Effects of La<Superscript>3+</Superscript> and Eu<Superscript>3+</Superscript> on outward potassium channels in Vicia guard cells

Effects of La³⁺ and Eu³⁺ on outward potassium channels (K_out⁺) in Vicia guard cells have been studied by patch clamping technique. Extracellular La³⁺ inhibited K_out⁺ currents with a half-inhibition concentration (IC₅₀) of 81 μmol·L⁻¹. Interestingly, intracellular La³⁺ activated K_out⁺ currents at a free concentration of 1.13 × 10⁻¹⁴ mol·L⁻¹, and inhibited K_out⁺ currents at a free concentration of 5.86 × 10⁻¹⁴ mol·L⁻¹. Extracellular Eu³⁺ also activated K_out⁺ currents at concentrations of 10 μmol·L⁻¹ and 50 μmol·L⁻¹, and inhibited K_out⁺ currents at concentrations of more than 1 mmol·L⁻¹. The effects of La³⁺ and Eu³⁺ on K_out⁺ currents may contribute to regulation of the plant water status, which may be one of the mechanisms of the biological effect of rare earth elements.     

Solubility and hydrolysis of lutetium at different [Lu<Superscript>3+</Superscript>]<Subscript>initial</Subscript>

Solubility product (Lu(OH)_3(s)⇆Lu³⁺+3OH⁻) and first hydrolysis (Lu³⁺+H₂O⇆Lu(OH)²⁺+H⁺) constants were determined for an initial lutetium concentration range from 3.72·10⁻⁵ mol·dm⁻³ to 2.09·10⁻³ mol·dm⁻³. Measurements were made in 2 mol·dm⁻³ NaClO₄ ionic strength, under CO₂-free conditions and temperature was controlled at 303 K. Solubility diagrams (pLu_aq vs. pC _H) were determined by means of a radiochemical method using ¹⁷⁷Lu. The pC _H for the beginning of precipitation and solubility product constant were determined from these diagrams and both the first hydrolysis and solubility product constants were calculated by fitting the diagrams to the solubility equation. The pC _H values of precipitation increases inversely to [Lu³⁺]_initial and the values for the first hydrolysis and solubility product constants were log₁₀ β* _Lu,H = −7.92±0.07 and log₁₀ K*_sp,Lu(OH)3 = −23.37±0.14. Individual solubility values for pC _H range between the beginning of precipitation and 8.5 were S _Lu3+ = 3.5·10⁻⁷ mol·dm⁻³, S _Lu(OH)2+ = 6.2·10⁻⁷ mol·dm⁻³, and then total solubility was 9.7·10⁻⁷ mol·dm⁻³.     

Effects of La3+ on inward K+ channels at plasma membrane in guard cells

The effects of La3+ on inward K+ channels at plasma membrane in vicia guard cells are investigated using the whole-cell patch-clamp recording mode. It is shown that La3+ on both sides of plasma membrane blocks inward K+ currents in a concentration- dependent manner, indicating that La3+ binding sites may exist on both sides of plasma membrane in guard cells in vicia. The dose response is fitted by the Michaelis-Menten relation characterized by an inhibitor constant Ki of 2.56±0.25μmol·L-1 (outside membrane) and (1.18±0.11)×10-15 mol·L-1 (inside membrane). Intracellular La3+ has much stronger inhibitory effect on inward K+ currents than extracellular La3+ does, suggesting there may exist stronger binding sites inside membrane than outside membrane. Since ion channel activities of guard cells directly affect plant stomatal movement and water status, our results imply that rare earth elements might have potential practical values in regulating plant water status and strengthening plant drought endurance.     

IR and <Superscript>31</Superscript>P NMR spectroscopic study of complexation of carbamoyl methyl phosphinates with U<Superscript>VI</Superscript> and Th<Superscript>IV</Superscript> in nitric acid solutions

The composition of complexes formed upon the extraction of U^VI and Th^IV nitrates with O-n-nonyl(N,N-dibutylcarbamoylmethyl) methyl phosphinate (L) from solutions of nitric acid without additional solvent was determined by ³¹P NMR spectroscopy. The structures of the complexes formed were studied by IR spectroscopy. Uranium(VI) is extracted from 3 and 5 M solutions of HNO₃ as the [UO₂(L)₂(NO₃)₂] complex, while thorium(IV) is extracted from 5 M HNO₃ as the [Th(L)₃(NO₃)₃]⁺·NO ₃ ⁻ complex. In both cases, ligand L has bidentate coordination. Ligand L contacts with 3 and 5 M nitric acid to form adducts L·HNO₃ and L· (HNO₃)₂, respectively. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2460–2464, November, 2005.     

Functionalization of one or two methyl groups in the [Cp*<Subscript>2</Subscript>RuBr]<Superscript>+</Superscript>Br<Superscript>−</Superscript> complex in the reaction with bromine

The reaction of [Cp*₂RuBr]⁺Br⁻ with bromine in CH₂Cl₂ (CD₂Cl₂) in an inert atmosphere at room temperature produces the complexes [Cp*Ru(Br)C₅Me₄CH₂Br]⁺Br₃ ⁻ (syn conformer), [Cp*Ru(Br)C₅Me₃(CH₂Br)₂]⁺ (syn and anti conformers), and [Ru(Br)(C₅Me₄CH₂Br)₂]⁺ (syn conformer). All complexes were characterized by ¹H and ¹³C NMR spectroscopy; the former complex, by elemental analysis. These complexes were also prepared by the reaction of [Cp*RuC₅Me₄CH₂]⁺BF₄ ⁻ with bromine in CH₂Cl₂. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2712–2718, December, 2005.     

Ion-exchange selectivity of a network calixarene-containing polymer obtained by the template synthesis on Na<Superscript>+</Superscript>, K<Superscript>+</Superscript>, and Ba<Superscript>2+</Superscript> matrices

The ion-exchange equilibrium in network polymers obtained from cis-2,8,14,20-tetraphenyl-4,6,10,12,16,18,22,24-octahydroxycalix[4]arene by template synthesis on cations Na⁺, K⁺, and Ba²⁺ as matrices was studied. The selectivity coefficients of ion exchanges Ba²⁺-H⁺, Na⁺-H⁺, K⁺-H⁺, Na⁺-K⁺, and Na⁺-NH₄ ⁺ were determined. The template synthesis enhanced the affinity of the polymers to matrix-forming cations by 6–8 kJ mol⁻¹. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1919–1922, August, 2005.     

Combination of <Superscript>13</Superscript>C/<Superscript>113</Superscript>Cd NMR,potentiometry, and voltammetry in characterizing the interactions between Cd and two models of the main components of soil organic matter

This work allowed the characterization of the Cd-binding sites of two compounds taken as models for exudates, the main components of soil organic matter (SOM). The studied compounds were exopolysaccharides (EPS), specifically exudates of roots (polygalacturonic acid) and of soil bacteria (Phytagel). Potentiometric acid–base titrations were performed and fitting of the obtained results indicated the presence of two main classes of acidic sites, defined by their pK _a values, for both EPS but of a different nature when comparing the two compounds. The two studied exopolysaccharides presented different acidic/basic site ratios: 0.15 for Phytagel and 0.76 for polygalacturonic acid. Spectroscopic techniques (¹³C/¹¹³Cd NMR, FTIR) distinguished different Cd surroundings for each of the studied EPS, which is in agreement with the titration results. Furthermore, these analyses indicated the presence of –COOH and –OH groups in various proportions for each exopolysaccharide, which should be linked to their reactivity towards cadmium. Cadmium titrations (voltammetric measurements) also differentiated different binding sites for each compound and allowed the determination of the strength of the Cd-binding site of the EPS. Fitting of the results of such voltammetric measurements was performed using PROSECE (Programme d’Optimisation et de Speciation Chimique dans l’Environnement), a software coupling chemical speciation calculation and binding parameter optimization. The fitting, taking into account the Cd²⁺/H⁺ competition towards exopolysaccharides, confirmed the acid-base titrations and spectroscopic analyses by revealing two classes of binding sites: (i) one defined as a strong complexant regarding its Cd²⁺–EPS association (logK = 9–10.4) and with basic functionality regarding H⁺–EPS association (pK _a = 11.3–11.7), and (ii) one defined as a weak complexant (logK = 7.1–8.2) and with acidic functionality (pK _a = 3.7–4.0). Therefore the combination of spectroscopic analyses, voltammetry, and fitting allowed the precise characterization of the binding sites of the studied exopolysaccharides, mimicking the main SOM components. Furthermore, the binding parameters obtained by fitting can be used in biogeochemical models to better define the role of key SOM compounds like exudates of roots and of soil bacteria on trace metal transport or assimilation.     

Removal of <Superscript>60</Superscript>Co<Superscript>2+</Superscript> and <Superscript>137</Superscript>Cs<Superscript>+</Superscript> ions from low radioactive solutions using <Emphasis Type="Italic">Azolla caroliniana</Emphasis> willd. water fern

This study concerns the removal of the ¹³⁷Cs⁺ and ⁶⁰Co²⁺ β+γ-radioactive ions in Azolla caroliniana Willd. water fern. The living fern and two different types of biosorbent prepared from Azolla caroliniana were tested to remove the above-mentioned radioactive ions from dilute solutions, in the absence and in the presence of the ionic competition. Effective ¹³⁷Cs⁺ and ⁶⁰Co²⁺ ions removal from low radioactive wastewaters was demonstrated. The time dependent K _d (t) values were calculated from the absorption data. These results indicate that removal process achieved equilibrium in about 120 min and that it involves two steps: rapid and slow absorption; the active process (metabolic bioaccumulation on the living fern) was responsible for above one half of the total removal process. A thin layer radiochromatography study leads to the conclusion that the biochemical components in which ¹³⁷Cs⁺ and ⁶⁰Co²⁺ place themselves are of a polysaccharide and lipoid fractions.     

Novel methodology for the study of mercury methylation and reduction in sediments and water using <Superscript>197</Superscript>Hg radiotracer

Mercury tracers are powerful tools that can be used to study mercury transformations in environmental systems, particularly mercury methylation, demethylation and reduction in sediments and water. However, mercury transformation studies using tracers can be subject to error, especially when used to assess methylation potential. The organic mercury extracted can be as low as 0.01% of the endogenous labeled mercury, and artefacts and contamination present during methylmercury (MeHg) extraction processes can cause interference. Solvent extraction methods based on the use of either KBr/H₂SO₄ or HCl were evaluated in freshwater sediments using ¹⁹⁷Hg radiotracer. Values obtained for the ¹⁹⁷Hg tracer in the organic phase were up to 25-fold higher when HCl was used, which is due to the coextraction of ¹⁹⁷Hg²⁺ into the organic phase during MeHg extraction. Evaluations of the production of MeHg gave similar results with both MeHg extraction procedures, but due to the higher Hg²⁺ contamination of the controls, the uncertainty in the determination was higher when HCl was used. The Hg²⁺ contamination of controls in the HCl extraction method showed a nonlinear correlation with the humic acid content of sediment pore water. Therefore, use of the KBr/H₂SO₄ method is recommended, since it is free from these interferences. ¹⁹⁷Hg radiotracer (T _1/2 = 2.673 d) has a production rate that is about 50 times higher than that of ²⁰³Hg (T _1/2 = 46.595 d), the most frequently used mercury radiotracer. Hence it is possible to obtain a similar level of performance to ²⁰³Hg when it is used it in short-term experiments and produced by the irradiation of ¹⁹⁶Hg with thermal neutrons, using mercury targets with the natural isotopic composition. However, if the 0.15% natural abundance of the ¹⁹⁶Hg isotope is increased, the specific activity of the ¹⁹⁷Hg tracer can be significantly improved. In the present work, ¹⁹⁷Hg tracer was produced from mercury 51.58% enriched in the ¹⁹⁶Hg isotope, and a 340-fold increase in specific activity with respect to natural mercury targets was obtained. When this high specific activity tracer is employed, mercury methylation and reduction experiments with minimum mercury additions are feasible. Tracer recovery in methylation experiments (associated with Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike, but also with Hg²⁺ contamination and Me¹⁹⁷Hg artefacts) with marine sediments was about 0.005% g⁻¹ WS (WS: wet sediment) after 20 h incubation with mercury additions of 0.05 ng g⁻¹ WS, which is far below natural mercury levels. In this case, the amount of Hg²⁺ reduced to Hg⁰ (expressed as the percent ¹⁹⁷Hg⁰ recovered with respect to the ¹⁹⁷Hg²⁺ added) varied from 0.13 to 1.6% g⁻¹ WS. Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike after 20 h of incubation of freshwater sediment ranged from 0.02 to 0.13% g⁻¹ WS with mercury additions of 2.5 ng g⁻¹ WS, which is also far below natural levels. ¹⁹⁷Hg⁰ recoveries were low, 0.0058 ± 0.0013% g⁻¹ WS, but showed good reproducibility in five replicates. Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spiked in freshwater samples ranged from 0.1 to 0.3% over a period of three days with mercury additions of 10 ng L⁻¹. A detection limit of 0.05% for Me¹⁹⁷Hg production from ¹⁹⁷Hg²⁺ spike was obtained in seawater in a 25 h incubation experiment with mercury additions of 12 ng L⁻¹.     

Molecular modeling of hydration properties of hydrophobic ions Li<Superscript>+</Superscript>@C<Subscript>60</Subscript> and K<Superscript>+</Superscript>@C<Subscript>60</Subscript>

The Gibbs free energies of solvation (ΔG _s) and the electronic structures of endohedral metallofullerenes M⁺@C₆₀ (M⁺= Li⁺, K⁺) were calculated within the framework of the density functional theory and the polarizable continuum model. In water environment, the equilibrium position of K⁺ is at the center of the fullerene cavity whereas that of Li⁺ is shifted by 0.14 nm toward the fullerene cage. The Li⁺ cation is stabilized by interactions with both the fullerene and solvent. The equilibrium structures of both endohedral metallofullerenes are characterized by very close ΔG _s values. In particular, the calculated ΔG _s values for K⁺@C₆₀ are in the range from −124 to −149 kJ mol⁻¹ depending on the basis set and on the type of the density functional. Molecular dynamics simulations (TIP3P H₂O, OPLS force field, water sphere of radius 1.9 nm) showed that the radial distribution functions of water density around C₆₀ and M⁺@C₆₀ are very similar, whereas orientations of water dipoles around the endohedral metallofullerenes resemble the hydration pattern of isolated metal ions.     

Second Dissociation Constant of H<Subscript>2</Subscript>Te and the Absorption Spectra of HTe<Superscript>–</Superscript>, Te<Superscript>2–</Superscript> and Te<Subscript>2</Subscript><Superscript>2–</Superscript> in Aqueous Solution

We have measured the second acid dissociation constant, K _2a , at several ionic strengths for hydrogen telluride (H₂Te) using the Charge Transfer to Solvent (CTTS) uv spectra of its anions HTe⁻ and Te²⁻. Since it is produced in our solutions, we have also determined the spectra of Te₂ ²⁻ both in the uv and in the visible regions. At 25 ^∘C, K _2a = (1.28 ± 0.02) × 10⁻¹² by extrapolation to zero ionic strength. Its value at an ionic strength equal to 0.5 mol.dm^-3 was estimated to be (8.7 ± 0.2) × 10⁻¹². The solution thermodynamics of these species are also discussed and comparisons are made to related acids.     

Aluminum Solvate Complexes Forming in Acidic Methanol-Acetone Mixtures Studied by <Superscript>27</Superscript>Al NMR Spectroscopy

²⁷Al NMR spectroscopy is a powerful tool for the study of coordination and solvation in both aqueous and nonaqueous solutions. In this study, the complexes coexisting upon dissolution of AlCl₃ in acidic acetone + methanol solutions are shown to consist essentially of mixed hexacoordinated species of the general formula [Al(CH₃OH)_6−n (CH₃COCH₃) _n ]³⁺ (n=1,2 and 3), all exhibiting distinctly different ²⁷Al shielding effects. The relative populations of the various mixed species are found to be highly dependent upon the acetone:methanol mole ratio that in the more acetone-rich mixtures with aluminum become appreciably coordinated by acetone. The results demonstrate that the key factor for the formation of acetone-containing species in acidic methanolic solutions is having the CH₃COCH₃:CH₃OH mole ratio at 3:1.     

Local structure and photoluminescent characteristics of Eu<Superscript>3+</Superscript> in ZnO–SiO<Subscript>2</Subscript> glasses

The photoluminescence properties of xZnO–(100−x)SiO₂ (x = 0, 5, 10, 20) containing 1% Eu₂O₃ prepared by a sol–gel method were systematically investigated. The results indicated that the relative proportion of f–f transitions to charge transfer (CT) absorption decreased with the increase of ZnO concentration. The intensity of ⁵D₀–⁷F_J transitions of Eu³⁺ ions was enhanced with the increase of ZnO content due to local structure changes and decreased quantities of Eu³⁺ ions clusters. The results of fluorescence line narrow (FLN) spectra indicated that Eu³⁺ ions occupied one site in SiO₂ glass and two sites in ZnO–SiO₂ glasses. The second-order crystal field parameters were calculated. B₂₀ and B₂₂ for site 1 increased with excitation energy, while ones hardly changed for site 2.     

Critical phenomena in ethylbenzene oxidation in acetic acid solution at high cobalt(<Emphasis Type="SmallCaps">II</Emphasis>) concentrations

Critical phenomena in ethylbenzene oxidation in an acetic acid solution at high cobalt(III) concentrations (from 0.01 to 0.2 mol L⁻¹) were studied at 60–90 °C by the gasometric (O₂ absorption), spectrophotometric (Co^III accumulation), and chemiluminescence (relative concentration of radical RO₂ ^·) methods. These phenomena are as follows: (1) increase in the oxidation rate above the theoretical limiting rate of radical autooxidation (k ₃ ²[RH]²/2k ₆); (2) achievement of a maximum and a sharp decrease in the oxidation rate and concentration of radical RO₂ ^· with the further increase in the Co^II concentration (existence of critical concentrations). The oxidation rate increases due to the reaction RO₂ ^· + Co^II + H⁺ → → ROOH + Co^III, while the inhibition effect is caused by the decay of RO₂ ^· radical involving two cobalt(II) atoms: RO₂ ^· + 2 Co^II → R′CO + Co^III + Co^II (k(70 °C) ≈ 300 L² mol⁻² s⁻¹). The detailed scheme (through the formation of the complex RO₂ ^·Co^II) describing the conjugation of these reactions was proposed. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1823–1827, August, 2005.     

Theoretical study of the mechanism for C-H bond activation in spin-forbidden reaction between Ti<Superscript>+</Superscript> and C<Subscript>2</Subscript>H<Subscript>4</Subscript>

The mechanism of the spin-forbidden reaction Ti⁺(⁴F, 3d²4s¹) + C₂H₄→TiC₂H₂ ⁺ (²A₂) + H₂ on both doublet and quartet potential energy surfaces has been investigated at the B3LYP level of theory. Crossing points between the potential energy surfaces and the possible spin inversion process are discussed by means of spin-orbit coupling (SOC) calculations. The strength of the SOC between the low-lying quartet state and the doublet state is 59.3 cm⁻¹ in the intermediate complex IM1-⁴B₂. Thus, the changes of its spin multiplicity may occur from the quartet to the doublet surface to form IM1-²A₁, leading to a sig-nificant decrease in the barrier height on the quartet PES. After the insertion intermediate IM2, two distinct reaction paths on the doublet PES have been found, i.e., a stepwise path and a concerted path. The latter is found to be the lowest energy path on the doublet PES to exothermic TiC₂H₂ ⁺(²A₂) + H₂ products, with the active barrier of 4.52 kcal/mol. In other words, this reaction proceeds in the following way: Ti⁺+C₂H₄→⁴IC→IM1-⁴B₂→^4,2ISC→IM1-²A₁→[²TS_ins]→IM2→[²TS_MCTS]→IM5→TiC₂H₂ ⁺(²A₂)+H₂. Supported by ‘Qinglan’ Talent Engineering Funds by Tianshui Normal University.     

Photochemical properties of a new kind of anti-cancer drug: <Emphasis Type="Italic">N</Emphasis>-glycoside compound

Due to the nontoxicity and efficient anti-cancer activity, more and more attention has been paid to N-glycoside compounds. Laser photolysis of N-(α-D-glucopyranoside) salicyloyl hydrazine (NGSH) has been performed for the first time. The research results show that NGSH has high photosensitivity and is vulnerable to be photo-ionized via a monophotonic process with a quantum yield of 0.02, generating NGSH^+· and hydrated electrons. Under the aerobic condition of cells, the hydrated electrons are very easy to combine with oxygen to generate ¹O₂ and O₂ ⁻, both of which are powerful oxidants that can kill the cancer cells. In addition, NGSH^+· can be changed into neutral radicals by deprotonation with a pK _a value of 4.02 and its decay constant was determined to be 2.55×10⁹dm³·mol⁻¹·s⁻¹. NGSH also can be oxidized by SO₄ ^−· with a rate constant of 1.76×10⁹ dm³·mol⁻¹·s⁻¹, which further confirms the results of photoionization. All of these results suggest that this new N-glycoside compound might be useful for cancer treatment. The same contribution to the work Supported by the National Natural Science Foundation of China (Grant Nos. 30570376 and 50673078) and Shanghai Project (Grant Nos. 06JC14068 and 08ZZ21)     

Scalar-relativistic 5f-in-core pseudopotentials and core-polarization potentials for trivalent actinides: calibration calculations for Ac<Superscript>3+</Superscript>, Cm<Superscript>3+</Superscript> and Lr<Superscript>3+</Superscript> complexes

The performance of recently proposed 5f-in-core pseudopotentials for the trivalent actinides was investigated in calculations for model complexes An³⁺L ⁿ⁻ for three selected actinides (An³⁺ = Ac³⁺, Cm³⁺, Lr³⁺) and eight simple ligands with atoms from the first three periods of the table of elements (L ⁿ⁻ = F⁻, Cl⁻, OH⁻, SH⁻, CO, NH₂⁻, H₂O, H₂S, NH₃). Results of Hartree-Fock and Coupled Cluster with singles, doubles and perturbative triples calculations using basis sets of quadruple-zeta quality are compared to corresponding reference data obtained with scalar-relativistic energy-adjusted 5f-in-valence small-core pseudopotentials. The inclusion of core-polarization potentials in the 5f-in-core pseudopotential calculations and corrections of the basis set superposition error by the counterpoise correction leads to very good agreement between the 5f-in-valence and 5f-in-core pseudopotential results for bond lengths, bond angles and binding energies. Results from 5f-in-core pseudopotential calculations using different density functionals also show reasonable agreement with the more rigorous Coupled Cluster results. It is argued that the An 5f rather than the An f population is a useful criterion for the applicability of a specific An 5f-in-core pseudopotential.     

Kinetic and equilibrium study of the deprotonation of 4-nitrophenyl[bis(ethylsulphonyl)]methane by organic bases in acetonitrile in the presence of common cation BH<Superscript>+</Superscript> and tetrabutylammonium perchlorate

The results of kinetic and equilibrium experiments with the set of reaction of proton abstraction from 4-nitrophenyl[bis(ethylsulphonyl)]methane in acetonitrile are reported. Two strong organic bases are used: 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD). The rates of proton transfer reaction have been measured by T-jump method in the presence of perchlorate of the appropriate base as a common cation BH⁺ and supporting electrolyte-tetrabutylammonium perchlorate (TBAP) in the temperature range between 20–40°C are: k _H =1.32×10⁷−2.00×10⁷ and 2.82×10⁷−4.84×10⁷ dm ³mol⁻¹s⁻¹ for MTBD and TBD respectively. The enthalpies of activation ΔH _MTBD ^≠ =13.5 and ΔH _TBD ^≠ =18.1 kJmol⁻¹. The entropies of activation are negative: ΔS _MTBD ^≠ =−62.3 and ΔS _TBD ^≠ =−40.3 Jmol⁻¹K⁻¹. The change of the absorbance of the anion of 4-nitrophenyl[bis9ethylsulphonyl)]methane at the temperature 25°C in the presence of common cation BH⁺ gives the equilibrium constants K=705 and 906 M⁻¹ for MTBD and TBD respectively. Kinetic and equilibrium results are discussed. The possible mechanism of proton transfer reaction between 4-nitrophenyl[bis(ethylsulphonyl)]methane and cyclic organic bases: MTBD and TBD in acetonitrile is proposed.     

A combined experimental and DFT study on the complexation of Mg<Superscript>2+</Superscript> with beauvericin

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Mg²⁺(aq) + 1·Sr²⁺(nb) ⇆ 1·Mg²⁺(nb) + Sr²⁺(aq) taking place in the two-phase water–nitrobenzene system (1 = beauvericin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (Mg²⁺, 1·Sr²⁺) = 0.0 ± 0.1. Further, the stability constant of the 1·Mg²⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C as log β_nb (1·Mg²⁺) = 9.1 ± 0.2. By using quantum mechanical DFT calculations, the most probable structures of the non-hydrated 1·Mg²⁺ and hydrated 1·Mg²⁺·3H₂O complex species were predicted.     

Synthesis of pyridyl derivatives for the future functionalization of biomolecules labeled with the fac-[<Superscript>188</Superscript>Re(CO)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>]<Superscript>+</Superscript> precursor

In this paper, we investigated three ligand systems, symmetric and asymmetric pyridyl-containing tridentate ligands (L¹NH₂ = (bis(2-pyridylmethyl)-amino)-ethylamine, L²H = (bis(2-pyridylmethyl)-amino)-acetic acid, L³NH₂ = [(6-amino-hexyl)-pyridyl-2-methyl-amino]-acetic acid) as bifunctional chelating agents for labeling biomolecules. These ligands reacted with the precursor fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺ and yielded the radioactive complexes fac-[¹⁸⁸Re(CO)₃L] (L = three ligands), which were identified by RP-HPLC. The corresponding stable rhenium tricarbonyl complexes (1–3) were allowed for macroscopic identification of the radiochemical compounds. ¹⁸⁸Re tricarbonyl complexes, with log P _o/w values ranging from −1.36 to −0.32, were obtained with yields of ≥90% using ligand concentrations within the 10⁻⁶−10⁻⁴M range. Challenge studies with cysteine and histidine revealed the high stability properties of these radioactive complexes, and biodistribution studies in normal mice indicated a fast rate of blood clearance and high rate of total radioactivity excretion, primarily through the renal-urinary pathway. In summary, these asymmetric and symmetric pyridyl-containing tridentate ligands are potent bifunctional chelators for the future biomolecules labeling of fac-[¹⁸⁸Re(CO)₃(H₂O)₃]⁺.