Addition Of Ln Research Articles

Relative efficacy and stability of biological and synthetic nitrification inhibitors in a highly nitrifying soil: Evidence of apparent nitrification inhibition by linoleic acid and linolenic acid

AbstractBiological nitrification inhibition is a plant‐mediated rhizosphere process where natural nitrification inhibitors can be produced and released by roots to suppress nitrifier activity in soil. Nitrification is one of the critical soil processes in the nitrogen (N) cycle, but unrestricted and rapid nitrification in agricultural systems can result in major losses of N from the plant–soil system (i.e., by NO3− leaching and gaseous N emissions). In this study, we explored the potential efficacy of biological nitrification inhibitors (linoleic acid [LA] and linolenic acid [LN]) and a proven efficient synthetic (dicyandiamide [DCD]) nitrification inhibitor on N dynamics, nitrous oxide (N2O) and carbon dioxide (CO2) emissions in a highly nitrifying soil. 14C‐labelled LA, LN and DCD mineralization was determined in a parallel experiment to explore the fate of inhibitors after application. We found that LA and LN had no effect on soil NH4+ concentrations, but significantly decreased NO3− concentrations. Soil that received DCD had lower NO3− and higher NH4+ concentrations than the control (soil without nitrification inhibitors). LA and LN increased the cumulative N2O and CO2 emissions when they were applied at high concentrations (635 or 1,270 mg kg−1 dry soil). LA and LN had a much greater mineralization rate than that of DCD: 47–56%, 37–61% and 2.7–5.5%, respectively, after 38 days incubation. We conclude that in contrast to the direct inhibition of nitrification caused by DCD, addition of LA and LN may cause apparent nitrification inhibition by promoting microbial immobilization of soil NH4+ and/or NO3−. Future studies on nitrification inhibitors need to clearly differentiate between the direct and indirect effects that result from addition of these compounds to soil.Highlights The efficacy and stability of nitrification inhibitors in a highly nitrifying soil were explored. This study supports efforts to mitigate N losses and improve nitrogen use efficiency of inputs. Addition of LA, LN and DCD can decrease NO3− concentration, but their modes of action may be different. The apparent effect of LA and LN on soil NO3− concentration could be indirect.

Improved energy storage properties of La0.33NbO3 modified 0.94Bi0.5Na0.5TiO3-0.06BaTiO3 ceramic system

(1−x)[0.94Bi0.5Na0.5TiO3 – 0.06BaTiO3]−xLa0.33NbO3 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) (BNBT-LN) bulk lead-free relaxor ferroelectric ceramics were synthesized via solid-state sintering method. Phase, microstructure and energy storage properties were determined. The X-ray diffraction (XRD) revealed a single perovskite phase for compositions of x ≤ 0.02, while the second phase of Bi2Ti2O7 along with the parent phase for x ≥ 0.04. Dense microstructure with a decrease in grain size has been achieved via LN doping. The addition of LN decreased the remnant polarization (Pr), and coercive field (Ec), while increased the difference between the maximum polarization (Pmax) and remnant polarization (Pr). The high energy-storage density of 2.96 J/cm 3 and high recoverable energy density of 1.66 J/cm3 at a breakdown electric field of 214 kV/cm were achieved for the composition of x = 0.02 with good temperature stability satisfying the condition of Δer /e r200 °C ≤ ± 15% in a working temperature range of 70 °C to 400 °C. Similarly, a less discharge time of < 4 µs achieved in this study for x = 0.02. These results demonstrate that this material may be a good candidate material for power pulsed applications.

Functionalized Trigonal Lanthanide Complexes: A New Family of 4f Single-Ion Magnets.

We report the synthesis, characterization, and magnetic properties of eight neutral functionalized trigonal lanthanide coordination complexes LnL with Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5), Tm (6), Yb (7), Lu (8). These were prepared through a one-pot synthesis where, first, the ligand H3L was synthesized in situ through a Schiff base reaction of tris(2-aminoethyl)amine with 2,6-diformyl-p-cresol. Following addition of Ln(OTf)3·xH2O and base, LnL was obtained. Powder X-ray diffraction confirms that all complexes are isostructural. LnL contain pendant, noncoordinating carbonyl functions that are reactive and represent direct anchoring points to appropriately functionalized surfaces. Furthermore, these reactive carbonyl functions can be used to postfunctionalize LnL: for example, with aromatic π systems. We present herein the Schiff base condensation of 7 with benzylamine to yield 9 as well as the characterization and magnetic properties of 9. Our study establishes LnL as a truly versatile module for the surface deposition of Ln-based single-ion magnets.

Understanding the activation mechanism of Pb2+ ion in benzohydroxamic acid flotation of spodumene: Experimental findings and DFT simulations

In recent years, benzohydroxamic acid (BHA) has been widely used as a selective collector in the flotation of oxide minerals such as scheelite, wolframite, cassiterite and ilmenite despite its moderate collecting ability. Lead nitrate (Pb(NO3)2, LN) is a commonly used activator for improving BHA flotation. According to the classical activation theory, the pre-adsorbed Pb2+ ion can increase the number of active site on oxide mineral surface, thus increasing the subsequent adsorption amount of BHA collector. In this study, BHA and LN were used, for the first time, in the flotation of spodumene, a valuable silicate and major source mineral for lithium battery materials. Interestingly, the adsorption test results show that the adsorption amount of BHA on spodumene surface was the same whether LN was added or not, while the micro-flotation test results show that the addition of LN helped increase the spodumene recovery from 0 to 80% using 120 mg/L BHA at pH 8. These results seem to be contradictory to the classical activation theory, yet by using density functional theory-based first-principle calculations, X-ray photoelectron spectroscopy and atomic force microscopy theoretically and experimentally, their underlying mechanism is therefore revealed. Those results show that in the absence of LN, a “flat” adsorption mode with the benzene ring of BHA parallel to the spodumene surface, is more inclined to a monodentate mode between O2− ion (attached to N) of BHA and surface Al3+ ion, leading to an adsorption energy of −113 kJ/mol. While with the presence of LN, a “vertical” adsorption mode with the benzene ring perpendicular to the spodumene surface, is favored in a bidentate mode between two O2− ions of BHA and Pb2+ ion of pre-adsorbed solvated Pb(OH)+ complex, leading to a much higher adsorption energy of −270 kJ/mol. Based on coordination chemistry analysis, differences in the adsorption mode and energy of BHA on Pb2+-activated and unactivated spodumene surfaces can be explained by differences in coordination number and bond dissociation energy. This study will provide valuable insights into the activation of Pb2+ ion in BHA flotation of valuable silicate minerals, and help to enrich understanding of activation mechanisms of metal ions in anionic collector flotation of minerals.

Insertion of Trivalent Lanthanides into Uranyl Vanadate Layers and Frameworks.

Two new uranyl vanadates have been prepared from hydrothermal reactions and structurally characterized by single-crystal X-ray diffraction. The structure of (H3O)UO2VO4 (UVO-1) consists of anionic layers containing UO2(2+) pentagonal bipyramids coordinated by edge-sharing VO5 square pyramids, with the charge balanced by interlaminar H3O(+) cations. Vanadium in (UO2)3(VO4)2(H2O)3 (UVO-2) exists as monomeric VO4 tetrahedra coordinating to UO2(2+) pentagonal bipyramids, forming a 3D uranyl(VI) vanadate framework. Similar reactions with the addition of Ln(NO3)3 (Ln = Nd, Eu) afford the three heterobimetallic lanthanide uranyl vanadate frameworks Nd(UO2)3(VO4)3(H2O)11 (NdUVO-1), Eu(UO2)3(VO4)3(H2O)10 (EuUVO-1), and Eu2(UO2)12(VO4)10(H2O)24 (EuUVO-2). In NdUVO-1 and EuUVO-1, Ln(3+) cations are inserted into the interlayer space of UVO-1 substituting for H3O(+) and further bridging adjacent layers into 3D frameworks. Similarly, EuUVO-2 adopts the same sheet topology as UVO-2, with Eu(3+) ions replacing some of the interlayer uranyl ions in UVO-2. Our work has demonstrated that uranyl vanadate extended structures are excellent hosts for further incorporation of trivalent lanthanide/actinide cations and has provided a new way to create new heterobimetallic 4f-5f and 5f-5f compounds.

Phase transition behavior and electrical properties of lead-free (Bi0.5K0.5)TiO3–LiNbO3 relaxor ferroelectric ceramics

(1−x)(Bi0.5K0.5)TiO3–xLiNbO3 ((1−x)BKT–xLN) lead-free relaxor ferroelectric ceramics were prepared by a conventional solid-state route and their phase transition behavior and the corresponding electrical properties were investigated. A morphotropic phase boundary separating rhombohedral and tetragonal phases was identified in the composition range of 0.015<x<0.03, where the improved electrical properties of piezoelectric constant d33=75pC/N and electromechanical coupling factor kp=0.18 were obtained. Moreover, all samples show typical relaxor behavior characterized by the presence of diffuse phase transition and frequency dispersion. It was found that the dielectric relaxation behavior of BKT ceramics can be obviously enhanced with the addition of LN. In addition, the effect of the LN addition on the ferroelectric properties was also investigated by measuring polarization versus electric field hysteresis loops.

A Double Addition of LnH to a Carbon–Carbon Triple Bond and Competitive Oxidation of Ytterbium(II) and Hydrido Centers

Addition of two Ln-H bonds of an Yb(II) hydrido complex supported by bulky amidinate ligand to a C≡C bond lead to the formation of 1,2-dianionic bibenzyl fragment. Both Yb(II) and hydrido centers are oxidized under the reaction conditions. The resulting Yb(II)-η(6) -arene interaction is surprisingly robust: the arene cannot be replaced from the metal coordination sphere when treated with Lewis bases.

A Double Addition of LnH to a Carbon–Carbon Triple Bond and Competitive Oxidation of Ytterbium(II) and Hydrido Centers

A Double Addition of LnH to a Carbon–Carbon Triple Bond and Competitive Oxidation of Ytterbium(II) and Hydrido Centers

Microstructure and Properties of High-Temperature Materials (1−x) Na0.5Bi2.5Nb2O9-xLiNbO3

Bismuth layer-structured ferroelectric ceramics of (1−x)Na0.5Bi2.5Nb2O9–xLiNbO3 (NBN–LN, 0≤x≤0.2) were synthesized by a traditional solid-state reaction. The effects of LN addition on the microstructure and electrical properties of ceramics were studied carefully. It was found that the ceramics with x≤0.10 have a bismuth oxide layered structure. With the increasing of LN addition, the mechanical quality factor Qm firstly increases, and then decreases with a maximum value of 4820 at x=0.02. The Curie temperature Tc increases gradually and the electrical properties of NBN-based ceramics are improved significantly by the addition of LN. The piezoelectric constant d33, dielectric loss tan δ, Curie temperature Tc, and remanent polarization Pr of 0.90Na0.5Bi2.5Nb2O9–0.10LiNbO3 ceramics were found to be 21 pC/N, 0.16%, 789°C, and 7.37 μC/cm2, respectively. Thermal annealing and aging studies indicate that the NBN–LN system possesses stable piezoelectric properties, demonstrating that the NBN–LN ceramics are the promising candidates for high-temperature applications.

Ru(bipy)3]2+ and [Os(bipy)3]2+ chromophores as sensitisers for near-infrared luminescence from Yb(iii) and Nd(iii) in d/f dyads: contributions from Förster, Dexter, and redox-based energy-transfer mechanisms

The complexes and contain [M(bipy)(3)](2+) chromophores with a pendant aza-18-crown-6 macrocycle for binding of lanthanide(iii) ions. The photophysical properties of the adducts . and ., prepared by addition of excess Ln(NO(3))(3) (Ln = Nd, Yb) to solutions of and in MeCN, were examined using time-resolved and steady-state luminescence methods. Whereas does not act as an energy-donor to Yb(iii), it will transfer energy to (and generate sensitised near-infrared luminescence from) Nd(iii) with a Ru(ii)-->Nd(iii) energy-transfer rate constant of 6.8 x 10(6) s(-1). In contrast, is quenched by both Yb(iii) and Nd(iii), but with faster energy-transfer to Yb(iii) (2.6 x 10(7) s(-1)) than to Nd(iii) (1.4 x 10(7) s(-1)). Thus d --> f energy transfer is in both cases faster for Os(ii) than for Ru(ii), but the relative ability of Nd(iii) and Yb(iii) to act as energy-acceptors is inverted from . to .. Reasons for this are discussed with reference to contributions from the Förster and Dexter mechanism for energy-transfer in . and ., using calculated spectroscopic overlap integrals coupled with molecular modelling to estimate inter-chromophore separations. The particular effectiveness of Os(ii) --> Yb(iii) energy-transfer in . is explained in terms of the Horrocks redox mechanism involving an initial *Os(ii) --> Yb(iii) photoinduced electron transfer step generating an Os(iii)/Yb(ii) state, which is shown to be marginally favourable for ., but not for . in which the [Ru(bipy)(3)](2+) unit is a poorer excited-state electron-donor by about 0.1 eV.

Photocatalytic Water Splitting into H2 and O2 over Titanate Pyrochlores Ln2Ti2O7 (Ln = Lanthanoid: Eu–Lu)

Abstract A series of titanate pyrochlore Ln2Ti2O7 (Ln = Eu–Lu) was prepared by a polymerized complex method and evaluated as a photocatalyst for water splitting reaction. All the Ln2Ti2O7, except for Tb2Ti2O7, demonstrated evolution of H2 and O2 in a stoichiometric ratio from pure water under UV-light irradiation. The photocatalytic activities of the Ln2Ti2O7 were significantly enhanced by the addition of excess Ln (5%) in the preparation procedure. As for the Ln2Ti2O7 containing small Ln3+ (Ln = Dy–Lu), the enhanced photocatalytic activity can be explained by the suppression of impurity phase formation, rutile titanium oxide (TiO2), which formed in the stoichiometric preparation at high temperature. It was also found that the addition of excess Ln increased the surface area of these materials, which certainly contributed to the enhanced photocatalytic activity. In the case of Gd2Ti2O7, the photocatalytic activity was remarkably improved by the addition of excess Gd, in spite of the fact that no impurity phase formed even in the stoichiometric preparation. Scanning electron microscopy (SEM) and pore size distribution analysis revealed that the addition of excess amount of Gd made the Gd2Ti2O7 material porous, which is undoubtedly one of the major factors enhancing the photocatalytic activity.

A nonparametric method for the measurement of size diversity with emphasis on data standardization

The most suitable method for estimation of size diversity is investigated. Size diversity is computed on the basis of the Shannon diversity expression adapted for continuous variables, such as size. It takes the form of an integral involving the probability density function (pdf) of the size of the individuals. Different approaches for the estimation of pdf are compared: parametric methods, assuming that data come from a determinate family of pdfs, and nonparametric methods, where pdf is estimated using some kind of local evaluation. Exponential, generalized Pareto, normal, and log‐normal distributions have been used to generate simulated samples using estimated parameters from real samples. Nonparametric methods include discrete computation of data histograms based on size intervals and continuous kernel estimation of pdf. Kernel approach gives accurate estimation of size diversity, whilst parametric methods are only useful when the reference distribution have similar shape to the real one. Special attention is given for data standardization. The division of data by the sample geometric mean is proposed as the most suitable standardization method, which shows additional advantages: the same size diversity value is obtained when using original size or log‐transformed data, and size measurements with different dimensionality (longitudes, areas, volumes or biomasses) may be immediately compared with the simple addition of ln k where k is the dimensionality (1, 2, or 3, respectively). Thus, the kernel estimation, after data standardization by division of sample geometric mean, arises as the most reliable and generalizable method of size diversity evaluation.

Stuffed rare earth pyrochlore solid solutions

Synthesis and crystal structures are described for the compounds Ln 2(Ti 2− xLn x )O 7− x /2, where Ln=Tb, Dy, Ho, Er, Tm, Yb, Lu, and x ranges from 0 to 0.67. Rietveld refinements of X-ray powder diffraction data indicate that in the Tb and Dy titanate pyrochlores, the extra Ln 3+ cations mix mainly on the Ti 4+ site with little disorder on the original Ln 3+ site. For the smaller rare earths (Ho–Lu), stuffing additional lanthanide ions results in a pyrochlore to defect fluorite transition, where the Ln 3+ and Ti 4+ ions become completely randomized at the maximum ( x=0.67). Initial magnetic characterization for the fully stuffed x=0.67 samples for Ln=Tb–Yb shows no long range ordering down to 2 K, and only partial saturation of the full expected magnetic moment under applied fields up to 5 T. In all of these Ln–Ti–O pyrochlores, the addition of magnetic Ln 3+ in place of non-magnetic Ti 4+ adds edge sharing tetrahedral spin interactions to a normally corner sharing tetrahedral network of spins. The increase in spin connectivity in this family of solid solutions represents a new avenue for investigating geometrical magnetic frustration in the rare earth titanate pyrochlores.

Structure-based description of a step-by-step synthesis of homo- and heterodinuclear (4f, 4f ') lanthanide complexes.

The stepwise course of the synthesis of homo- (4f, 4f) and heterodilanthanide (4f, 4f ') complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, the tripodal ligand H(3)L is reacted with Ln(NO(3))(3) x 5H(2)O to give a complex (H(3)L)Ln(NO(3))(3) in which the ligand does exist in a zwitterionic form. This unexpected feature has been definitely supported by a structural determination performed on a closely related complex (HL')(3)Ln(NO(3))(3) (1). These species are fairly stable and may be isolated. In basic medium, (H(3)L)Ln(NO(3))(3) is deprotonated to yield a neutral LLn complex crystallized as LLnNaClO(4) (2), the lanthanide ion being linked to the inner N(4)O(3) coordination site of the ligand. Finally, addition of Ln'(NO(3))(3) x 5H(2)O (Ln' being similar or different from Ln) to the LLn complex yields the desired homo- or heterodinuclear LLnLn'(NO(3))(3) complex 3, where the Ln' ion is coordinated to the outer O(3)O(3) coordination site of the tripodal ligand. Complex 1 (Ln = La) crystallizes in the triclinic space group P1 (No. 2): a = 11.1883(7) A, b = 11.8993(9) A, c = 16.4197(10) A, alpha = 81.900 (6) degrees, beta = 79.406(5) degrees, gamma = 79.470(6) degrees, V = 2099.5(2) A(3), Z = 2. Complex 2 (Ln = Eu) crystallizes in the monoclinic space group P2(1)/n (No. 14): a = 13.6333(13) A, b = 15.3799(12) A, c = 17.1473(13) A, beta = 111.283(10) degrees, V = 3350.2(5) A(3), Z = 4. Complex 3 (Ln = Ln' = Dy) crystallizes in the trigonal space group R3 (No. 148) with a = b = 23.847(3) A, c = 42.982(2) A, V = 21168(4) A(3), Z = 18. Complex 3 possesses a Dy(O(phenoxo))(3)Dy core, and a nitrato anion has been replaced by a eta(2)-chelated o-vanillin anion. We did not succeed in obtaining crystals of any of the heterodinuclear LLnLn'(NO(3))(3) entities, but their existence was unambiguously confirmed by positive fast atom bombardment mass spectrometry experiments.

1-Octene Hydrosilylation Catalyzed by Lanthanide and Yttrium Hydrides and Hydrocarbyls: A Mechanistic Study and the Role of Catalyst Association

Dimeric lanthanide (Tb, Yb, Lu) and yttrium hydrides, {Cp‘2Ln(μ-H)}2, where Cp‘ = t-BuC5H4, and hydrocarbyls {Cp‘2Ln(μ-Me)}2, as well as compounds with different bridging, Cp‘2Ln(μ-H)(μ-Me)LnCp‘2, are efficient and selective catalysts of 1-octene hydrosilylation. Binuclear complexes with Ln(μ-H)2Ln and Ln(μ-H)(μ-Alkyl)Ln bridging fragments were found to be the key intermediates in 1-octene hydrosilylation catalyzed by both the hydrides {Cp‘2Ln(μ-H)}2 (Ln = Y, Tb, Yb, Lu) and the mixed compounds Cp‘2Ln(μ-H)(μ-Me)LnCp‘2 (Ln = Y, Lu) in benzene at 75 °C. Therefore, in this case, the dissociation of the starting dimeric organolanthanide into monomeric species is not required for the catalytic reaction to proceed. Under the conditions employed, the rate law for the hydrosilylation of 1-octene with PhMeSiH2 is VHS ∼ [lanthanide]1[olefin]1[silane]0, suggesting rapid hydride transfer from silane to Ln and the rate-limiting addition of Ln−H to olefin. The hydrosilylation of 1-octene with n-Bu2SiH2 is accompanied by olefin dimerization. In the presence of Ph3SiH, Ph2MeSiH, PhMe2SiH, Et3SiH, and Et3GeH, only the dimerization of 1-octene was observed. Alternatively, the lanthanide and yttrium hydrocarbyls {Cp‘2Ln(μ-Me)}2 (Ln = Y, Tb, Yb, Lu) exhibit higher catalytic activity even at room temperature.The initial rate of the 1-octene hydrosilylation with PhMeSiH2 was found to be V0 ∼ [lanthanide]1/2[olefin]1[silane]0. In this case, the hydrosilylation seems to involve the formation of highly active monomeric species Cp‘2LnH. After several minutes, the hydrosilylation rate sharply decreased because of association of the catalyst.

Ln(III)-Catalyzed Cleavage of Phosphate-Functionalized Synthetic Lipids: Real Time Monitoring of Vesicle Decapsulation

Double-chain zwitterionic phosphate lipids (1a,b) have been synthesized. Upon their hydrolysis, two single-chain surfactants, soluble in water, are produced. The presence in the cationic counterpart of a p-nitrophenol subunit allows one to monitor spectrophotometrically the cleavage process. By sonication, lipids 1 form stable vesicles which are in the fluid state in the temperature interval explored (5−55 °C) and are too leaky to trap the fluorescent dye 4(5)-carboxyfluoresceine (CF). In the case of 1a, addition of at least 10% cholesterol increases the packing of the lipids making the vesicles less permeable to CF although at up to 40% additive the membrane remains in its fluid state. Holovesicular compounds 1 are hydrolytically very stable at pH 7, but the addition of different Ln(III) ions (Eu, Tm, Tb) efficiently catalyzes the hydrolytic cleavage (t1/2 ca. 45 min at 25 °C with 1 mM Eu(III)), which follows a regular monoexponential kinetic process. In the case of the vesicular preparation of 1a containing cholesterol, the kinetic profile is more complicated and can be divided into three regions: a first monoexponential part accounting for the cleavage of ca. 30% of the lipids residing in the external leaflet of the membrane; a second part in which all lipids start to be exposed to the metal ion; a third part, again monoexponential, in which all the remaining lipids are cleaved. Experiments with trapped CF show that in correspondence with the time in which the metal ions start to interact with all lipids, the rate of dye release increases although the aggregate maintains its vesicular structure. Analysis of the data strongly suggests that in the hydrolytic process the exposure of all lipids to the action of the metal ions is the result of both permeation and increased flip-flop of the phosphate-functionalized lipids. This would indicate that the hydrolytic process affects lipid mobility more than the permeability of the bilayer.

Oxidative fluorescence quenching of zinc tetraphenylporphyrin (ZnTPP) by trivalent lanthanide ions in several solvents: Role of lanthanide-induced singlet–triplet crossing

The fluorescence emission arising from the S 1 -state of zinc tetraphenylporphyrin (ZnTPP) is quenched by trivalent lanthanide ions in different solvents. The quenching process involves several types of interactions. The paramagnetic Ln 3+-ions enhance the spin-orbit coupling of ZnTPP facilitating singlet–triplet crossing or induced system crossing ( k ind SC). Values of k ind SC measured for different Ln 3+-ions exhibit a fair correlation with the number of unpaired f-electrons in the Ln 3+-ions used. Induced system crossing reaches a limiting value at a critical [Ln 3+], which is of the order of (2–5)×10 −3 M, and it does not increase upon further addition of Ln 3+-ions. Contribution of electronic excitation energy transfer from 1 ZnTPP* to Ln 3+-ions is limited to Pr 3+, Ho 3+, Nd 3+, Er 3+ and Tm 3+ ions only, due to very unfavorable spectral overlap with remaining Ln 3+-ions. On the other hand, electron transfer from 1 ZnTPP* (and possibly 3 ZnTPP* ) to Ln 3+-ions, which is thermodynamically allowed for several Ln 3+-ions depending upon the solvent used, plays a significant role in the quenching of 1 ZnTPP* (S 1) in CH 3CN, a limited role in DMF and a negligible role in 2-propanol, in spite of favorable Δ G 0 el.tr. values in the latter. Values of k ind SC and ( k ET+ k el.tr.) in CH 3CN range from 1.6×10 7 s −1 (Tm 3+) to 7.0×10 7 s −1 (Gd 3+) and 1.2×10 10 M −1 s −1 (Eu 3+) to nearly zero (Gd 3+), respectively. Corresponding values in DMF are lower.

Conducting airway gas exchange: diffusion-related differences in inert gas elimination.

We studied CO2 and inert gas elimination in the isolated in situ trachea as a model of conducting airway gas exchange. Six inert gases with various solubilities and molecular weights (MW) were infused into the left atria of six pentobarbital-anesthetized dogs (group 1). The unidirectionally ventilated trachea behaved as a high ventilation-perfusion unit (ratio = 60) with no appreciable dead space. Excretion of higher-MW gases appeared to be depressed, suggesting a MW dependence to inert gas exchange. This was further explored in another six dogs (group 2) with three gases of nearly equal solubility but widely divergent MWs (acetylene, 26; Freon-22, 86.5; isoflurane, 184.5). Isoflurane and Freon-22 excretions were depressed 47 and 30%, respectively, relative to acetylene. In a theoretical model of airway gas exchange, neither a tissue nor a gas phase diffusion resistance predicted our results better than the standard equation for steady-state alveolar inert gas elimination. However, addition of a simple ln (MW) term reduced the remaining residual sum of squares by 40% in group 1 and by 83% in group 2. Despite this significant MW influence on tracheal gas exchange, we calculate that the quantitative gas exchange capacity of the conducting airways in total can account for less than or equal to 16% of any MW-dependent differences observed in pulmonary inert gas elimination.

Effects of α-latrotoxin, lanthanides and elevated potassium concentration on acetylcholine release and free intracellular calcium levels in rat cerebral cortex synaptosomes

At peripheral cholinergic nerve terminals, lanthanum (La 3+) increases acetylcholine (ACh) release and supports transmitter release induced by α-latrotoxin (α-LTx). The present experiments investigate these interactions at central cholinergic nerve terminals by measuring the effects of La 3+ and gadolinium (Gd 3+), another element of the lathanide (Ln 3+) series, on ACh release and free intracellular calcium concentrations ([Ca 2+] i) in rat cortical synaptosomal preparations. Ln 3+ had no measurable effect on basal synaptosomal ACh release, ACh contents or [Ca 2+] i. Release of ACh induced by α-LTx was inhibited by the presence of Ln 3+, as were ACh release responses to elevated K +. The rise in [Ca 2+] i induced by α-LTx was inhibited by Ln 3+ at concentrations similar to those that inhibited ACh release. Addition of Ln 3+ subsequent to an α-LTx-evoked increase in [Ca 2+] i resulted in an immediate (within 4 s) cessation of calcium entry. Gd 3+ binding studies using the radioisotope 153Gd 3+ revealed that Gd 3+ bound extremely rapidly to synaptosomes and that under the experimental conditions used to measure either α-LTx- or K +-induced ACh release, little or no free Gd 3+ was likely to exist in the medium. We conclude that at central cholinergic neurons 1-Ln 3+ do not affect basal ACh release and 2-Ln 3+ are effective inhibitors for α-LTx-induced ACh release and changes in [Ca 2+] i.

Oxidative addition of zero-valent lanthanides at transition metal-halogen bonds

Alkyl and aryl iodides add to zero-valent lanthanides to form Grignard-like reagents RLnI. The authors have already studied the addition of Ln(0) at the Hg-I bond in HgI/sub 2/ and RHgI compounds to give bimetallic derivatives of divalent lanthanides. In the present work, preliminary results are given for a study of the reactions of rare-earth elements with metal carbonyl halides with the general formula L(OC)/sub m/M-X (I), where L(OC)/sub m/M = Cp(OC)/sub 3/Cr, Cp(OC)/sub 3/Mo, Cp(OC)/sub 3/W, (OC)/sub 5/Mn, (OC)/sub 5/Re, or Cp(OC/sub 2/)Fe and X = Cl, BR, or I.