithium cation basicity (LiCB at 373 K) scale appeared to be biased by a systematic downward shift. The purpose of this work was to determine the source of this systematic difference. New experimental LiCB values at 373 K have been measured for 31 ligands by proton-transfer equilibrium techniques, ranging from tetrahydrofuran (137.2 kJ mol(-1)) to 1,2-dimethoxyethane (202.7 kJ mol(-1)). The relative basicities (ΔLiCB) were included in a single self-consistent ladder anchored to the absolute LiCB value of pyridine (146.7 kJ mol(-1)). This new LiCB scale exhibits a good agreement with theoretical values obtained at G2(MP2) level. By means of kinetic modeling, it was also shown that equilibrium measurements can be performed in spite of the formation of Li(+) bound dimers. The key feature for achieving accurate equilibrium measurements is the ion trapping time. The potential causes of discrepancies between the new data and previous experimental measurements were analyzed. It was concluded that the disagreement essentially finds its origin in the estimation of temperature and the calibration of Cook's kinetic method.
The reaction in water between CsOH and parabanic acid (PBH2) leads to the formation of the caesium salt of the oxalurate anion Cs(OXL), while the reaction with cyanuric acid (CYH3) leads to the formation of CsOH co-crystal of cyanuric acid Cs3(CYH3)4(OH)3. The X-ray crystal structure of these compounds shows that both the organic moieties OXL and CYH3 form robust homomeric ribbons based on strong and articulated N-H···O hydrogen bonds. The stabilization of the Cs+ ions can occur regardless of whether the ribbon of organic units is negatively charged or neutral. In Cs(OXL), each cation displays nine-fold coordination with Cs-O distances in the range 2.975(3) - 3.601(4) Å; in Cs3(CYH3)4(OH)3, two of the Cs+ cations (Cs1 and Cs2) display a nine-fold coordination with Cs-O distances in the range 3.007(9) – 3.823(13) Å and one (Cs3) is ten-fold coordinated with Cs-O distances in the range 3.161(14) – 3.653(17) Å. The molecular electrostatic potential maps of OXL and di-OXL anions have been reported and discussed.
Data on the gas-phase energetics of anion/cation interactions are relatively scarce. In this work, gas-phase alkali metal cation basicity (AMCB) scales were established for a series of 15 benzoate ions XC6H4COO- with Li+, Na+, K+, Rb+ and Cs+ on the basis of mass spectrometry experiments and high-level calculations. A wide range of electron-donating and electron-withdrawing substituents were included in the study. The thermochemical values were calculated by ab initio methodologies and extrapolated to the Complete Basis Set Limit. For each metal cation, the experimental relative cation basicity values of the anions were established quantitatively by applying the Cooks’ kinetic method to the cation-bound heterodimers [(XC6H4COO−)M+(YC6H4COO−)]−, generated by electrospray ionization. The self-consistency of these AMCB scales was ascertained by multiple overlap of the individual relative basicities. In parallel, the proton gas-phase basicities (GB) of the benzoate anions (gas-phase acidities of the respective benzoic acids) were calculated in order to compare the results of the theoretical method with known experimental GB values. The experimental and calculated GB values agree quite accurately (Average Absolute Deviation = 3.2 kJ mol-1). The relative experimental AMCB scales and the absolute calculated AMCB scales are highly correlated, and the two sets agree to better than 4 kJ mol-1. It is also demonstrated that the five series of calculated AMCB are highly correlated with calculated GB.
The formation and characterization of K+‐ and Cs+‐ complexes originating from the cooperativity of three non‐covalent interactions is explored. The tridimensional preorganization of the naphthothiophene platform displays a favourable well‐defined bay region combining a fragment and a carbonyl moiety flanking a central sulfur atom. A joint theoretical and experimental IRMPD study allowed deciphering the key contribution of the orthogonal phenyl fragment to the elaboration of alkali metal complexes. In combination with S‐ and CO‐interactions, the ‐cation interaction significantly enhances the binding energies of naphthothiophene derivatives.
In this review, noncovalent interactions of ions with neutral molecules are discussed. After defining the scope of the article, which excludes anionic and most protonated systems, methods associated with measuring thermodynamic information for such systems are briefly recounted. An extensive set of tables detailing available thermodynamic information for the noncovalent interactions of metal cations with a host of ligands is provided. Ligands include small molecules (H2, NH3, CO, CS, H2O, CH3CN, and others), organic ligands (O- and N-donors, crown ethers and related molecules, MALDI matrix molecules), π-ligands (alkenes, alkynes, benzene, and substituted benzenes), miscellaneous inorganic ligands, and biological systems (amino acids, peptides, sugars, nucleobases, nucleosides, and nucleotides). Hydration of metalated biological systems is also included along with selected proton-based systems: 18-crown-6 polyether with protonated peptides and base-pairing energies of nucleobases. In all cases, the literature thermochemistry is evaluated and, in many cases, reanchored or adjusted to 0 K bond dissociation energies. Trends in these values are discussed and related to a variety of simple molecular concepts.
TThe structure, relative stability and bonding of complexes formed by the interaction between Ga+ and a large set of compounds, including hydrocarbons, aromatic systems, and oxygen-, nitrogen-, fluorine and sulfur-containing Lewis bases have been investigated through the use of the high-level ab initio Gaussian-4 theory. Hence, a rather accurate Ga+ cation affinity (GaCA) and Ga+ cation basicity (GaCB) scales were established. Bonding analysis shows that, even though one of the main ingredients of the Ga+-base interaction is electrostatic, it exhibits a non-negligible covalent character triggered by the presence of the low-lying empty 4p orbital of Ga+ which favors a charge donation from occupied orbitals of the base to the metal ion. This partial covalent character, also observed in AlCA scales, is behind the dissimilarities observed when GaCA are compared with Li+ cation affinities, where covalent contributions are practically inexistent. Some dissimilarities between several Ga+-complexes and the Al+-analogues, mainly affecting the relative stability of π-complexes were found.
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In the past, basis sets for use in correlated molecular calculations have largely been taken from single configuration calculations. Recently, Almlöf, Taylor, and co‐workers have found that basis sets of natural orbitals derived from correlated atomic calculations (ANOs) provide an excellent description of molecular correlation effects. We report here a careful study of correlation effects in the oxygen atom, establishing that compact sets of primitive Gaussian functions effectively and efficiently describe correlation effects i f the exponents of the functions are optimized in atomic correlated calculations, although the primitive (s p) functions for describing correlation effects can be taken from atomic Hartree–Fock calculations i f the appropriate primitive set is used. Test calculations on oxygen‐containing molecules indicate that these primitive basis sets describe molecular correlation effects as well as the ANO sets of Almlöf and Taylor. Guided by the calculations on oxygen, basis sets for use in correlated atomic and molecular calculations were developed for all of the first row atoms from boron through neon and for hydrogen. As in the oxygen atom calculations, it was found that the incremental energy lowerings due to the addition of correlating functions fall into distinct groups. This leads to the concept of c o r r e l a t i o n c o n s i s t e n t b a s i s s e t s, i.e., sets which include all functions in a given group as well as all functions in any higher groups. Correlation consistent sets are given for all of the atoms considered. The most accurate sets determined in this way, [5s4p3d2f1g], consistently yield 99% of the correlation energy obtained with the corresponding ANO sets, even though the latter contains 50% more primitive functions and twice as many primitive polarization functions. It is estimated that this set yields 94%–97% of the total (HF+1+2) correlation energy for the atoms neon through boron.
The kinetic method is a widely used approach for the determination of thermochemical data such as proton affinities (PA) and gas-phase acidities (ΔH° ( acid )). These data are easily obtained from decompositions of noncovalent heterodimers if care is taken in the choice of the method, references used, and experimental conditions. Previously, several papers have focused on theoretical considerations concerning the nature of the references. Few investigations have been devoted to conditions required to validate the quality of the experimental results. In the present work, we are interested in rationalizing the origin of nonlinear effects that can be obtained with the kinetic method. It is shown that such deviations result from intrinsic properties of the systems investigated but can also be enhanced by artifacts resulting from experimental issues. Overall, it is shown that orthogonal distance regression (ODR) analysis of kinetic method data provides the optimum way of acquiring accurate thermodynamic information.
The tautomerism and aromaticity of 44 neutral and the corresponding 60 protonated azapentalenes were studied. The tautomerism was based on the calculated relative energies of the different tautomers, from two to three and nine nitrogen atoms. The aromaticity was estimated from the NICS values of both rings of azapentalenes. The possible relationship between both properties was assessed. The calculation was carried out at the B3LYP/6-311++G∗∗ computational level. MEP and NBO analysis were carried out on the studied compounds.Graphical abstract
Plant uptake of radiocaesium from soil is an important pathway for the entry of this pollutant into the human food chain and so contributes to any assessment of the radiation dose following contamination. Large differences in soil–plant transfer factors have been reported for plant species grown on the same soils. Few studies have attempted to distinguish between differences in root uptake and root-to-shoot translocation. We have investigated the root uptake of radiocaesium from artificially contaminated soils and the subsequent translocation to shoots for various plant species grown on three agricultural soils. The effects of short contact times and potassium starvation or enrichment have been studied. The Cs adsorption properties of rhizosphere soils have been compared with those of the initial soils. The proportion of activity removed from soil is largely soil dependent. Root uptake properties have less effect, but appear to be species determined, and not influenced by soil properties. Differences in soil-to-shoot transfer factor arise from species-dependent differences in root-to-shoot translocation. Root-to-shoot activity ratios are not soil dependent. There was little effect of soil potassium status. Root action slightly enhanced Cs adsorption on one soil, probably due to mineral weathering associated with the release of nonexchangeable potassium.
Plant developmental processes are controlled by internal signals that depend on the adequate supply of mineral nutrients by soil to roots. Thus, the availability of nutrient elements can be a major constraint to plant growth in many environments of the world, especially the tropics where soils are extremely low in nutrients. Plants take up most mineral nutrients through the rhizosphere where micro-organisms interact with plant products in root exudates. Plant root exudates consist of a complex mixture of organic acid anions, phytosiderophores, sugars, vitamins, amino acids, purines, nucleosides, inorganic ions (e.g. HCO3
–, OH–, H+), gaseous molecules (CO2, H2), enzymes and root border cells which have major direct or indirect effects on the acquisition of mineral nutrients required for plant growth. Phenolics and aldonic acids exuded directly by roots of N2-fixing legumes serve as major signals to Rhizobiaceae bacteria which form root nodules where N2 is reduced to ammonia. Some of the same compounds affect development of mycorrhizal fungi that are crucial for phosphate uptake. Plants growing in low-nutrient environments also employ root exudates in ways other than as symbiotic signals to soil microbes involved in nutrient procurement. Extracellular enzymes release P from organic compounds, and several types of molecules increase iron availability through chelation. Organic acids from root exudates can solubilize unavailable soil Ca, Fe and Al phosphates. Plants growing on nitrate generally maintain electronic neutrality by releasing an excess of anions, including hydroxyl ions. Legumes, which can grow well without nitrate through the benefits of N2 reduction in the root nodules, must release a net excess of protons. These protons can markedly lower rhizosphere pH and decrease the availability of some mineral nutrients as well as the effective functioning of some soil bacteria, such as the rhizobial bacteria themselves. Thus, environments which are naturally very acidic can pose a challenge to nutrient acquisition by plant roots, and threaten the survival of many beneficial microbes including the roots themselves. A few plants such as Rooibos tea (Aspalathus linearis L.) actively modify their rhizosphere pH by extruding OH– and HCO3
– to facilitate growth in low pH soils (pH 3 – 5). Our current understanding of how plants use root exudates to modify rhizosphere pH and the potential benefits associated with such processes are assessed in this review.
Uptake by roots from contaminated soil is one of the key steps in the entry of radiocaesium into the food chain. We have measured
the uptake by roots of radiocaesium and its transfer to shoots of a heathland grass, sheep fescue (Festuca ovina L.) from
two contrasting agricultural soils, a sandy podzol and a clayey calcareous soil. A culture device which keeps the roots separate
from the soil was used thus allowing rhizosphere soil to be obtained easily and enhancing the effect of root action. Biomass
production and 137Cs in shoots and roots were recorded. Cs adsorption was studied on both the initial, nonrhizosphere soil and on rhizosphere
soil in dilute soil suspension. Cs desorption was measured by resuspending subsamples of contaminated soil in solutions containing
various concentrations of stable Cs. The proportion of Cs fixed, i.e. not readily desorbable, was calculated by comparison
of the adsorption and desorption isotherms. Uptake by roots varied considerably between soils and did not appear to be diffusion
limited. Root-to-shoot transfer did not differ for the two soils studied. Root action considerably enhanced Cs adsorption
on the soils, particularly the in sandy podzol with a low Cs affinity. The value of Kd was increased by up to an order of magnitude. A large proportion of adsorbed Cs was found to be fixed, the Kd was up to seven times greater on desorption than adsorption, indicating that up to 80% of adsorbed Cs was not readily exchangeable.
Root action had little effect on the fixed fraction.
Soil organic matter consists of a highly complex and diversified blend of organic molecules, ranging from low molecular weight organic acids (LMWOAs), sugars, amines, alcohols, etc., to high apparent molecular weight fulvic and humic acids. The presence of a wide range of functional groups on these molecules makes them very reactive and influential in soil chemistry, in regards to acid–base chemistry, metal complexation, precipitation and dissolution of minerals and microbial reactions. Out of these functional groups, the carboxylic and phenolic ones are the most abundant and most influential in regards to metal complexation. Therefore, chemical equilibrium models have progressively dealt with organic matter in their calculations.
The corrected version of the paper is available at: http://www.pnas.org/content/108/49/19530.full.pdf+html?with-ds=yes.
(Abstract)
"The largest concern on the cesium-137 ((137)Cs) deposition and its soil contamination due to the emission from the Fukushima Daiichi Nuclear Power Plant (NPP) showed up after a massive quake on March 11, 2011. Cesium-137 ((137)Cs) with a half-life of 30.1 y causes the largest concerns because of its deleterious effect on agriculture and stock farming, and, thus, human life for decades. Removal of (137)Cs contaminated soils or land use limitations in areas where removal is not possible is, therefore, an urgent issue. A challenge lies in the fact that estimates of (137)Cs emissions from the Fukushima NPP are extremely uncertain, therefore, the distribution of (137)Cs in the environment is poorly constrained. Here, we estimate total (137)Cs deposition by integrating daily observations of (137)Cs deposition in each prefecture in Japan with relative deposition distribution patterns from a Lagrangian particle dispersion model, FLEXPART. We show that (137)Cs strongly contaminated the soils in large areas of eastern and northeastern Japan, whereas western Japan was sheltered by mountain ranges. The soils around Fukushima NPP and neighboring prefectures have been extensively contaminated with depositions of more than 100,000 and 10,000 MBq km(-2), respectively. Total (137)Cs depositions over two domains: (i) the Japan Islands and the surrounding ocean (130-150 °E and 30-46 °N) and, (ii) the Japan Islands, were estimated to be more than 5.6 and 1.0 PBq, respectively. We hope our (137)Cs deposition maps will help to coordinate decontamination efforts and plan regulatory measures in Japan."
It was recently reported that radioactive fallout due to the Fukushima Nuclear Accident was detected in environmental samples collected in the USA and Greece, which are very far away from Japan. In April-May 2011, fallout radionuclides ((134)Cs, (137)Cs, (131)I) released in the Fukushima Nuclear Accident were detected in environmental samples at the city of Krasnoyarsk (Russia), situated in the center of Asia. Similar maximum levels of (131)I and (137)Cs/(134)Cs and (131)I/(137)Cs ratios in water samples collected in Russia and Greece suggest the high-velocity movement of the radioactive contamination from the Fukushima Nuclear Accident and the global effects of this accident, similar to those caused by the Chernobyl accident.
The kinetic method is examined from the point of view of a proponent of a complementary and sometimes competitive technique, threshold collision-induced dissociation. Limitations in the kinetic method and assumptions that have not been thoroughly examined in the literature are pointed out. A case study involving recent experiments in the author's laboratory is used to illlustrate the importance of including entropic effects in the data analysis, even for systems where the ligands are fairly similar. The author concludes by encouraging the use of the advanced kinetic methods outlined by Cooks er al. in the accompanying Commentary. Copyright (C) 1999 by John Wiley & Sons, Ltd.
The unpolarized absorption and circular dichroism spectra of the
fundamental vibrational transitions of the chiral molecule,
4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields
are obtained using Density Functional Theory (DFT), MP2, and SCF
methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use
the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP)
density functionals. Mid-IR spectra predicted using LSDA, BLYP, and
B3LYP force fields are of significantly different quality, the B3LYP
force field yielding spectra in clearly superior, and overall excellent,
agreement with experiment. The MP2 force field yields spectra in
slightly worse agreement with experiment than the B3LYP force field. The
SCF force field yields spectra in poor agreement with experiment.The
basis set dependence of B3LYP force fields is also explored: the 6-31G
and TZ2P basis sets give very similar results while the 3-21G basis set
yields spectra in substantially worse agreements with experiment.
Low-molecular-weight (LMW) carboxylic acids found in soils and soil solutions comprise mainly aliphatic mono-, di- and tricarboxylic acids and substituted benzoic and cinnamic acids. This review compiles current information on the content of LMW carboxylic acids in soil solutions collected by centrifugation and in lysimeters, and soil extracts in relation to type of vegetation, soil type and soil depth. Contents of LMW carboxylic acids are highest in soil solution from the upper soil layers where carbon in LMW carboxylic acids constitutes up to 10% of DOC. The concentrations of aliphatic LMW di-/tricarboxylic acids (oxalic, malonic, malic, succinic, tartaric and citric acid) are usually in the range 0–50 μM with the higher concentrations in soil solutions from meadow, permanent pasture and forest soils as compared to ley and cultivated soils. In contrast, the concentrations of aliphatic LMW monocarboxylic acids (formic, acetic, propionic, butyric, valeric and lactic acid) are commonly in the range 0–1 mM with high concentrations found in soil solutions from both cultivated and forested soils. Especially insence cedar (Calocedrus decurrens (Torr.) Florin), ponderosa pine (Pinus ponderosa Dougl.), Douglas fir (Pseudotsuga menziesii Franco) and Norway spruce (Picea abies (L.) Karst.) seem to cause higher contents of LMW carboxylic acids in soils and soil solutions as compared to other tree species. Soil solution concentrations of substituted benzoic and cinnamic acids are submicromolar for all vegetations, whereas similar amounts in the range 0–800 μmol kg−1 of aliphatic LMW carboxylic acids and substituted benzoic and cinnamic acids are extractable from mineral soils with alkaline and dilute acid extractants. Seasonal variations are observed in soil solutions isolated by centrifugation and soil extracts with highest concentrations in 2–4 months in a period from mid spring to early summer, minimum concentrations around early autumn, and increasing concentrations during autumn.
Traces of short- and long-lived fallout 134Cs and 137Cs were found in surface soil (volcanic ash soil) under a cool-temperate deciduous stand at Tomakomai Experimental Forest in Hokkaido, Japan after the Fukushima nuclear accident in March 2011. Most of them were present in the uppermost 5–6 cm of the soil. Mean concentrations of 134Cs and 137Cs were found to be 2.4 (±0.3) and 89 (±2) Bq Kg−1 in May, and 6.9 (±0.4) and 94 (±2) Bq Kg−1 in November 2011, respectively. A small increase in radiocesium concentration may result from biological activity in the uppermost portion of the soil in which fallout nuclides derived from the Fukushima NPP would not have existed in May. They were supposed to be fallen down on the fresh litter layer in the previous year. The results of a sequential extraction experiment with 1 M CH3COONH4 solution showed that desorption of radiocesium from the soil was difficult and not simple ion exchange processes.
An analytical expression for the “effective temperature” parameter in the Cooks kinetic method is derived using classical Rice–Ramsperger–Kassel (RRK) theory for the microcanonical unimolecular dissociation rate. The approximate expression is appropriate for metastable ion dissociation experiments and high ion source temperatures. The effective temperature is directly proportional to the well depth (complexation energy) of the dissociating cluster ion, is inversely proportional to the number of oscillators of the cluster (vibrational degrees of freedom), and also depends on the product of the reaction frequency (preexponential factor) and the instrumental time window of the experiment. Numerical simulations using classical RRK rates with a detailed kinetics treatment are compared with the analytical expression for the effective temperatures. For fast dissociations (shallow cluster well depth or small number of oscillators), threshold effects cause significant curvature in the kinetic method plots. The implications of these results on the accuracy of relative thermochemical measurements by the kinetic method are discussed.
This review focuses on the quantitative data related to cesium cation interaction with neutral or negatively charged ligands. The techniques used for measuring the cesium cation affinity (enthalpies, CCA), and cesium cation basicities (Gibbs free energies, CCB) are briefly described. The quantum chemical calculations methods that were specifically designed for the determination of cesium cation adduct structures and the energetic aspects of the interaction are discussed. The experimental results, obtained essentially from mass spectrometry techniques, and complemented by thermochemical data, are tabulated and commented. In particular, the correlations between cesium cation affinities and lithium cation affinities for the various kinds of ligands (rare gases, polyatomic neutral molecules, among them aromatic compounds and negative ions) serve as a basis for the interpretation of the diverse electrostatic modes of interaction. A brief account of some recent analytical applications of ion/molecule reactions with Cs+, as well as other cationization approaches by Cs+, is given.
We studied Cs-137 contamination and radionuclide transfer in mountain forest ecosystems from Bulgaria. Here we show the first analyses of Cs-137 soil-to-plant transfer and we assess that it depends on the soil organic matter content and the specifics of the tree species. The forest litter is strong polluted with Cs-137 and is a barrier for its migration. In the upper 0-5 cm of the soil the Cs content ranges from 52 to 81 Bq kg−1 then decreases in deeper layers. The 1-year-old needles of spruce, fir, and Scots pine accumulate more cesium than the fine roots. The values of the needles transfer factor range between 0.3 and 0.58. The fine roots transfer factor varies between 0.1 and 0.32.
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Quasi-relativistic energy-adjusted ab initio pseudopotentials for the elements of groups 13-17 up to atomic number 53 (I) are presented together with corresponding energy-optimized valence basis sets. Test calculations for atomic excitation and ionization energies show the reliability of the derived pseudopotentials and basis sets.
239-240Pu and 137Cs activities in soil samples were measured in two sites of the littoral part of Côte d'lvoire: Abidjan and the classified forest of "la Comoé". Two areas were chosen: a forest and a clearing. The aim of this work is to establish a starting point for nuclear contamination data of a non-nuclear country. Measured soil cores were of 10 cm depth.137Cs and 239-240Pu activities, mainly due to weapon nuclear tests in the 1960s, were in the range 0.37-2.3 and 0.023-0.125 Bq kg-1 respectively. 239-240Pu/137CS values were found to be about 0.024―0.19 in agreement with the expected value for nuclear tests
Effect of intense rainfall on the distribution of Fukushima-accident-derived 137Cs in soil was examined. Inventories and vertical distributions of 137Cs in soils were determined at 15 locations (including croplands, grasslands, and forests) in Fukushima city in the post-rainy season, approximately 4.5 months after the accident, and were compared with those in the pre-rainy season determined in our former study. The 137Cs inventory levels scarcely changed between points in time spanning the first rainy season after the accident. Moreover, the majority of 137Cs remained stored in the aboveground vegetation and in the upper 5 cm of soil layer at undisturbed locations in the post-rainy season. A more quantitative analysis with the characterization of the vertical profile of 137Cs using the relaxation length confirmed that the vertical profile was almost unchanged at most locations. Accordingly, it is concluded that rainfall during the rainy season had a limited effect on 137Cs distribution in the soil, indicating the very low mobility. Chemical extraction of 137Cs from selected soil samples indicated that 137Cs in the soil was barely water soluble, and even the fraction extracted with 1 M ammonium acetate was only approximately 10%. This further supports the low mobility of 137Cs in our soils. Soil mineralogical analyses, which included the identification of clay minerals, suggested that smectite and mica could lower the exchangeable fraction of 137Cs. However, no direct relationship was obtained between mineral composition and 137Cs retention in the upper soil layer. In contrast, positive correlations were observed between 137Cs extractability and soil properties such as pH, organic matter content, finer-sized particle content, and cation-exchange capacity. These results suggest that the mineralogical effect on the firm fixation of 137Cs on soil constituents may be masked by the non-specific adsorption offered by the physicochemical properties of the soils.
The accident at the Fukushima Dai-ichi Nuclear Power Plant has resulted in radioactive contamination of environmental media and food in the Far East of Russia, particularly in the Sakhalin Region. To obtain the knowledge about the (134)Cs and (137)Cs spatial distribution in the Sakhalin Region, soil samples were collected at 31 representative grassland sites on Sakhalin, Kunashir and Shikotan islands (43.80°-46.40° N and 142.73°-146.84° E) in the middle of May and around the end of September to early October 2011. In the autumn, vegetation samples (mixed grass/forb crop and bamboo, Sasa sp.) were collected together with soil samples. Maximum measured activity concentrations (on dry weight) of (134)Cs and (137)Cs in soil were 30 Bq kg(-1) and 210 Bq kg(-1), respectively. Within soil profile, (134)Cs activity concentrations declined rapidly with depth. Although for both sampling occasions (in the spring and autumn) the radionuclide was completely retained in the upper 3-4 cm of soil, a deeper penetration of the contaminant into the ground was observed in the autumn. In contrast with (134)Cs, activity concentrations of (137)Cs demonstrated a broad range of the vertical distribution in soil; at most sites, the radionuclide was found down to a depth of 20 cm. This resulted from interfering the aged pre-accidental (137)Cs and the new Fukushima-borne (137)Cs. To calculate contribution of these sources to the inventory of (137)Cs, the (134)Cs:(137)Cs activity ratio of 1:1 in Fukushima fallout (the reference date 15 March 2011) was used. The maximum deposition density of Fukushima-derived (137)Cs was found on Shikotan and Kunashir Islands with average density of 0.124 ± 0.018 kBq m(-2) and 0.086 ± 0.026 kBq m(-2), respectively. Sakhalin Island was less contaminated by Fukushima-derived (137)Cs of 0.021 ± 0.018 kBq m(-2). For the south of Sakhalin Island, the reference inventory of pre-Fukushima (137)Cs was calculated as 1.93 ± 0.25 kBq m(-2) (reference date 15 March 2011). For Shikotan and Kunashir Islands, the pre-Fukushima reference levels of (137)Cs ground contamination appeared to be higher: on average, 2.81 ± 0.35 kBq m(-2). Maximum measured activity concentrations (on wet weight) of (134)Cs and (137)Cs in the vegetation were 5 Bq kg(-1) and 18 Bq kg(-1), respectively. Soil-to-plant aggregated transfer factors, T(ag)s, for (134)Cs were more than an order of magnitude higher than those for (137)Cs. For the above-ground biomass density of 1 kg per m(2) (wet weight), plant contamination may contribute approximately 2% and 0.1% to the ground deposition of Fukushima-derived and pre-accidental (137)Cs, respectively.
The chemistry community now recognizes the cation-π interaction as a major force for molecular recognition, joining the hydrophobic effect, the hydrogen bond, and the ion pair in determining macromolecular structure and drug-receptor interactions. This Account provides the author's perspective on the intellectual origins and fundamental nature of the cation-π interaction. Early studies on cyclophanes established that water-soluble, cationic molecules would forego aqueous solvation to enter a hydrophobic cavity if that cavity was lined with π systems. Important gas phase studies established the fundamental nature of the cation-π interaction. The strength of the cation-π interaction (Li(+) binds to benzene with 38 kcal/mol of binding energy; NH(4)(+) with 19 kcal/mol) distinguishes it from the weaker polar-π interactions observed in the benzene dimer or water-benzene complexes. In addition to the substantial intrinsic strength of the cation-π interaction in gas phase studies, the cation-π interaction remains energetically significant in aqueous media and under biological conditions. Many studies have shown that cation-π interactions can enhance binding energies by 2-5 kcal/mol, making them competitive with hydrogen bonds and ion pairs in drug-receptor and protein-protein interactions. As with other noncovalent interactions involving aromatic systems, the cation-π interaction includes a substantial electrostatic component. The six (four) C(δ-)-H(δ+) bond dipoles of a molecule like benzene (ethylene) combine to produce a region of negative electrostatic potential on the face of the π system. Simple electrostatics facilitate a natural attraction of cations to the surface. The trend for (gas phase) binding energies is Li(+) > Na(+) > K(+) > Rb(+): as the ion gets larger the charge is dispersed over a larger sphere and binding interactions weaken, a classical electrostatic effect. On other hand, polarizability does not define these interactions. Cyclohexane is more polarizable than benzene but a decidedly poorer cation binder. Many studies have documented cation-π interactions in protein structures, where lysine or arginine side chains interact with phenylalanine, tyrosine, or tryptophan. In addition, countless studies have established the importance of the cation-π interaction in a range of biological processes. Our work has focused on molecular neurobiology, and we have shown that neurotransmitters generally use a cation-π interaction to bind to their receptors. We have also shown that many drug-receptor interactions involve cation-π interactions. A cation-π interaction plays a critical role in the binding of nicotine to ACh receptors in the brain, an especially significant case. Other researchers have established important cation-π interactions in the recognition of the "histone code," in terpene biosynthesis, in chemical catalysis, and in many other systems.
We assess various approximate forms for the correlation energy per particle of the spin-polarized homogeneous electron gas that have frequently been used in applications of the local spin density approximation to the exchange-correlation energy functional. By accurately recalculating the RPA correlation energy as a function of electron density and spin polarization we demonstrate the inadequacies of the usual approximation for interpolating between the para- and ferro-magnetic states and present an accurate new interpolation formula. A Padé approximant technique is used to accurately interpolate the recent Monte Carlo results (para and ferro) of Ceperley and Alder into the important range of densities for atoms, molecules, and metals. These results can be combined with the RPA spin-dependence so as to produce a correlation energy for a spin-polarized homogeneous electron gas with an estimated maximum error of 1 mRy and thus should reliably determine the magnitude of non-local corrections to the local spin density approximation in real systems.
Noncovalent interactions are essential for the existence of solid and liquid phases. Traditionally touted as weak forces, quantification of these interactions, which govern the molecular aggregation and determine the supramolecular assembly, is of fundamental interest. Hydrogen bonding has been extremely well studied and recognized as the most important of all noncovalent interactions. Calixarenes, which are cyclic oligomers obtained from condensation of formaldehyde with para-alkylphenols under alkaline conditions, form a class of host molecules explored in a large number of studies because of their ability to form inclusion complexes governed by cation-π interactions. Chiral calixarene analogues, constructed by changing the methylene moiety to a chiral unit provide the possibility of enantiomeric selectivity toward chiral guests.
A sample of ombrotrophic peat from Moor House in northern England was extensively extracted with dilute nitric acid (pH 1) to free it of bound cations. Suspensions of the acid-washed peat (5-30 g l(-1)), prepared with different concentrations of background electrolyte (NaCl and KCl), were used to conduct batch acid-base titrations. A strong dependence of proton release on ionic strength (I) was observed, the apparent acid dissociation constant (pK(app)) being found to decrease by approximately 1.0 for each tenfold increase in I. This behaviour could not be explained satisfactorily with Humic Ion-Binding Model VI, a discrete-site/electrostatic model of cation binding by humic substances, parameterized with data from laboratory studies on isolated samples. More success was obtained by abandoning the impermeable-sphere electrostatic submodel used in Model VI, and instead assuming the peat to consist of aggregates with fixed internal volume, and with counterion accumulation described by the Donnan model, as proposed by Marinsky and colleagues. The fixed-volume Donnan model (Model VI-FD) could also approximately explain other reported results from acid-base titrations of peat, including the effects on the titrations of complexing cations (Al, Ca, Cu). Copper titrations of the Moor House sample were performed using an ion-selective electrode, with peat suspensions in the acid pH range, at two ionic strengths, and in the presence of Al and Ca. The measured concentrations of Cu2+ were in the range 10(-13)-10(-5) M. Model VI-FD provided reasonable fits of the experimental data, after optimization of the intrinsic binding constant for Cu, the optimized value being close to the default value derived previously from data referring to isolated humic substances. The optimized constants for Al and Ca, derived from their competition effects, were also close to their default values. Additional experiments were performed in which the centrifugation-depletion method was used to measure the binding of a cocktail of metals (Al, Ni, Cu, Zn, Cd, Eu, Pb) at a single pH. The model correctly predicted strong binding of Al, Cu, Eu and Pb, and weaker binding of Ni, Zn and Cd. For the strongly binding metals, the dissolved forms were calculated to be mainly due to complexes with dissolved humic matter, whereas the free ions (Ni2+, Zn2+, Cd2+) dominated for the weakly binding metals. Acid-washed soil appears to provide a valuable intermediate between isolated humic substances and untreated soil for the investigation of cation binding by natural organic matter in the natural environment.
Humic substances (HS) are the major components of the mixture of materials that comprise soil organic matter, and these substances, which are by far the most abundant organic materials in the environment, are themselves complicated mixtures of biologically transformed organic debris. However, it is likely that many of the solubilization properties of the mixtures arise from the presence of nonhumic components that are intimately associated with the HS and that cannot be separated effectively from these components. Separation and fractionation techniques are improving, and most of the instruments needed to advance awareness of the composition and aspects of structures are now in place. There is a need, however, to review the operational definitions that now apply and to put in place a classification system that will take into account origins and some compositional characteristics. The broad based definition of humin is especially unsatisfactory. This umbrella term covers a mixture of materials that are insoluble in aqueous systems and that contain nonhumic components such as long chain hydrocarbons, esters, acids, and even relatively polar structures of microbial origin, such as polysaccharides and glomalin, that can be associated with the nonpolar moieties and with soil minerals, as well as plant components that are highly resistant to decomposition. Advances in the humic sciences in recent times have been impressive, and the questioning of 'ingrained' theories and concepts is opening vistas through which we are seeing new concepts of size, shape, and association; the remarkable developments in nuclear magnetic resonance are also allowing better interpretations of compositions and of aspects of structures. From these advances will emerge a more fundamental understanding of HS functions in such important roles as the stabilization of soil aggregates, the binding of anthropogenic organic chemicals, and the sequestration of C from atmospheric CO2. The latter function is especially important at this time because we need to know why some soils sequester more C than others and why the qualities (or composition and structure) of HS in some soils are different from those in others.
The intrinsic basicity of 24 azoles (pyrazoles, indazoles, imidazoles, benzimidazoles) and 7-methylazaindole was determined by mass spectrometry techniques, ion cyclotron resonance (ICR) and/or chemical ionization (CI) in conjunction with tandem mass spectrometry (MS/MS). A reasonably good agreement (r2 = 0.967) is found between both methods (15 compounds). Thus, it is possible to use Ci/MS/MS to determine the intrinsic basicity of compounds not measurable by ICR for purity or volatility reasons. Some anomalies are interpreted in terms of entropy and steric effects. The basicity data are also discussed by using empirical models (sigma-alpha, sigma-R) and chelation and annelation effects.
We present an ab inito, quantum mechanical study of 18-crown-6 (18c6) and its interaction with the alkali metal cations Li[sup +], Na[sup +], K[sup +], Rb[sup +], and Cs[sup +]. Geometries, binding energies, and binding enthalpies are evaluated at the restricted Hartree-Fock (RHF) level using standard basis sets (3-21G and 6-31 + G*) and relativistic effective core potentials. Electron correlation effects are determined at the MP2 level, and wave function analysis is performed by the natural bond orbital (NBO) and associated methods. The affinity of 18c6 for the alkali metal cations is quite strong (50-100 kcal mol[sup [minus]1], depending on cation type), arising largely from the electrostatic (ionic) interaction of the cation with the nucleophilic ether backbone. Charge transfer (covalent bonding) contributions are somewhat less important, only 20-50% as strong as the electrostatic interaction. Agreement of the calculated binding enthalpies and experimentally determined quantities is rather poor. For example, the binding energy for K[sup +]/18c6 (-71.5 kcal mol[sup [minus]1]) is about 30 kcal mol[sup [minus]1] stronger than that determined by experiment, and it is not clear how to reconcile this difference. Our calculations clearly show that solvation effects strongly influence cation selectivity. 48 refs., 12 figs., 5 tabs.
Nonrelativistic and quasirelativistic energy-adjusted ab initio pseudopotentials are presented for element 105 (hahnium, Ha) together with corresponding energy-optimized valence basis sets. The method of energy adjustment of pseudopotentials is extended to a two-component formalism and to multiconfiguration wave functions. The accuracy of the pseudopotential scheme is demonstrated by a comparison of atomic valence-only results to corresponding all-electron data. Atomic multiconfiguration self-consistent field and multireference configuration interaction calculations for M and M[sup +] (M = Nb, Ta, Ha) are compared with available experimental data. Corresponding molecular calculations, which included spin-orbit coupling, have been performed for the low-lying states of HaO and are compared to the results from corresponding calculations of the lighter homologs NbO and TaO. 41 refs., 1 fig., 8 tabs.
Fulvic acid, isolated from the Suwannee River, Georgia, was assessed for its ability to bind Ca2+, Cd2+, Cu2+, Ni2+, and Zn2+ ions at pH 6 before and after extensive fractionation that was designed to reveal the nature of metal binding functional groups. The binding constant for Ca2+ ion had the greatest increase of all the ions in a metal binding fraction that was selected for intensive characterization for the purpose of building quantitative average model structures. The “metal binding” fraction was characterized by quantitative 13C NMR, 1H NMR, and FT−IR spectrometry and elemental, titrimetric, and molecular weight determinations. The characterization data revealed that carboxyl groups were clustered in short-chain aliphatic dibasic acid structures. The Ca2+ binding data suggested that ether-substituted oxysuccinic acid structures are good models for the metal binding sites at pH 6. Structural models were derived based upon oxidation and photolytic rearrangements of cutin, lignin, and tannin precursors. These structural models rich in substituted dibasic acid structures revealed polydentate binding sites with the potential for both inner-sphere and outer-sphere type binding. The majority of the fulvic acid molecule was involved with metal binding rather than a small substructural unit.
Noncovalent interactions play a dominant role in many forefront areas of modern chemistry, from materials design to molecular biology. A detailed understanding of the physical origin and scope of such interactions has become a major goal of physical organic chemistry. Compared to the more conventional interactions such as hydrogen bonds, ion pairs (salt bridges), and the hydrophobic interaction, the cation-π interaction has been relatively underappreciated. It is not a new effect-experimental support for a prominent interaction in the gas phase appeared more than 15 years ago, and the potential for such an interaction has always been evident from an electrostatic analysis of benzene.
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This critical examination of the kinetic method is carried out as part of a dialog-in-print with Peter Armentrout and László Drahos and Károly Vékey. We summarise the characteristics of the kinetic method and try to place it in the context of other thermokinetic methods of making thermochemical determinations, especially the threshold collision-induced dissociation method. We cover the approximations made in deriving the method and tabulate five forms of the method which have been used over the past 21 years. We show that many criticisms of the method apply to the simplest forms and, conversely, that a great deal of information can be obtained from those forms which do not assume that entropy effects cancel. A number of cases of apparent failure of the method are examined, including the alcohol/Li+ case described by Armentrout. We encourage continued use of each of the thermochemical methods but recommend that these uses be informed by knowledge of the subtleties of deriving thermochemical information from relative rate measurements. Copyright © 1999 John Wiley & Sons, Ltd.
In the context of the kinetic method, the effective temperature is defined as being equal to the real temperature of a population of cluster ions in thermal equilibrium, which would yield the same product ratio as that observed in the mass spectrometric experiment. The effective temperature is not a thermodynamic quantity and depends not only on the internal energy content but also on the experimental conditions. A very good correlation has been found between the effective temperature and the mean internal energy of ions dissociating in the time window of analysis, but not with the mean internal (or excess) energy of the whole ion population. Calculations suggest that assuming a high internal energy is unnecessary for the kinetic method to be accurate. Care should be taken, however, in evalulating entropy effects and to check that the cluster ions studied have the same (or a similar) effective temperature. Copyright © 1999 John Wiley & Sons, Ltd.
The kinetic method is examined from the point of view of a proponent of a complementary and sometimes competitive technique, threshold collision-induced dissociation. Limitations in the kinetic method and assumptions that have not been thoroughly examined in the literature are pointed out. A case study involving recent experiments in the author's laboratory is used to illlustrate the importance of including entropic effects in the data analysis, even for systems where the ligands are fairly similar. The author concludes by encouraging the use of the advanced kinetic methods outlined by Cooks et al. in the accompanying Commentary. Copyright © 1999 by John Wiley & Sons, Ltd.
Collision-induced dissociation (CID) of the Cs+ heterodimer adducts of the nitrate anion (NO3−) and a variety of substituted benzoates (XBenz−) [(XBenz−)(Cs+)(NO3−)]− produces essentially nitrate and benzoate ions. A plot of the natural logarithm of their intensity ratio, ln[I (NO3−)/I(XBenz−)], versus the calculated cesium cation affinity (DFT B3LYP) of the substituted benzoate ions (equivalent to the enthalpy of heterolytic dissociation of the salt) is reasonably linear. This suggests that the kinetic method can be used as a source of data on the intrinsic interaction between the anionic and the cationic moieties in a salt. Copyright © 2010 John Wiley & Sons, Ltd.
The e!ect of the addition of various humic substances on the adsorption of caesium on two mineral clays has been studied. All measurements were carried out in dilute suspension under controlled conditions of temperature and ionic strength. Only a small proportion of the humic substance was adsorbed on the clays ((10%). In general, the a$nity of the clay}humic complexes for caesium was less than that of the bare clay. The decrease was greater for illite than for montmorillonite, and greatest at trace concentrations of caesium and increased with increasing concentration of each humic substance. However, no correlation was found between the amount of humic substance adsorbed and the decrease in Cs adsorption when all complexes were considered. Neither size nor the origin of the humic substances could explain the extent of the adsorption decrease. Since neither steric hindrance nor decrease in the number of adsorp-tion sites was the driving force behind this phenomenon, it is hypothesized that the a$nity of the clay surface is modi"ed by the organic macromolecules. The highly selective frayed edge sites of illite are particularly sensitive to the adsorption of polyanions because of their proximity to anion adsorption sites. The observed decrease in Cs adsorption may contribute to the unexpectedly high bioavailability of Cs in organic soils.
A small fraction of carboxylic acid functional groups in humic substances are exceptionally acidic with pKa values as low as 0.5. A review of acid-group theory eliminated most models and explanations for these exceptionally acidic carboxyl groups. These acidic carboxyl groups in Suwannee River fulvic acid were enriched by a 2-stage fractionation process and the fractions were characterized by elemental, molecular-weight, and titrimetric analyses, and by infrared and 13C- and 1H-nuclear magnetic resonance spectrometry. An average structural model of the most acidic fraction derived from the characterization data indicated a high density of carboxyl groups clustered on oxygen-heterocycle alicyclic rings. Intramolecular H-bonding between adjacent carboxyl groups in these ring structures enhanced stabilization of the carboxylate anion which results in low pKa1 values. The standard, tetrahydrofuran tetracarboxylic acid, was shown to have similar acidity characteristics to the highly acidic fulvic acid fraction. The end products of 3 known diagenetic pathways for the formation of humic substances were shown to result in carboxyl groups clustered on oxygen-heterocycle alicyclic rings.
The relatively small diffuse function-augmented basis set, 3-21+G, is shown to describe anion geometries and proton affinities adequately. The diffuse sp orbital exponents are recommended for general use to augment larger basis sets.
The Fukushima Dai-ichi nuclear power plant accident in Japan, triggered by a big earthquake and the resulting tsunami on 11 March 2011, caused a substantial release of radiocesium ((137)Cs and (134)Cs) and a subsequent contamination of soils in a range of terrestrial ecosystems. Identifying factors and processes affecting radiocesium retention in these soils is essential to predict how the deposited radiocesium will migrate through the soil profile and to other biological components. We investigated vertical distributions of radiocesium and physicochemical properties in soils (to 20 cm depth) at 15 locations under different land-use types (croplands, grasslands, and forests) within a 2 km × 2 km mesh area in Fukushima city. The total (137)Cs inventory deposited onto and into soil was similar (58.4±9.6 kBq m(-2)) between the three different land-use types. However, aboveground litter layer at the forest sites and herbaceous vegetation at the non-forested sites contributed differently to the total (137)Cs inventory. At the forest sites, 50-91% of the total inventory was observed in the litter layer. The aboveground vegetation contribution was in contrast smaller (<35%) at the other sites. Another remarkable difference was found in vertical distribution of (137)Cs in mineral soil layers; (137)Cs penetrated deeper in the forest soil profiles than in the non-forested soil profiles. We quantified (137)Cs retention at surface soil layers, and showed that higher (137)Cs retention can be explained in part by larger amounts of silt- and clay-sized particles in the layers. More importantly, the (137)Cs retention highly and negatively correlated with soil organic carbon content divided by clay content across all land-use types. The results suggest that organic matter inhibits strong adsorption of (137)Cs on clay minerals in surface soil layers, and as a result affects the vertical distribution and thus the mobility of (137)Cs in soil, particularly in the forest ecosystems.
Organic acids, such as malate, citrate and oxalate, have been proposed to be involved in many processes operating in the rhizosphere, including nutrient acquisition and metal detoxification, alleviation of anaerobic stress in roots, mineral weathering and pathogen attraction. A full assessment of their role in these processes, however, cannot be determined unless the exact mechanisms of plant organic acid release and the fate of these compounds in the soil are more fully understood. This review therefore includes information on organic acid levels in plants (concentrations, compartmentalisation, spatial aspects, synthesis), plant efflux (passive versus active transport, theoretical versus experimental considerations), soil reactions (soil solution concentrations, sorption) and microbial considerations (mineralization). In summary, the release of organic acids from roots can operate by multiple mechanisms in response to a number of well-defined environmental stresses (e.g., Al, P and Fe stress, anoxia): These responses, however, are highly stress- and plant-species specific. In addition, this review indicates that the sorption of organic acids to the mineral phase and mineralisation by the soil's microbial biomass are critical to determining the effectiveness of organic acids in most rhizosphere processes.
The radioactivity of the Opa river — irrigated farmlands in the south western Nigeria was determined using an HpGe based,
low-level passive gamma-counting system. With the exception of two isotopes, the main radionuclides analysed in the sample
were the progenies of238U and232Th. The other two isotopes were the naturally occurring40K and the anthropogenic137Cs. The result obtained showed elevated levels of radioactivity from all detected radionuclides compared to the published
data for this area. Enhanced levels of naturally occurring radionuclides is attributed to the use of phosphatic fertilizers
for dry season vegetable cultivation along this river banks. The presence of the fission product137Cs could be traced to the fallouts occasioned by the various French nuclear tests in the Sahara desert, and probably, some
effect of the more recent nuclear reactor accident at Chernobyl in 1986.
Highly organic soils, and in particular ombrotrophic bogs, have been often used to reconstruct climate changes and heavy metal
contaminations. Ombrotrophic peat bogs, in fact, are domed peatlands in which the surface layers are hydrologically isolated
from the influence of local groundwaters and surface waters, and are supplied only by atmospheric depositions. In the present
work, the attention of Authors has been focused on Pb, Cu, and Zn, coming mainly from anthropogenic activities, and 137Cs, released mostly during the Chernobyl disaster. Practically, an undisturbed peat profile was cored in 2005 from a Swiss
ombrotrophic bog and analysed using energy-dispersive miniprobe multielement analyzer X-ray fluorescence and Low Background
γ-ray spectrometry in order to investigate and quantify the impact of human activities (e.g., industry, traffic, combustion
of fossil fuels, “environmental disasters”) in causing Pb, Cu, Zn, and 137Cs contaminations during the centuries. Obtained data show that highly organic soils in general, and ombrotrophic bogs in
particular, reflect the anthropogenic inputs in heavy metal and radionuclide contaminations. In fact, these environments allowed
to follow the depositional history of Pb, Cu, and Zn, both underlining a general increasing of their production since the
Industrial Revolution, and remarking past single impacting events such as the introduction of leaded gasoline and of particular
agricultural practices. Further, although 137Cs showed a main peak corresponding to the Chernobyl disaster, confirming the role of bogs as archive of human activity, data
revealed a certain mobility of this radionuclide along the profile. Thus, highly organic soils can be considered as both “witness”
of the impact of human activity during centuries and indicator of the health of our planet.
The functional characteristics of forest soils in the mountainous regions in Bulgaria were assessed in order to obtain a better understanding of cesium distribution in soil. The aim of this paper is to describe the small-scale spatial variability of Cs-137 contamination in forest floor and surface soil layers in relation to regional and local characteristics. The mountainous regions of Bulgaria were strongly and inhomogeneously contaminated with cesium-137 due to the Chernobyl accident in 1986. The study confirmed that the cesium in forest soils from two mountainous regions of Bulgaria, SW Rila Mountain and Central Balkan, is located in the forest floor and upper 0–5 cm of soil. In a few cases from Central Balkan the maximum activities are found at a soil depth 5–10 cm. The measured values of cesium activity concentration in Aoh in Rila Mountain region are between 287.9 and 827.1 Bq kg− 1. Greater variations in cesium activity concentration in forest floor are determined for the plots from Central Balkan, where the measured values in Aof are between 85.7 and 2543 Bq kg− 1. The contamination density of Cs-137 in fine soil (< 1 mm) from Rila varies from 0.6 to 6.0 kBq m− 2 while in the Central Balkan plots it is between 1.2 and 19.6 kBq m− 2. The forest floor remains the main reservoir for cesium even years after pollution. The profile distribution of Cs-137 in soil systems shows a tendency of decrease toward deeper layers. The mountainous ecosystems with different types of vegetation were compared on the basis of estimated factor of accumulation (FA). The FA for conifers in Rila Mountain is from 0.28 to 0.69 and in the Central Balkans the FA is from 0.20 to 0.61. The data showed that the spatial distribution of Cs-137 in soil system depends on type of vegetation, humus type and altitude. Due to their low clay content and the high content of organic matter, the mountain forest soils can be considered an excellent ecosystem in which to study the mobility and behaviour of Cs-137 and its transfer into the soil-plant system. Due to the high levels of radiocesium contamination within the mountainous regions of the Central Balkan and the characteristics of soils, the highland mountain herbaceous ecosystems located in this region, in the authors’ opinion, could be considered as risk zones to easier soil-to-plant transfer of cesium.
Standard humic substances (HS) were stored in 13C-labelled methanol, ethanol, 2-propanol and d3-methanol to investigate whether they underwent self-esterification with the solvents or not. Data from stable carbon isotope analysis, 13C NMR spectroscopy and electrospray ionisation mass spectrometry (ESI-MS) showed that significant self-esterification of carboxyl groups began immediately after dissolution. The major implication is that data collected in previous studies using these solvents in conjunction with HS are likely to be compromised. Self-esterification was minimised by varying parameters such as % water, temperature, concentration, storage time and buffer. Solvent reactivity was found to be: ethanol > 2-propanol > methanol. The study proposes preliminary guidelines for the preparation and storage of HS and their analysis by ESI-MS. The primary recommendation is to avoid the use of these solvents and use alternatives such as acetonitrile and water.
Cesium-137 derived from the explosion of the Chernobyl reactor in 1986 was preserved in anoxic sediments from a coastal environment in southern Rhode Island. Although the radioactive plume was detected in surface air samples at several locations in the United States, this is the first known record of a Chernobyl 137Cs peak in sediments from North America. The inventory of Chernobyl 137Cs that was preserved in the Pettaquamscutt River is small compared to European counterparts and should only be detectable for the next 15–20 yr. However, the presence of two 137Cs peaks (1963 and 1987) identifies a well-dated segment of the sediment column that could be exploited in understanding the decomposition and preservation of terrestrial and aquatic organic matter. Different methods for calculating the 210Pb chronology were also evaluated in this study and checked against independent varve counting. The end result is a detailed chronology of a site well suited for reconstruction of historical records of environmental change.
Despite the remarkable thermochemical accuracy of Kohn–Sham density-functional theories with gradient corrections for exchange-correlation [see, for example, A. D. Becke, J. Chem. Phys. 96, 2155 (1992)], we believe that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional containing local-spin-density, gradient, and exact-exchange terms is tested on 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total atomic energies of first- and second-row systems. This functional performs significantly better than previous functionals with gradient corrections only, and fits experimental atomization energies with an impressively small average absolute deviation of 2.4 kcal/mol.
Plant roots serve a multitude of functions in the plant including anchorage, provision of nutrients and water, and production of exudates with growth regulatory properties. The root–soil interface, or rhizosphere, is the site of greatest activity within the soil matrix. Within this matrix, roots affect soil structure, aeration and biological activity as they are the major source of organic inputs into the rhizosphere, and are also responsible for depletion of large supplies of inorganic compounds. Roots are very complicated morphologically and physiologically, and their metabolites are often released in large quantities into the soil rhizosphere from living root hairs or fibrous root systems. Root exudates containing root-specific metabolites have critical ecological impacts on soil macro and microbiota as well as on the whole plant itself. Through the exudation of a wide variety of compounds, roots impact the soil microbial community in their immediate vicinity, influence resistance to pests, support beneficial symbioses, alter the chemical and physical properties of the soil, and inhibit the growth of competing plant species. In this review, we outline recent research on root exudation and the role of allelochemicals in the rhizosphere by studying the case of three plants that have been shown to produce allelopathic root exudates: black walnut, wheat and sorghum