Applicability of new spin trap agent, 2-diphenylphosphinoyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide, in biological system

Electron spin resonance using spin-trapping is a useful technique for detecting direct reactive oxygen species, such as superoxide (). However, the widely used spin trap 2,2-dimethyl-3,4-dihydro-2H-pyrrole N-oxide (DMPO) has several fundamental limitations in terms of half-life and stability. Recently, the new spin trap 2-diphenylphosphinoyl-2-methyl-3,4-dihydro-2H-pyrrole N-oxide (DPhPMPO) was developed by us. We evaluated the biological applicability of DPhPMPO to analyze in both cell-free and cellular systems. DPhPMPO had a larger rate constant for and formed more stable spin adducts for than DMPO in the xanthine/xanthine oxidase (X/XO) system. In the phorbol myristate acetate-activated neutrophil system, the detection potential of DPhPMPO for was significantly higher than that of DMPO (k_DMPO = 13.95 M⁻¹ s⁻¹, k_DPhPMPO = 42.4 M⁻¹ s⁻¹). These results indicated that DPhPMPO is a potentially good candidate for trapping in a biological system.     

Polynuclear complex formation of trivalent lanthanides by 5-sulfosalicylate in an aqueous system—potentiometric, H NMR, and TRLIFS studies

The complex formation between several trivalent lanthanides (Ln) and 5-sulfosalicylate, (SSA)³⁻, was investigated by potentiometry, ¹H NMR, and time resolved laser-induced fluorescence spectroscopy (TRLIFS). The potentiometric data were used to deduce the stoichiometry and equilibrium constants for the reactions pLn³⁺ + rL ? Ln_pH_−qL_r + qH⁺ at 298 K in an ionic medium with a constant concentration of Na⁺ equal to 1.00 M. Note that “L” denotes the SSA ligand where all protons are dissociated. Two mononuclear chelating complexes, LnL(aq) and , were identified. Their stability constants obtained by least-squares refinement of the potentiometric data agree well with previously published information. In addition, two additional dinuclear complexes, and , which have very different ¹H NMR and fluorescence characteristics, were identified by least-squares refinement in the −log[H⁺] range of 6.0-10.0. ¹H NMR spectra from the ligand in the complex showed separate peaks having two different rates of exchange with free ligand in the bulk solution besides a signal from the free and carboxylate-coordinated ligands. This indicates that the dinuclear complex, , consists of two different types of chelating ligands: μ-{OR}-type chelating ligands between metals to form the {Ln₂L₂}-type core structure and the bidentate ligands outside the {Ln₂L₂}-type core. This core structure is different from the An(IV)-SSA case (An(IV): tetravalent actinide), in which hydroxides play the role of forming the {An₂(OH)₂}-type core structure. TRLIFS measurement gave further information about the dynamics and molecular structures of the complexes.     

Syntheses and structural determination of new bis(9-tungstoarsenato)tris(dioxouranate(VI)) and its monooxovanadate(IV) derivative complexes

The [As₂W₁₈U₃O₇₄]¹²⁻ complex is formed by the “self-assembly” reaction of and (uranyl nitrate) ions in acidic media. The anion complex is isolated as the potassium salt and characterized by elemental analysis, IR, UV-Vis, and X-ray single crystal analysis. The complex contains an anion in which three ions are unsymmetrically sandwiched between two A-α-[AsW₉O₃₄]⁹⁻ groups leading to a structure of C_3v symmetry. Each uranium atom adopts pentagonal-bipyramidal coordination, achieved by three equatorial bonds to one [AsW₉O₃₄]⁹⁻and two bonds to the other. The [As₂W₁₈U₂V₂O₇₃]¹²⁻and also [As₂W₁₈U₃O₇₄]¹²⁻ complexes are formed also, by reaction of the [KAs₂W₁₈U₂O₇₂]¹³⁻ with VO²⁺ and ions in 1:1 mole ratio. The cyclic voltammogram of [As₂W₁₈U₂VO₇₃]¹²⁻ in acetate buffer (pH 4.7) shows a reversible one-electron redox process for V^IV/V couple at +0.396 (E_pc) and +0.432 V (E_pa).     

Luminescent metalloreceptors with pendant macrocyclic ionophore: Synthesis, characterization, electrochemistry and ion-binding study

Metalloreceptors containing ruthenium(II) bipyridine unit as fluorophore and pendant macrocyclic units as ionophore have been synthesized and their luminescence and electrochemical properties have been investigated. Ion-binding study of these fluoroionophore with the anions F⁻, Cl⁻, Br⁻, I⁻, , , , , CH₃COO⁻, and and cations Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Ba²⁺, Sr²⁺ Cd²⁺, Hg²⁺, Pb²⁺ and Cu²⁺, monitored by luminescence and ¹H NMR spectral changes, reveal strong interactions of and F⁻ for 2 and 3 and of Cu²⁺ only for 3. Luminescence titrations for 2 and 3 have been carried out to determine binding constants (K_s), and the calculated values are in the range 2.85 × 10² to 4.48 × 10⁴ M⁻¹. The ¹H NMR spectral changes for 2 and 3 with the addition of increasing concentration of F⁻ and exhibit substantial low-field shift of the CONH proton indicating its involvement in complex formation with the anions. The adduct of 2 and 3 have been isolated and characterized by ¹H and ³¹P NMR, mass and IR spectroscopy. The results are discussed in light of selectivity, structures of the anion bound complexes and their luminescence property.     

Dinuclear gold(III) pyrazolato complexes - Synthesis, structural characterization and transformation to their trinuclear gold(I) and gold(I/III) analogues

The reaction of AuCl₃py with Na(pz∗) (pz∗ = pyrazolato, or substituted pyrazolato anion) yields stable dinuclear [cis-Au^IIICl₂(μ-pz∗)]₂ complexes. In the presence of a base, the latter undergo reduction with concomitant transformation of the dinuclear -structure to trinuclear Au^I, Au^III (containing trans Au^IIICl₂-centres) and species.     

New applications of ruthenium solar cell sensitizers N3 and N719 as luminescence turn-on anion sensors

Optical sensing of F⁻, Cl⁻, Br⁻, I⁻, OAc⁻, , , and by cis-dithiocyanatobis(2,2′-bipyridyl-4,4′-dicarboxylic acid)ruthenium(II) (N3) and bis(tetrabutylammonium) cis-dithiocyanatobis(2,2′-bipyridine-4-COOH,4′-COO⁻)ruthenium(II) (N719) have been investigated in dimethyl sulfoxide (DMSO), by means of UV-Vis absorption and emission spectrophotometric titrations. Additions of F⁻, OAc⁻, and in DMSO solution caused obvious UV-Vis spectral changes with appearance of several isosbestic points, and remarkable emission enhancements along with large blue shifts in emission bands. The values of F⁻-induced emission intensity enhancement factor (emission quantum yield enhancement factor), I/I₀ (φ/φ₀), were found to be 40 (86) and 38 (58) for N3 and N719, respectively. No obvious spectral changes were observed upon addition of Cl⁻, Br⁻, I⁻, and in DMSO solutions. Luminescent F⁻ sensing in DMSO/H₂O (4:1, v/v) has also been demonstrated to be operative with a luminescence enhancement factor of 12, indicating that N3 is very potential for practical application as fluorescent anion sensor in aqueous solution. An interaction mechanism of anion-induced deprotonation of N3 and N719 was confirmed, and the deprotonation reaction equilibrium constants of N3 and N719 were derived as well.     

Synthesis, spectroscopy, computational evaluation and first X-ray structural characterization of a primary amine containing boronium ion

Stable (CF₃SO₂)₂N⁻, I⁻ and salts of the boronium ion [(tert-butylamine)(1-methylimidazole)BH₂]⁺ have been isolated and characterized. A single-crystal X-ray structure of the salt provides the first unambiguous proof for a boronium ion supported by a primary amine ligand.     

Alternating carrier models of asymmetric glucose transport violate the energy conservation laws

Alternating access transporters with high-affinity externally facing sites and low-affinity internal sites relate substrate transit directly to the unliganded asymmetric “carrier” (Cⁱ) distribution. When both bathing solutions contain equimolar concentrations of ligand, zero net flow of the substrate-carrier complex requires a higher proportion of unliganded low-affinity inside sites () and slower unliganded “free” carrier transit from inside to outside than in the reverse direction. However, asymmetric rates of unliganded carrier movement, k_ij, imply that an energy source, ΔG_carrier = RT ln (k_oi/k_io) = RT ln (Cⁱⁿ/C^out) = RT ln (), where R is the universal gas constant (8.314 Joules/M/K°), and T is the temperature, assumed here to be 300 K°, sustains the asymmetry. Without this invalid assumption, the constraints of carrier path cyclicity, combined with asymmetric ligand affinities and equimolarity at equilibrium, are irreconcilable, and any passive asymmetric uniporter or cotransporter model system, e.g., Na-glucose cotransporters, espousing this fundamental error is untenable. With glucose transport via GLUT1, the higher maximal rate and K_m of net ligand exit compared to net ligand entry is only properly simulated if ligand transit occurs by serial dissociation-association reactions between external high-affinity and internal low-affinity immobile sites. Faster intersite transit rates occur from lower-affinity sites than from higher-affinity sites and require no other energy source to maintain equilibrium. Similar constraints must apply to cotransport.     

Coordination versatility of 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane: Co(II) and Ni(II) complexes

The ligand 1,3-bis[3-(2-pyridyl)pyrazol-1-yl]propane (L⁸) has afforded six-coordinate monomeric and dimeric complexes [(L⁸)Co^II(H₂O)₂][ClO₄]₂ (1), [(L⁸)Ni^II(MeCN)₂][BPh₄]₂ (2), [(L⁸)Ni^II(O₂CMe)][BPh₄] (3), and . The crystal structures of 1, 2 · MeCN, 3, and 4 revealed that the ligand L⁸ is flexible enough to expand its coordinating ability by fine-tuning the angle between the chelating fragments and hence folds around cobalt(II)/nickel(II) centers to act as a tetradentate chelate, allowing additional coordination by two trans-H₂O, cis-MeCN, and a bidentate acetate affording examples of distorted octahedral , , and coordination. The angles between the two CoN₂/NiN₂ planes span a wide range 23.539(1)° (1), 76.934(8)° (2), and 69.874(14)° (3). In contrast, complex 4 is a bis-μ-1,3-acetato-bridged (syn-anti coordination mode) dicobalt(II) complex [Co?Co separation: 4.797(8) Å] in which L⁸ provides terminal bidentate pyridylpyrazole coordination to each cobalt(II) center. To our knowledge, this report provides first examples of such a coordination versatility of L⁸. Absorption spectral studies (MeCN solution) have been done for all the complexes. Complexes 1-3 are uniformly high-spin. Temperature-dependent (2-300 K) magnetic studies on 4 reveal weak ferromagnetic exchange coupling between two cobalt(II) (S = 3/2) ions. The best-fit parameters obtained are: Δ (axial splitting parameter) = −765(5) cm⁻¹, λ (spin-orbit coupling) = −120(3) cm⁻¹, k (orbital reduction factor) = 0.93, and J (magnetic exchange coupling constant) = +1.60(2) m⁻¹.     

Conductometric and voltammetric studies on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl2(L)(PPh3)2], where L: 2-(2′-pyridyl)quinoxaline

Conductometric investigation on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl₂(L)(PPh₃)₂] (A) (where PPh₃: triphenyl phosphine and L: 2-(2′-pyridyl)quinoxaline, C₁₃N₃H₉), in dimethylsulfoxide (DMSO) was performed at temperatures ranging from 25 to 50 °C. In addition, cyclic voltammograms of A were recorded on platinum working electrode in dichloromethane (DCM) and dimethylsulfoxide (DMSO) using n-tetrabutylammonium hexafluorophosphate (NBu₄PF₆) as supporting electrolyte at 25 °C. The molar conductivities (Λ) demonstrate that A behaves as uni-univalent electrolyte in DMSO over the whole temperature range. This behavior can be explained in terms of the replacement upon dissolution of chlorine and PPh₃ ligands by DMSO molecules, and consequently, the formation of the ion-pair [RuCl(L)(PPh₃)(DMSO)₂]Cl [B⁺Cl⁻] which is dissociated in some extent. The Λ values were analyzed by means of the Lee-Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λ^o) and the ion-pair association constants (K_A) of [B⁺Cl⁻]. The limiting ion conductivities for the B⁺ ion were evaluated using n-tetrabutylammonium chloride (NBu₄Cl) as “reference electrolyte”. The thermodynamic functions related with the ion association, such as Gibbs free energy , enthalpy , and entropy , were evaluated as well. The mobility of B⁺ was found to increase linearly with rising temperature and the consequent decrease of the viscosity (η) of DMSO. The K_A and values indicate that the association of [B⁺Cl⁻] increases to some extent with the rise of the temperature followed by the decrease of the dielectric constant (ε) of DMSO. The voltammetric experiments indicated that the couple Ru^3+/2+ is reversible and diffusion controlled in DCM and completely irreversible in DMSO.     

Interaction of gold(I) with thiosulfate-sulfite mixed ligand systems

The system was studied at 25 °C and at I = 0.1 M NaClO₄ using hydrodynamic voltammetry, gold potentiometry, UV-Vis spectrophotometry and Raman spectroscopy. The presence of two mixed-ligand species, Au(S₂O₃)(SO₃)³⁻ and , was detected from the Raman experiments and supported by the gold potentiometric experiments. The stepwise formation constant, log K_11r, for the reaction was found to be 1.1 (r = 1) and 4.8 (r = 2) from the hydrodynamic voltammetric experiments.     

Microwave-assisted solubilization and solution properties of hyperbranched polysaccharide

A water-insoluble hyperbranched β-d-glucan (TM3a), extracted from sclerotia of Pleurotus tuber-regium, was treated by microwave exposure to improve its solubility in water. This method led to complete dissolution of the TM3a polysaccharide in 0.02 wt % aqueous NaN₃. Various treatment periods were tested, and optimal conditions corresponded to 35 s at 765 W. The solution properties of TM3a in water were studied systematically by using size-exclusion chromatography combined with laser light scattering, viscometry, and dynamic light scattering at 25 °C. The dependences of intrinsic viscosity ([η]), radius of gyration (), and hydrodynamic radius (R_h) on weight average molecular weight (M_w) for TM3a in 0.02 wt % aqueous NaN₃ at 25 °C were found to be , , and in the M_w range from 8.20 × 10⁵ to 4.88 × 10⁶. The fractal dimension, ratio of , and the <r²>_o/M_w value of TM3a were calculated and discussed. The results indicated that TM3a existed in a sphere-like conformation in 0.02 wt % aqueous NaN₃. Furthermore, by using transmission electron microscopy, we observed directly the spherical molecules of TM3a. This work gave valuable information on improvement of solubility and chain conformation characterization of the water-insoluble polysaccharide in water.