Complex formation between gadolinium(III) porphyrins and some nucleic bases or their nucleoside derivatives in aqueous solutions

Summary The mutual interactions of Gd(III)tetraphenylporphyrin (GdTPP), Gd(III)tetramethylpyridylporphyrin (GdTMePyP), and the free base tetramethylpyridylporphyrin (H₂ TMePyP) with some nucleic bases (adenine, thymine, uracil, and cytosine) and their N-glycoside derivatives (adenosine, thymidine, uridine, and cytidine) have been studied by spectrophotometric titration in mixed methanol-ammonia-water solutions. It has been found that tetramethylpyridylporphyrin and its gadolinium complex form 1:1 complexes with nucleic bases and their nucleoside derivatives. The equilibrium constants were estimated using curve fitting procedures. The interactions are stronger for nucleoside derivatives than for nucleic bases. They are also stronger for metallated than for non-metallated porphyrins.

---

Komplexbildung zwischen Gadolinium(III)porphyrinen und einigen Nucleinbasen oder ihren Nucleosidderivaten in wäßrigen Lösungen

Zusammenfassung Die Wechselwirkungen von Gd(III)tetraphenylporphyrin (GdTPP), Gd(III)-tetramethylpyridylprophyrin (GdMePyP) und der freien Base Tetramethylpyridylporphyrin (H₂ TMePyP) mit einigen Nucleinbasen (Adenin, Thymin, Uracil, Cytosin) und ihren N-glycosidierten Derivaten (Adenosin, Thymidin, Uridin, Cytidin) wurden in Methanol-Ammoniak-Wasser — Mischungen mittels spektrophotometrischer Titration untersucht. Tetramethylpyridylporphyrin und sein Gadoliniumkpomplex bilden 1:1-Komplexe mit Nucleinbasen und ihren Nucleosidderivaten. Die Gleichgewichtskonstanten wurden übercurve-fitting - Algorithmen bestimmt. Die Wechselwirkungen sind für Nucleosidderivate stärker als für Nucleinbasen und für metallierte Porphyrine stärker als für nichtmetallierte.

     

Synthesis and Langmuir-film formation of new dendritic DTPA-derived gadolinium(III) complexes

A series of dendritic DTPA-derived ligands and their corresponding gadolinium(III) complexes have been prepared and their spreading behaviour at the air-water interface has been investigated. The results show that these amphiphiles have the prerequisite qualities to form stable and reversible Langmuir monolayers opening the road to novel magnetic organic films.     

Complex formation equilibria between aluminum(III), gadolinium(III) and yttrium(III) ions and some fluoroquinolone ligands. Potentiometric and spectroscopic study

Complex formation equilibria of aluminum(III), gadolinium(III), and yttrium(III) ions with the fluoroquinolone antibacterials moxifloxacin, ofloxacin, fleroxacin, lomefloxacin, levofloxacin, and ciprofloxacin were studied in aqueous solution by potentiometric and spectroscopic methods. The identity and stability of metal–fluoroquinolone complexes were determined by analyzing potentiometric titration curves (310 K, μ = 0.15 M NaCl, pH range = 2–11, C_L/C_M = 1?:?1 to 3?:?1, C_M = 1.0 mM) with the aid of Hyperquad2006 program. The main species formed in the system may be formulated as M_pH_qL_r (p = 1, q = ?2 to 2, r = 1–3, L = fluoroquinolone anion, logarithm of overall stability constant, log β_p,q,r = in the range ca. ?10 to 45). The stability of complexes is mostly influenced by metal ion properties (ionization potential, ionic radius) indicating partial ionic character of the coordination bond. The complexes were also characterized by spectroscopic measurements: spectrofluorimetry, ¹H-NMR, and ESI-MS. Fluorimetric data were evaluated with the aid of HypSpec2014 and indicated the formation of ML_r (r = 1–3) complexes with cumulative conditional stability constants significantly lower than the thermodynamic ones. NMR and MS data corroborate potentiometrically determined speciation. Calculated plasma mobilizing capacity of the ligands generally follows the order levofloxacin > moxifloxacin > ciprofloxacin at concentration levels of the ligands higher or equal to ca. 10^?4 M.     

Structure and magnetic properties of homobinuclear gadolinium (III) complex of isonicotinoyl hydrazone

The crystal structure of [Gd₂(μ-L)₃(H₂O)₂]1.5(NO₃)1.5 (OH)5H₂O (where L is union of N, N-Diisonicotinoyl-2-hydroxy-5-methyl-isophthalaldehyde dihydrazone) has been determined by X-ray diffraction method. The complex crystallizes in the monoclinic system, space group P2₁/c with a=1.6654(3), b=1.6904(3), c=2.8039(6) nm, β=91.30(3), final R factor is 6.3%. The structure consists of [Gd₂(μ-L)₃(H₂O)₂]³⁺ cation, one and a half nitrate and 1.5 hydroxyl anions and five water molecules. Within dinuclear cation, Gd(III)—Gd(III) is bridged by oxygen and nitrogen atoms of the three ligands, resulting in Gd? Gd distance of 0.36353(2) nm. Gd(III) exhibits a distorted 1333 stack coordination environment. Magnetic susceptibility measurements in the temperature range 300–4 K revealed the occurrence of weak antiferromagnetic exchange interaction between two Gd(III) ions with a J value of—0.22, and g of 1.93.     

Post electron-beam irradiation oxidation of orthopaedic Ultra-High Molecular Weight Polyethylene (UHMWPE) stabilized with vitamin E

Ultra-High Molecular Weight Polyethylene (UHMWPE) has been the material of choice for load-bearing articular components used in total joint arthroplasty in the past 30 years. However, the durability of the whole implant has often been compromised by oxidation of UHMWPE components. Since the use of a suitable, biocompatible stabilizer would minimize this inconvenience, the possibility to use vitamin E has been introduced.In the present work, medical grade UHMWPE was blended with 1.1, 2.3 and 11 mmol/l of vitamin E and consolidated by compression moulding. Small blocks of reference and of vitamin E-blended UHMWPE were then electron-beam irradiated at 30, 60 and 90 kGy, both in vacuum and in air. FTIR spectroscopy was used to monitor changes in both the polymer and the additive. Thin sections of irradiated virgin and vitamin E-blended UHMWPE were aged in air, at room temperature and in the dark and the kinetics of oxidation followed by FTIR. The reaction between vitamin E and macro-alkyl radicals or unlikely with peroxy radicals has been demonstrated and a correlation between the decrease of macroradicals and the stabilization effect of vitamin E has been shown.     

Luminescent Au(III) organometallic complex of N-confused tetraphenylporphyrin

An organometallic Au(iii) complex of N-confused tetraphenylporphyrin has been synthesized and its electrochemical and photophysical properties investigated; unique emission is observed in solution at ambient temperature.     

A gadolinium(III) complex: synthesis,structure, photophysical profile and its role in the degradation of nitroaromatics

The synthesis and structural characterization of a gadolinium(III) complex with phenanthroline and thiocyanate ligands have been accomplished. The X-ray crystal structure reveals that Gd(III) in a slightly distorted square anti-prism coordinated with four thiocyanate ions and two phenanthroline molecules; one phenanthroline is protonated which compensates the charge of Gd(III) center. The crystal structure shows chemically significant non-covalent interactions like hydrogen bonding involving the thiocyanate ligand and π–π interactions between uncoordinated phenanthrolinium and coordinated phen. Investigation on the intermolecular interactions and crystal packing via Hirshfeld surface analysis reveals that close contacts are mainly associated with weak interactions. The fingerprint plots demonstrate that these weak interactions are important for crystal packing. The Gd(III) complex shows photophysical activity. The compound is capable of degrading toxic pollutants like nitroaromatics and may have far reaching consequences for cleaning these toxic pollutants from industrial effluents.     

Complexation of gadolinium(III) ions on top of nanometre-sized magnetoliposomes

The complex of diethylenetriaminepentaacetate (DTPA) with the paramagnetic gadolinium ion [Gd(III)] is a well-known blood pool contrast agent for magnetic resonance imaging (MRI). To obtain MRI pictures from other anatomical structures, for instance from tissues containing cells with phagocytic activity, larger colloidal complexes have to be constructed. Therefore, in view of modifying the physiological behaviour, the DTPA chelate was first hydrophobized by covalently linking it to phosphatidylethanolamine (PE), and the resulting conjugate was then incorporated into nanometre-sized, sonicated phospholipid vesicles. Qualitative information on the affinity of the PE–DTPA derivative for Gd(III) ions was derived from competition experiments using the dye Arsenazo. Furthermore, it was found that only the membranotropic adducts residing in the outer shell of the vesicle bilayer are accessible to the lanthanide ion. The vesicular particulate was also used as a vehicle to transport PE–DTPA into the coating of so-called magnetoliposomes which consist of nanometre-sized iron oxide cores onto which a phospholipid bilayer is strongly chemisorbed. After loading the resulting structures with Gd(III), this new type of magnetoliposome may offer unique potentialities as a novel bi-label MRI contrast medium.     

A CIDEP and fluorescence study of the oxidation of vitamin E: The vitamin E radical cation

The photochemical and thermal oxidations of vitamin E in trifluoroacetic acid were investigated by the combination of electron spin resonance, chemically induced dynamic electron polarization, and fluorescence techniques. Two independent thermal pathways led to the formation of the vitamin E radical cation in which one of the paths involved the intermediate neutral semiquinone radical. Photo-oxidation, however, did not involve the neutral radicals. The fluorescence spectra of both the neutral and the charged forms of the vitamin E radicals are reported here for the first time. Some model charge transfer reactions involving the vitamin E radical cation were reported.     

Novel phosphoranido complex of rhodium(III) tetraphenylporphyrin. Synthesis and characterization

A novel phosphoranido complex of rhodium(III) porphyrin was prepared by the reaction of a lithium phosphoranide, generated from a P-H phosphorane bearing two 8-oxy-1-naphthyl groups, with (TPP)RhCl (TPP = dianion of 5,10,15,20-tetraphenylporphyrin). The crystal structure of the complex was determined by X-ray structural analysis.     

Preparation, spectroscopic and high field NMR relaxometry studies of gadolinium(III) complexes with the asymmetric tetraamine 1,4,7,11-tetraazaundecane

The reaction of Gd(III) with asymmetric tetramine 1,4,7,11-tetraazaundecane (2,2,3-tet, L¹) ligand has been studied via NMR spectroscopy. The ligand proton longitudinal relaxation rates (R₁) have been used to estimate the distances of these protons from the Gd(III) center, in Gd(III)–L¹ reaction solutions, in H₂O/D₂O 5/1 mixtures.Two Gd(III) complexes [Gd(III)(L¹)(NH₃)(H₂O)₄](CH₃COO)₃·2H₂O (1) and [Gd(III)(L¹)(NH₃)(H₂O)₂]Cl₃·EtOH (2) have been isolated and characterized by elemental analyses, TGA, IR, NMR and relaxometry measurements. The NMR relaxation measurements of 2 in aqueous solutions have been performed, under various temperature or concentration conditions, and compared with those of the commercial contrast agents Gd(III)–DTPA and Gd(III)–DTPA-BMA. It has also been studied the influence of (i) the Gd(III) inner-sphere water molecule number (q) alteration and (ii) the steric constraint enhancement on the metal site, over the relaxation rate values of the parent aqueous solution of Gd(III)–2,2,3-tet, and of the aqueous solutions of 2.     

Synthesis of a new tricyclic tetraazatriacetic acid as ligand for gadolinium(III)

Polyazapolycarboxylic acids are known to be efficient ligands for the development of gadolinium-based contrast agents used in magnetic resonance imaging (MRI). Given that rigidification of the ligand structure seems to be an important structural parameter to increase the relaxivity of the corresponding gadolinium complex, we have synthesized a new tricyclic tetraazatriacetate ligand from commercially available trans-2-aminocyclohexanol. In the synthetic routes described here, the 2-nitrobenzenesulfonamide chemistry was used to selectively functionalize the polyamine precursors.     

Photochemical reaction of gadolinium(III) tetraphenylporphyrin in toluene solution containing an electron acceptor or donor

In this paper we have studied by absorption spectroscopy the course of the steady state photolysis of gadolinium(III) complex with 5,10,15,20-tetraphenylporphyrin. The result has been compared with the photolysis of free base tetraphenylporphyrin. Irradiation of GdTPP(acac) and H₂TPP (H₂TPP ≡ tetraphenylporphyrin; Hacac ≡ acetylacetone) with visible light in the presence of triethylamine as an electron donor, leads to their photoreduction. Formation of the gadolinium tetraphenylchlorin complex and tetraphenylchlorin is observed. The process of irradiation in the presence of CCI₄ as an electron acceptor has different pathways for GdTPP(acac) and H₂TPP. The gadolinium complex is mono oxidized, giving rise to the π⁺ radical cation while, for unmetallated porphyrin, dication H₄(TPP)²⁺ formation is observed.     

Flow injection spectrophotometric determination of vitamin E in pharmaceuticals,milk powder and blood serum using potassium ferricyanide-Fe(Ⅲ) detection system

<正>A simple and sensitive flow injection spectrophotometric method is reported for the determination of vitamin E using potassium ferricyanide-Fe(Ⅲ) detection system.In the presence of vitamin E,Fe(Ⅲ)/ferricyanide reduces.The in situ reduced ions are then reacted with unreduced portion of ferricyanide/Fe(Ⅲ) to make soluble Prussian blue,which is monitored at absorption wavelength of 735 nm.Linear calibration graph was obtained in the concentration range of 0.1-40μg mL~(-1).The relative standard deviations (n=4) were in the range of 1.1-3.6%,with limits of detection(3 s blank) of 0.04μg mL~(-1).The proposed method allowed 12 injections h~(-1).The method is applied to determine vitamin E in pharmaceuticals,infant milk and blood serum samples using hexane extraction with the recoveries in the range of 93±3 to 97.5±4%.The method is validated using certified reference materials SRM 968c for blood serum samples.     

On the complex formation equilibria between iron (III) and sulfate ions

The equilibria have been investigated at 25 degrees C in 3 M NaClO4 using potentiometry, glass and redox Fe3+/Fe2+ half-cells, and UV optical absorptiometry. The concentration of the reagents was chosen in the intervals: 10(-4) < or = [Fe(III)] < or = 5.10(-3) M, 0.01 < or = [SO4(2-)]tot < or = 0.65 M. The value of [H+] was kept at 0.1 M or more to reduce the hydrolysis of the Fe3+ ion to less than 1%. Auxiliary constants, corresponding to the formation of Fe(II)-sulfate complexes and to the association of H+ with SO4(2-) ions, were taken from previous determinations. The experimental data could be explained with the equilibria [formula: see text] Equilibrium constants at infinite dilution, log beta 101 degrees = 3.82 +/- 0.17, log beta 102 degrees = 5.75 +/- 0.17 and log beta 111 degrees = 3.68 +/- 0.35, have been evaluated by applying the specific interaction theory.     

Composition of a mixed-ligand gadolinium(III) complex in fluoride-dimethylformamide electrolyte

The gadolinium(III) complex formed in a fluoride-dimethylformamide (DMF) electrolyte was studied by linear-sweep voltammetry and IR spectroscopy. The composition of the mixed-ligand complex formed was found to correspond to the component ratios Gd: DMF: F = 1: 3: 4. It has been found that the coordination link in the complex is via two oxygen atoms and one nitrogen atom of dimethylformamide and involves four fluoride ions.     

Simultaneous assay of serum vitamin A and vitamin E by high performance liquid chromatography using time-switched UV and fluorimetric detectors

An HPLC method utilizing a UV and a fluorimetric detector linked in series is described. By use of a simple integrator-controlled time-switched relay, analysis of serum vitamin A and E is accomplished on the same chromatogram and at optimum sensitivity for each detector. A single internal standard (retinyl acetate) monitored only by the UV detector permits measurement of both vitamins over a wide linear range. Precision of the assays is satisfactory, both on a within-day and on a day-to-day basis. Recoveries of both vitamins are virtually 100% whilst sensitivity is 2 μg/L (retinol) and 0.05 mg/L (α-tocopherol).     

Kinetics and mechanism of the complex formation between oxalatopentaamminecobalt(III) and aluminium(III) and gallium(III); a comparative study

Summary The reversible complex formation between oxalatopentaammine cobalt(III), aluminium(III) and gallium(III) was investigated by the stopped flow technique at 30 ± 0.1 °C and I = 1.0 mol dm^–3. The reactivity sequence: Ga^III > Al^III is observed, however, the major path for gallium(III) was (NH3)₅CoC₂O₄H²⁺ + GaOH²⁺ (NH₃)₅CoC₂O₄-Ga⁴⁺ + H₂O. The formation and dissociation rate constants of the binuclear species have been compared with the analogous data for iron(III) and nickel(II) reported earlier. The results reflect the fact that the half-bonded exalato moiety of (NH₃)₅CoC₂O _inf4 ^p+ acts as a chelating agent for the metal ions.Author to whom all correspondence should be directed.