Synthesis, characterization, and crystal structure of the Pd(phen)(bdt) complex. A DFT and TDDFT study of its ground electronic and excited states compared to those of analogous complexes

The synthesis and characterization of Pd(phen)(bdt) (1) (phen = 1,10-phenanthroline, bdt = 1,2-benzenedithiolate) is presented. 1 crystallizes in the monoclinic space group P2(1)/c, alpha = 11.281(4) A, b = 20.498(8) A, c = 8.374(3) A, beta = 90.234(8), V = 1936.5(13) A(3), Z = 4, and is isostructural with its previously reported related complexes. The ground and low lying excited electronic states in 1 and in the related complexes Pd(bpy)(bdt) (2), Pt(bpy)(bdt) (3), Pt(bpy)(mnt) (4), and Pt(bpy)(edt) (5) [where bpy = 2,2'-bipyridine, edt = ethylene-1,2-dithiolate, and mnt = maleonitriledithiolate] are studied using density functional theory techniques. The electronic properties of 1-5 are studied using the B3LYP functional. Optimized geometries are compared to experimentally observed structures. Time dependent density functional theory (TDDFT) is employed to investigate the excited singlet and triplet states. The calculated energies of the lowest singlet state and the lowest triplet state in all five complexes are in considerable agreement with experimental data. It is shown that variation of both metal and dithiolate-ligand going from 1 and 2 to 3, 4, and 5 has a substantial impact on the spectroscopic and excited-state properties, indicating at the same time the mixed metal/dithiolate character of the HOMO orbital. All the low-lying transitions are categorized as MMLL'CT transitions. The emissive state of all complexes is assigned as a triplet dithiolate/metal to diimine charge transfer with differences in the structures of the emissions resulting from differences in the pi dithiolate orbital of the mnt, bdt, and edt as well as from differences in metal.     

Electrochemical Studies of an Iron Porphyrin Immobilized on Nb2O5/SiO2 and Its Application for Simultaneous Determination of Dopamine and Ascorbic Acid Using Multivariate Calibration Methodology

This paper shows an application of a first generation porphyrin, FeTPPCl 5,10,25,20‐tetraphenylporphyrin iron(III) chloride (FeTPPCl or FeTPP⁺) immobilized on a inorganic matrix, SiO₂/Nb₂O₅ (niobium oxide grafted on silica gel surface, designated as SiNb) to the preparation of a carbon paste electrode (CPE). The carbon paste modified with a FeTPP⁺ immobilized on SiO₂/Nb₂O₅ (SiNb), designated as CPE/SiNb/FeTPP, was applied for simultaneous electrochemical determination of dopamine (DA) and ascorbic acid (AA). Because of the overlapping of the voltammetric peaks of DA and AA, the multivariate calibration methodology based on partial least square regression (PLSR) was proposed. The data pre‐treatment used in this process was mean centering and to choose the principal components number a cross validation procedure was used (leave‐one‐out). Five principal components were necessary to obtain the lowest PRESS (prediction residual error sum of squares). The statistics showed that this model explains approximately 95.2% of the variance from the data set. Using this model, high correlation between actual and predicted concentrations was observed, mainly for higher dopamine (maximum relative error of 8%) and ascorbic acid (maximum relative error of 10%) concentrations. For low analytes concentrations the relative error increases to 35% for AA. Considering the similarity of the voltammetric response of the analytes, the results obtained were satisfactory and showed the promissory capability of the CPE/SiNb/FeTPP coupled multivariate calibration methods for simultaneous voltammetric analysis of DA and AA.     

Influence of eicosapentaenoic acid, an omega-3 fatty acid, on ultraviolet-B generation of prostaglandin-E2 and proinflammatory cytokines interleukin-1 beta, tumor necrosis factor-alpha, interleukin-6 and interleukin-8 in human skin in vivo

Dietary omega-3 polyunsaturated fatty acids (omega-3 PUFA) reduce sunburn, an acute inflammatory response, in humans. We assessed whether this may be mediated by reduced ultraviolet-B (UV-B) induction of proinflammatory mediators tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1 beta, IL-6, IL-8 and prostaglandin (PG)E(2) in healthy skin. In a double-blind, randomized study, 28 humans received 4 g daily of 95% ethyl esters of eicosapentaenoic acid (EPA) or oleic acid (OA) orally for 3 months. Skin biopsies and suction blister fluid were taken from unexposed and UV-B-exposed skin and examined for mediator expression immunohistochemically and quantitatively by immunoassay; plasma levels were also assayed. The subjects taking EPA, but not OA, showed a significant rise in their minimal erythemal dose (MED) (data reported elsewhere). Before supplementation, irradiation with 3x MED UV-B increased blister fluid TNF-alpha, IL-6, IL-8 and PGE(2) at 16 h (all P < 0.001). No significant change occurred in baseline or UV-B-induced skin levels of cytokines after either supplement, whereas UV-B induction of PGE(2) was abolished after EPA but not OA. Immunohistochemical expression of the cytokines at baseline and after UV-B was unaltered by EPA and OA; circulating cytokine and PGE(2) levels were also unchanged. Hence, in healthy skin in vivo, there was no evidence that reduction of the sunburn response by EPA is mediated by the proinflammatory cytokines examined; abrogation of UV-B-generated PGE(2) may play a role.     

Electroanalytical Performance of (SiPy+Cl−/CuTsPc)5 LbL Film for Detecting Promethazine Hydrochloride

A (SiPy⁺Cl^?/CuTsPc)₅ layer‐by‐layer film was employed for the electroanalytical determination of promethazine hydrochloride in BR buffer pH 5.0 with peaks at 0.48 and 0.79 V. After optimisation of the square‐wave parameters (f=100 s^?1, a=40 mV and ΔE_s=2 mV), the peak at 0.79 V was used for quantification and a detection limit of 8.71×10^?9 mol L^?1 and a quantification limit of 9.31×10^?8 were calculated. The applicability of this procedure was tested on commercial formulations of promethazine hydrochloride by observing the stability, specificity, recovery and precision of the procedure in complex samples, without any preliminary treatment.     

Carbon ceramic electrodes modified with mixed oxides SiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> for determination of levofloxacin

The preparation of a carbon ceramic electrode modified with SnO₂ (CCE/SnO₂) using tin dibutyl diacetate as precursor was optimized by a 2³ factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si–O–Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO₂ provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO₂, indicating that SnO₂ when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10^?5 to 6.97×10^?4 mol L^?1 with quantification and detection limits of 3.80×10^?5 mol L^?1 (14.07 mg L^?1) and 1.13×10^?5 mol L^?1 (4.18 mg L^?1), respectively.     

Tuning copper-dioxygen reactivity and exogenous substrate oxidations via alterations in ligand electronics

Copper(I)-dioxygen adducts are important in biological and industrial processes. For the first time we explore the relationship between ligand electronics, CuI-O2 adduct formation and exogenous substrate reactivity. The copper(I) complexes [CuI(R-MePY2)]+ (1R, where R = Cl, H, MeO, Me2N) were prepared; where R-MePY2 are 4-pyridyl substituted bis[2-(2-pyridyl)ethyl]methylamine chelates. Both the redox potential of 1R (ranging from E1/2 = -270 mV for 1Cl to -440 mV for 1MeN vs FeCp2/FeCp2+) and nuCO of the CO adducts of 1R (ranging from 2093 cm-1 for 1Cl-CO to 2075 cm-1 for 1Me2N-CO) display modest but expected systematic shifts. Dioxygen readily reacts with 1H, 1MeO, and 1Me2N, forming the side-on peroxo-CuII2 complexes [{CuII(R-MePY2)}2(O2)]2+ (2R, also containing some bis-mu-oxo-CuIII2 isomer), but there is no reaction with 1Cl. Stopped-flow studies in dichloromethane show that the formation of 2Me2N from dioxygen and 1Me2N proceeds with a k = 8.2(6) x 104 M-2 s-1 (183 K, DeltaH = -20.3(6) kJ mol-1, DeltaS = -219(3) J mol-1 K-1). Solutions of 2R readily oxidize exogenous substrates (9,10-dihydroanthracene --> anthracene, tetrahydrofuran (THF) --> 2-hydroxytetrahydrofuran (THF-OH), N,N-dimethylaniline --> N-methylaniline and formaldehyde, benzyl alcohol --> benzaldehyde, benzhydrol --> benzophenone, and methanol --> formaldehyde), forming the bis-mu-hydroxo-CuII2 complexes [{CuII(R-MePY2)(OH)}2]2+ (3R). Product yields increase as the R-group is made more electron-donating, and in some cases are quantitative with 2Me2N. Pseudo-first-order rate constants for THF and methanol oxidation reactions demonstrate a remarkable R-group dependence, again favoring the strongest ligand donor (i.e., R = Me2N). For THF oxidation to THF-OH a nearly 1500-fold increase in reaction rate is observed (kobs = 2(1) x 10-5 s-1 for 2H to 3(1) x 10-2 s-1 for 2Me2N), while methanol oxidation to formaldehyde exhibits an approximately 2000-fold increase (kobs = 5(1) x 10-5 s-1 for 2H to 1(1) x 10-1 s-1 for 2Me2N).     

Electrochemical behavior of pyrroloquinoline quinone immobilized on silica gel modified with zirconium oxide

Pyrroloquinoline quinone (PQQ) was immobilized on the silica gel surface modified with zirconium oxide, designated as Si:Zr, by the carboxylic groups of the PQQ molecule and the zirconium oxide on the silica surface. The electrochemistry of PQQ immobilized on the Si:Zr matrix, incorporated in a carbon paste electrode, was evaluated using the cyclic voltammetry technique. The Si:Zr:PQQ-modified electrode showed a redox couple at E(m)=(E(pa1)+E(pc))/2=-0.150 V vs SCE at pH 7, close to that observed in aqueous solution, and another oxidation peak, E(pa2)=-0.100 V vs SCE. Studies in different pH solutions in the range of 3-7 showed that the first oxidation peak, E(pa1), is highly dependent on the solution pH shifting from to -0.175 to 0.100 V vs SCE, while E(pa2) remains practically constant at 0.100 V as the pH decreases from 7 to 3. The immobilized PQQ electrode presented the property to electrocatalyze the NADH at 150 mV vs SCE. The effect of addition of Ca(2+) ions on the electrode electroactivity for the NADH oxidation was also verified. Different from that observed for the PQQ immobilized on other electrode materials, the Ca(2+) ions did not influence the electrocatalytical response; however, the electrode stability was considerably improved in the presence of Ca(2+) ions, indicating that the matrix surface has a great influence on the electrochemical behavior of PQQ.     

1-Ethyl-1H-3-nitrobenzopyrano[4,3,2-cd]isoindole: a novel heterocyclic ring system bearing an unusually labile deuterium-exchangeable aromatic proton

The ease of deuterium exchange of the aromatic H2 of the novel heterocycle 1-ethyl-1H-3-nitrobenzopyrano[4,3,2-cd]isoindole was studied by NMR and theoretical calculations.     

Copper(I)-dioxygen reactivity of [(L)Cu(I)](+) (L = tris(2-pyridylmethyl)amine): kinetic/thermodynamic and spectroscopic studies concerning the formation of Cu-O2 and Cu2-O2 adducts as a function of solvent medium and 4-pyridyl ligand substituent variations

The kinetic and thermodynamic behavior of O(2)-binding to Cu(I) complexes can provide fundamental understanding of copper(I)/dioxygen chemistry, which is of interest in chemical and biological systems. Here we report stopped-flow kinetic investigations of the oxygenation reactions of a series of tetradentate copper(I) complexes [(L(R))Cu(I)(MeCN)](+) (1(R), R=H, Me, tBu, MeO, Me(2)N) in propionitrile (EtCN), tetrahydrofuran (THF), and acetone. The syntheses of 4-pyridyl substituted tris(2-pyridylmethyl)amine ligands (L(R)) and copper(I) complexes are detailed. Variations of ligand electronic properties are manifested in the electrochemistry of 1(R) and nu(CO) of [(L(R))Cu(I)-CO](+) complexes. The kinetic studies in EtCN and THF show that the O(2)-reactions of 1(R) follow the reaction mechanism established for oxygenation of 1(H) in EtCN (J. Am. Chem. Soc. 1993, 115, 9506), involving reversible formation (k(1)/k(-1)) of [(L(R))Cu(II)(O(2-))](+) (2(R)), which further reacts (k(2)/k(-2)) with 1(R) to form the 2:1 Cu(2)O(2) complex [[(L(R))Cu(II)](2)(O(2)(2-))](2+) (3(R)). In EtCN, the rate constants for formation of 2(R) (k(1)) are not dramatically affected by the ligand electronic variations. For R = Me and tBu, the kinetic and thermodynamic parameters are very similar to those of the parent complex (1(H)); e.g., k(1) is in the range 1.2 x 10(4) to 3.1 x 10(4) M(-1) s(-1) at 183 K. With the stronger donors R = MeO and Me(2)N, more significant effects were observed, with the expected increase in thermodynamic stability of resultant 2(R) and 3(R) complexes, and decreased dissociation rates. The modest ligand electronic effects manifested in EtCN are due to the competitive binding of solvent and dioxygen to the copper centers. In THF, a weakly coordinating solvent, the formation rate for 2(H) is much faster (>/=100 times) than that in EtCN, and the thermodynamic stabilities of both the 1:1 (K(1)) and 2:1 (beta = K(1)K(2)) copper-dioxygen species are much higher than those in EtCN (e.g., for 2(H), deltaH(o) (K(1))=-41 kJ mol(-1) in THF versus -29.8 kJ mol(-1) in EtCN; for 3(H), deltaH(o) (beta)=-94 kJ mol(-1) in THF versus -77 kJ mol(-1) in EtCN). In addition, a more significant ligand electronic effect is seen for the oxygenation reactions of 1(MeO) in THF compared to that in EtCN; the thermal stability of superoxo- and peroxocopper complexes are considerably enhanced using L(MeO) compared to L(H). In acetone as solvent, a different reaction mechanism involving dimeric copper(I) species [(L(R))(2)Cu(I)(2)](2+) is proposed for the oxygenation reactions, supported by kinetic analyses, electrical conductivity measurements, and variable-temperature NMR spectroscopic studies. The present study is the first systematic study investigating both solvent medium and ligand electronic effects in reactions forming copper-dioxygen adducts.