Quasirelativistic f-in-core pseudopotentials and core-polarization potentials for trivalent actinides and lanthanides: molecular test for trifluorides

Calibration studies of actinide and lanthanide trifluorides are reported for actinide and lanthanide scalar-relativistic energy-consistent f-in-core pseudopotentials, respectively, accompanying valence basis sets as well as core-polarization potentials. Results from Hartree–Fock and coupled-cluster singles, doubles, and perturbative triples f-in-core pseudopotential calculations are compared to corresponding data from f-in-valence pseudopotential and all-electron calculations as well as to experimental data. In general, good agreement is observed between the f-in-core and f-in-valence pseudopotential results, whereas due to the lack of experimental data for the actinides only a good agreement of the calculated and experimentally determined bond lengths of the lanthanide systems can be established. Nevertheless, the results indicate that the core-polarization potentials devised here for actinides improve the f-in-core results.     

Sorption behavior of Am<Superscript>3+</Superscript> on suspended pyrite

Sorption behavior of ²⁴¹Am (~10⁻⁹ M) on naturally occurring mineral pyrite (particle size: ≤70 μm) has been studied under varying conditions of pH (2–11), and ionic strength (0.01–1.0 M (NaClO₄)). The effects of humic acid (2 mg/L), other complexing anions (1 × 10⁻⁴ M CO₃ ²⁻, SO₄ ²⁻, C₂O₄ ²⁻ and PO₄ ³⁻), di- and trivalent metal ions (1 × 10⁻³ M Mg²⁺, Ca²⁺ and Nd³⁺) on sorption behavior of Am³⁺ at a fixed ionic strength (I = 0.10 M (NaClO₄)) have been studied. The sorption of ²⁴¹Am on pyrite increased with pH from 2.8 (84%) to 8.1 (97%). The sorption of ²⁴¹Am decreased with ionic strength at low pH values (2 ≤ pH ≤ 4), but was insensitive in the pH range of 4–10, suggesting the formation of outer-sphere complexes on pyrite surface at lower pH, and inner-sphere complexes at higher pH values. The sorption of ²⁴¹Am increased in the presence of (i) humic acid (5 < pH < 7.5), and (ii) C₂O₄ ²⁻ (2 < pH < 3). By contrast, other complexing anions such as (carbonate, phosphate, and sulphate) showed negligible influence on ²⁴¹Am sorption. The presence of Mg²⁺, Ca²⁺ ions showed marginal effect on the sorption profile of ²⁴¹Am; while the presence of Nd³⁺ ion suppressed its sorption significantly under the conditions of present study. The sorption of ²⁴¹Am on pyrite decreased with increased temperature indicating an exothermic process.     

Quasirelativistic energy-consistent 4f-in-core pseudopotentials for tetravalent lanthanide elements

Quasirelativistic energy-consistent 4f-in-core pseudopotentials modeling tetravalent lanthanides (4f ^n?1 occupation with n = 1, 2, 3, 8, 9 for Ce, Pr, Nd, Tb, Dy) have been adjusted. Energy-optimized (6s5p4d) and (7s6p5d) valence basis sets contracted to polarized double- to quadruple-zeta quality as well as 2f1g correlation functions have been derived. Corresponding smaller (4s4p3d) and (5s5p4d) basis sets suitable for calculations on lanthanide(IV) ions in crystalline solids form subsets of these basis sets designed for calculations on neutral molecules. Calculations for lanthanide tetrafluorides using the 4f-in-core pseudopotentials at the Hartree–Fock level show satisfactory agreement with calculations using 4f-in-valence pseudopotentials. For cerium tetrafluoride the experimental bond length is well reproduced using the 4f-in-core pseudopotential at the coupled-cluster level with single and double excitation operators and a perturbative estimate of triple excitations. For cerium dioxide 4f-in-core and 4f-in-valence pseudopotential calculations agree quite well, if a proper f basis set instead of f polarization functions is applied.     

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 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.     

Quasirelativistic energy-consistent 5f-in-core pseudopotentials for divalent and tetravalent actinide elements

Quasirelativistic energy-consistent 5f-in-core pseudopotentials modeling divalent (5f ⁿ⁺¹ occupation with n = 5–13 for Pu–No) respectively tetravalent (5f ^n-1 occupation with n = 1–9 for Th–Cf) actinides together with corresponding core-polarization potentials have been generated. Energy-optimized (6s5p4d) and (7s6p5d) valence basis sets as well as 2f1g correlation functions have been derived and contracted to polarized double, triple, and quadruple zeta quality. Corresponding smaller (4s4p) and (5s5p) respectively (4s4p3d) and (5s5p4d) basis sets suitable for calculations on actinide(II) respectively actinide(IV) ions in crystalline solids form subsets of these basis sets designed for calculations on molecules. Results of Hartree–Fock test calculations for actinide di- and tetrafluorides show a satisfactory agreement with calculations using 5f-in-valence pseudopotentials. Electronic Supplementary Material The online version of this article doi: contains supplementary material, which is available to authorized users.     

Extraction of metal ions (Fe<Superscript>3+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript>, Cu<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript>) using immobilized-polysiloxane iminobis(n-2-aminophenylacetamide) ligand system

A new insoluble solid functionalized ligand system bearing chelating ligand group of the general formula P-(CH₂)₃-N[CH₂CONH(C₆H₄)NH₂]₂, where P represents [Si–O] _n polysiloxane network, was prepared by the reaction of the immobilized diethyliminodiacetate polysiloxane ligand system, P-(CH₂)₃N(CH₂CO₂Et)₂ with 1,2-diaminobenzene in toluene. ¹³C CP-MAS NMR, XPS and FTIR results showed that most ethylacetate groups (–COOEt) were converted into the amide groups (–N–C=O). The new functionalized ligand system exhibits high capacity for extraction and removal of the metal ions (Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺) with efficiency of 95–97% after recovery from its primary metal complexes. This functionalized ligand system formed 1:1 metal to ligand complexes.     

Thermodynamics of citrate complexation with Mn<Superscript>2+</Superscript>, Co<Superscript>2+</Superscript>, Ni<Superscript>2+</Superscript> and Zn<Superscript>2+</Superscript> ions

Isothermal titration calorimetry has been used to determine the stoichiometry, formation constants and thermodynamic parameters (ΔG ^o, ΔH, ΔS) for the formation of the citrate complexes with the Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺ ions. The measurements were run in Cacodylate, Pipes and Mes buffer solutions with a pH of 6, at 298.15 K. A constant ionic strength of 100 mM was maintained with NaClO₄. The influence of a metal ion on its interaction energy with the citrate ions and the stability of the resulting complexes have been discussed.     

Gd<Superscript>3+</Superscript> binding of carboxylated polyglycidyl methacrylate latices and their colloidal stability

The binding of Gd³⁺ to two carboxylated polyglycidyl methacrylate latices was investigated. The latices differed in size (60 and 140 nm for CL6 and CL3, respectively) and surface charge density. The Gd³⁺ concentration in aqueous suspension was determined using an arsenazo (III) assay. Using ¹⁵³Gd³⁺, the bound amount was determined directly. Because of the high binding affinity, ligand depletion became evident. The binding was pH dependent, investigated in buffer solutions not influencing the arsenazo (III) assay. Optimal binding occurs by formation of sodium salts of the carboxylic groups and replacement of Na⁺ and H⁺ by Gd³⁺. The dissociation constants of the particles were k _D ≈ 5 × 10⁻⁵ mol/L (CL3) and 10⁻⁴ mol/L (CL6), without cooperativity (Hill plot). Colloidal stability was investigated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Quasirelativistic energy-consistent 5f-in-core pseudopotentials for trivalent actinide elements

Quasirelativistic energy-consistent 5f-in-core pseudopotentials modelling trivalent actinides, corresponding to a near-integral 5f ⁿ occupation (n = 0–14 for Ac–Lr), have been generated. Energy-optimized (6s5p4d), (7s6p5d), and (8s7p6d) primitive valence basis sets contracted to polarized double to quadruple zeta quality as well as 2f1g correlation functions have been derived. Corresponding smaller basis sets (4s4p3d), (5s5p4d), and (6s6p5d) suitable for calculations on actinide(III) ions in crystalline solids form subsets of these basis sets designed for calculations on neutral molecules. Results of Hartree–Fock test calculations for actinide(III) monohydrates and actinide trifluorides show a satisfactory agreement with corresponding calculations using 5f-in-valence pseudopotentials. Even in the beginning of the actinide series, where the 5f shell is relatively diffuse, only quite acceptable small deviations occur as long as the 5f-shell does not participate significantly in covalent bonding. Electronic Supplementary Material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

PuPO<Subscript>4</Subscript>(cr,hyd.) Solubility Product and Pu<Superscript>3+</Superscript> Complexes with Phosphate and Ethylenediaminetetraacetic Acid

To determine the solubility product of PuPO₄(cr, hyd.) and the complexation constants of Pu(III) with phosphate and EDTA, the solubility of PuPO₄(cr, hyd.) was investigated as a function of: (1) time and pH (varied from 1.0 to 12.0), and at a fixed 0.00032 mol⋅L⁻¹ phosphate concentration; (2) NaH₂PO₄ concentrations varying from 0.0001 mol⋅L⁻¹ to 1.0 mol⋅L⁻¹ and at a fixed pH of 2.5; (3) time and pH (varied from 1.3 to 13.0) at fixed concentrations of 0.00032 mol⋅L⁻¹ phosphate and 0.0004 mol⋅L⁻¹ or 0.002 mol⋅L⁻¹ Na₂H₂EDTA; and (4) Na₂H₂EDTA concentrations varying from 0.00005 mol⋅L⁻¹ to 0.0256 mol⋅L⁻¹ at a fixed 0.00032 mol⋅L⁻¹ phosphate concentration and at pH values of approximately 3.5, 10.6, and 12.6. A combination of solvent extraction and spectrophotometric techniques confirmed that the use of hydroquinone and Na₂S₂O₄ helped maintain the Pu as Pu(III). The solubility data were interpreted using the Pitzer and SIT models, and both provided similar values for the solubility product of PuPO₄(cr, hyd.) and for the formation constant of PuEDTA⁻. The log ₁₀ of the solubility product of PuPO₄(cr, hyd.) [PuPO₄(cr, hyd.) \rightleftarrows\rightleftarrows Pu³⁺+PO₄^3-\mathrm{Pu}^{3+}+\mathrm{PO}_{4}^{3-}] was determined to be −(24.42±0.38). Pitzer modeling showed that phosphate interactions with Pu³⁺ were extremely weak and did not require any phosphate complexes [e.g., PuPO₄(aq), PuH₂PO₄²⁺\mathrm{PuH}_{2}\mathrm{PO}_{4}^{2+}, Pu(H₂PO₄)₂⁺\mathrm{Pu(H}_{2}\mathrm{PO}_{4})_{2}^{+}, Pu(H₂PO₄)₃(aq), and Pu(H₂PO₄)₄^-\mathrm{Pu(H}_{2}\mathrm{PO}_{4})_{4}^{-}] as proposed in existing literature, to explain the experimental solubility data. SIT modeling, however, required the inclusion of PuH₂PO₄²⁺\mathrm{PuH}_{2}\mathrm{PO}_{4}^{2+} to explain the data in high NaH₂PO₄ concentrations; this illustrates the differences one can expect when using these two different chemical models to interpret the data. Of the Pu(III)-EDTA species, only PuEDTA⁻ was needed to interpret the experimental data over a large range of pH values (1.3–12.9) and EDTA concentrations (0.00005–0.256 mol⋅L⁻¹). Calculations based on density functional theory support the existence of PuEDTA⁻ (with prospective stoichiometry as Pu(OH₂)₃EDTA⁻) as the chemically and structurally stable species. The log ₁₀ value of the complexation constant for the formation of PuEDTA⁻ [ Pu³⁺+EDTA^4-\rightleftarrows PuEDTA^-\mathrm{Pu}^{3+}+\mathrm{EDTA}^{4-}\rightleftarrows \mathrm{PuEDTA}^{-}] determined in this study is −20.15±0.59. The data also showed that PuHEDTA(aq), Pu(EDTA)₄^5-\mathrm{Pu(EDTA)}_{4}^{5-}, Pu(EDTA)(HEDTA)⁴⁻, Pu(EDTA)(H₂EDTA)³⁻, and Pu(EDTA)(H₃EDTA)²⁻, although reported in the literature, have no region of dominance in the experimental range of variables investigated in this study.     

Quasirelativistic energy-consistent 5f-in-core pseudopotentials for pentavalent and hexavalent actinide elements

Quasirelativistic energy-consistent 5f-in-core pseudopotentials modeling pentavalent (5f ^n?2 occupation with n = 2–6 for Pa–Am) and hexavalent (5f ^n?3 occupation with n = 3–6 for U–Am) actinides have been adjusted. Energy-optimized (6s5p4d) and (7s6p5d) valence basis sets contracted to polarized double- to quadruple-zeta quality as well as 2f1g correlation functions have been derived. Corresponding smaller basis sets (4s4p3d) and (5s5p4d) suitable for calculations on actinide(V) and actinide(VI) ions in crystalline solids form subsets of these basis sets designed for calculations on neutral molecules. Calculations using the Hartree–Fock and the coupled-cluster method with single and double excitation operators and a perturbative estimate of triple excitations for actinide pentafluorides show satisfactory agreement with calculations using 5f-in-valence pseudopotentials and experimental data, respectively. However, in the hexavalent case the 5f-in-core approximation seems to reach its limitations except for hexavalent uranium (5f⁰), where results for both uranium hexafluoride and the uranyl ion deviate only slightly from the 5f-in-valence reference data.     

Photoluminescence in Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>-doped silica-titania inverse opal structures

Er³⁺ photoluminescence (PL) and Yb³⁺ → Er³⁺ energy transfer (ET) phenomena in the near infrared (NIR) have been studied in three-dimensional (3-D) inverse opal (IO) structures synthesized by a colloidal/sol–gel route, starting with the deposition of polystyrene microsphere (235 nm and 460 nm diameter) direct opal templates by convective self-assembly, followed by infiltration of the interstices with Er³⁺/Yb³⁺-doped silica, titania and silica-titania sols and heat-removal of the polymeric template material. The crystalline quality of the IOs has been optimized through suitable substrate treatments, plus the control of temperature and humidity during deposition of the templates. The structural and optical properties of the 3-D opal and IO structures have been studied by field emission scanning electron microscopy and visible-NIR reflection spectroscopy, in order to assess the relationship between microstructure and the photonic properties obtained. Photonic bandgaps have been evidenced by the corresponding stop bands in the reflection spectra. The shape and the intensity of the Er^{3+ 4}I_13/2 → ⁴I_15/2 transition at ~1.5 μm were modified in most IOs relatively to similar matrix deposits without a photonic crystal structure, particularly in the case of pure silica and titania IOs, where the PL peak narrowed and intensified. It was not possible at this stage to detect Yb³⁺ → Er³⁺ ET phenomena in the IOs structures.     

Study on physicochemical properties of U<Superscript>3+</Superscript> in LiCl–KCl eutectic media at 773 K

In order to enhance the efficiency of pyrochemical technology, especially electrorefining process, physicochemical data of trivalent uranium in LiCl–KCl eutectic at 773 K were measured, including molar absorptivity, formal potential and diffusion coefficient of U³⁺ ions. The molar absorptivities of U³⁺ were determined to be 765 ± 48 and 686 ± 39 M⁻¹ cm⁻¹ at 465 and 550 nm, respectively. The formal potential of U³⁺/U⁴⁺ redox couple and diffusion coefficient of U³⁺ ions were measured to be −0.308 V vs. Ag/Ag⁺ and 8.7 × 10⁻⁶ M⁻¹ cm⁻¹, respectively. To elucidate the chemical behavior of U³⁺ ions under the existence of oxide ions, U³⁺ ions were reacted with oxides ions in situ produced at the LiCl–KCl media. Surprisingly, it was revealed from XRD patterns that UO₂ was formed from the reaction between U³⁺ ions and O²⁻ ions with the molar ratio of 1:1.     

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]⁺.     

Opposite effect of Li<Superscript>+</Superscript> codoping on the upconversion emissions of Er<Superscript>3+</Superscript>-doped TiO<Subscript>2</Subscript> powders

The Er³⁺-Li⁺ codoped TiO₂ powders have been prepared by the non-aqueous sol–gel method. The green and red upconversion emissions centered at about 526, 550 and 663 nm were observed by the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively. Li⁺ codoping has opposite effect on the upconversion emissions intensities for Er³⁺-doped TiO₂ at sintering temperatures of 1,073 and 1,273 K. At 1,073 K, the Er³⁺-doped TiO₂ phase transition from anatase to rutile was accelerated with increasing Li⁺ codoping concentration, leading to the increase of crystal field symmetry of Er³⁺, thus the upconversion emissions intensities decreased. At 1,273 K, Li⁺ codoping had no effect on the phase structure of Er³⁺-doped TiO₂ and only increased the Er–O bond length, it indicated that the upconversion emissions intensities greatly enhanced because of the decrease of crystal field symmetry of Er³⁺.     

Effects of La<Superscript>3+</Superscript> on inward K<Superscript>+</Superscript> 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 K _i of 2.56±0.25 μmol · 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.     

Synthesis,DNA-binding and photocleavage studies of cobalt(III) complexes [Co(bpy)<Subscript>2</Subscript>(dpta)]<Superscript>3+</Superscript> and [Co(bpy)<Subscript>2</Subscript>(amtp)]<Superscript>3+</Superscript>

Two novel cobalt(III) mixed-polypyridyl complexes [Co(bpy)₂(dpta)]³⁺ and [Co(bpy)₂(amtp)]³⁺ (bpy = 2,2′-bipyridine, dpta = dipyrido-[3,2-a;2′,3′-c]-thien-[3,4-c]azine, amtp = 3-amino-1,2,4-triazino[5,6-f]-1,10-phenanthroline) have been synthesized and characterized. The interaction of Co^III complexes with calf thymus DNA was investigated by spectroscopic and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, Co^III complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. The mechanism studies reveal that hydroxyl radical (OH^•) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(bpy)₂(dpta)]³⁺ and superoxide anion radical (O ₂ ^•− ) acts as the key role in the cleavage reaction of plasmid DNA by [Co(bpy)₂(amtp)]³⁺.     

Ionic mobility in heptafluorozirconantes with a mixed cationic sublattice as probed by <Superscript>1</Superscript>H and <Superscript>19</Superscript>F NMR

The ionic mobility in heptafluorozirconates (NH₄)_2.7Rb_0.3ZrF₇ and (NH₄)_2.75Cs_0.25ZrF₇ has been studied by ¹H and ¹⁹F NMR in the temperature range 150–430 K. The types of ion motion were determined and their activation energies were estimated. A phase transition results in a modification in which diffusion in the ammonium sublattice and orientational disorder of ZrF₇³⁻ anions are observed. Owing to diffusion of ammonium ions, the compounds have relatively high ionic conductivity (σ ≥ 5 × 10⁻⁵ S/cm at 420 K).     

Preparation of <Superscript>99m</Superscript>Tc-PQQ and preliminary biological evaluation for the NMDA receptor

Pyrroloquinoline quinone (PQQ), an essential nutrient, antioxidant, redox modulator and nerve growth factor found in a class of enzymes called quinoproteins, was labeled with ^99mTc by using stannous fluoride (SnF₂) method. Radiolabeling qualification, quality control and characterization of ^99mTc-PQQ and its biodistribution studies in mice were performed and discussed. Effects of pH values, temperature, time and reducing agents concentration on the radiolabeling yield were investigated. The quality control procedure of ^99mTc-PQQ was determined by thin layer chromatography (TLC), radio high-performance liquid chromatography (RHPLC) and paper electrophoresis methods. The average radiolabeling yield was 94 ± 1% under optimum conditions of 0.99 mg of PQQ, 30 μg of SnF₂, 0.5 mg of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and 18.5 MBq of Na^99mTcO₄ at pH 6 and 25 °C with a response volume of 1 ± 0.1 mL. ^99mTc-PQQ was stable and anionic. Lipid–water partition coefficient of ^99mTc-PQQ was −1.49 ± 0.16. The pharmacokinetics parameters of ^99mTc-PQQ were t _1/2α = 18.16 min, t _1/2β = 100.45 min, K ₁₂ = 0.013 min⁻¹, K ₂₁ = 0.017 min⁻¹, K _e = 0.016 min⁻¹, AUC (area under the curve) = 1040.78 ID% g⁻¹ min and CL (plasma clearance) = 0.096 mL min⁻¹. The dual-exponential equation was Y = 10.88e^−0.038t  + 5.21e^−0.0069t . The biodistribution of ^99mTc-PQQ was studied in ICR (Institute for Cancer Research 7701 Burhelme Are., Fox Chase, Philadelphia, PA 1911 USA) mice. In vitro autoradiographic studies clearly showed that the ^99mTc-PQQ radioactivity accumulated predominantly in the hippocampus and cortex, which had a high density of N-methyl-d-aspartate Receptor (NMDAR). The enrichment can be blocked by NMDAR redox modulatory site antagonists-ebselen (EB) and ^99mTc-PQQ is therefore a promising candidate for the molecular imaging of NMDAR. To date, however, there have been no studies characterizing ^99mTc-PQQ.