Synthesis, characterization, and DNA-binding properties of the Ln(III) complexes with 6-hydroxy chromone-3-carbaldehyde-(2'-hydroxy) benzoyl hydrazone

A new ligand, 6-hydroxy chromone-3-carbaldehyde-(2'-hydroxy) benzoyl hydrazone (L), was prepared by condensation of 6-hydroxy-3-carbaldehyde chromone (CDC) with 2-hydroxy benzoyl hydrazine. Its four rare earth complexes have been synthesized and characterized on the basis of elemental analyses, molar conductivities, mass spectra, 1H NMR, thermogravimetry/differential thermal analysis (TG-DTA), UV-vis spectra, fluorescence spectra, and IR spectra. The general formula of the complexes is [LnL2.(NO3)2].NO3 [Ln=La(1), Sm(2), Dy(3), Eu(4)]. Spectrometric titration, ethidium bromide displacement experiments, and viscosity measurements indicate that Eu(III) complex and ligand, especially the Eu(III) complex, strongly bind with calf-thymus DNA, presumably via an intercalation mechanism. The intrinsic binding constants of Eu(III) complex and ligand with DNA were 3.55 x 10(6) and 1.33 x 10(6)M(-1) through fluorescence titration data, respectively. In addition, the suppression ratio for O2-* and OH* of the ligand and its complexes was studied by spectrophotometric methods. The experimental results show that La (1), Sm (2), and Eu (4) complexes are better effective inhibitor for OH* than that of mannitol. It indicates that the complexes have the activity to suppress O2-* and OH* and exhibit more effective antioxidants than ligand alone.     

Antioxidation and DNA-Binding Properties of Binuclear Lanthanide(III) Complexes with a Schiff Base Ligand Derived from 8-Hydroxyquinoline-7-carboxaldehyde and Benzoylhydrazine

8-Hydroxyquinoline-7-carboxaldehyde (8-HQ-7-CA), Schiff-base ligand 8-hydroxyquinoline-7-carboxaldehyde benzoylhydrazone, and binuclear complexes [LnL(NO(3) )(H(2) O)(2) ](2) were prepared from the ligand and equivalent molar amounts of Ln(NO(3) )?6 H(2) O (Ln=La(3+) , Nd(3+) , Sm(3+) , Eu(3+) , Gd(3+) , Dy(3+) , Ho(3+) , Er(3+) , Yb(3+) , resp.). Ligand acts as dibasic tetradentates, binding to Ln(III) through the phenolate O-atom, N-atom of quinolinato unit, and C?N and ?O?C?N? groups of the benzoylhydrazine side chain. Dimerization of this monomeric unit occurs through the phenolate O-atoms leading to a central four-membered (LnO)(2) ring. Ligand and all of the Ln(III) complexes can strongly bind to CT-DNA through intercalation with the binding constants at 10(5) -10(6) M(-1) . Moreover, ligand and all of the Ln(III) complexes have strong abilities of scavenging effects for hydroxyl (HO(.) ) radicals. Both the antioxidation and DNA-binding properties of Ln(III) complexes are much better than that of ligand.     

Crystal structures, DNA-binding studies and antioxidant activities of the Ln(III) complexes with 7-methoxychromone-3-carbaldehyde-isonicotinoyl hydrazone

The neutral mononuclear Ln(III) complexes (Ln = La, Sm) with 7-methoxychrom-one-3-carbaldehyde-isonicotinoyl hydrazone ligand (L) have been synthesized, characterized and investigated their interactions with calf-thymus DNA. The results show that the binding affinity of the La(III) complex is stronger than that of the Sm(III) complex and that of the ligand (L). Furthermore, the antioxidant activities of the ligand (L) and its Ln(III) complexes (Ln = La, Sm) were studied in detail.     

Study on synthesis, structure, and DNA-binding of lanthanide complexes with 2-carboxylbenzaldehyde thiosemicarbazone

2-Carboxylbenzaldehyde thiosemicarbazone (HL), and its three lanthanide (III) complexes, LnL(3) x 4H(2)O [Ln(III)=La, Sm, Eu], have been synthesized in water. The complexes were characterized by elemental analyses, molar conductivity and IR spectra. The crystal structure of [Sm(2)L(6)(CH(3)OH)(4)] x 7.5CH(3)OH x 0.5H(2)O obtained from methanol solution was determined by X-ray diffraction analysis, crystallized in the triclinic system, space group P-1, Z=1, a=12.217 (2)A, b=14.706 (2)A, c=15.035 (2)A, alpha=111.84(1) degrees , beta=103.47(1) degrees , gamma=104.24(1) degrees , R(1)=0.0290. It has symmetrical (mu-OCO)(2), (mu-O)(2) and disamarium(III) units. The coordination geometry of each Sm(III) ion is a distorted tetradecahedron with nine oxygen atoms. In addition, the DNA-binding properties of the ligand and its complexes have been investigated by absorption, fluorescence, and viscosity measurements. The experimental results indicate that the ligand and the Sm-complex can bind to DNA, but the other two complexes cannot; the binding affinity of the Sm-complex is higher than that of the ligand and the intrinsic binding constant K(b) of the complex is 3.22 x 10(5)M(-1).     

Synthesis, characterization, cytotoxic activities, and DNA-binding properties of the La(III) complex with Naringenin Schiff-base

A new Naringenin Schiff-base ligand (H3L) and its complex, [La(H2L)2(NO3).3H2O], have been synthesized and characterized on the basis of elemental analyses, molar conductivities, mass spectra, 1H NMR, thermogravimetry/differential thermal analysis (TG-DTA), UV spectra, and IR spectra. Spectrometric titrations, ethidium bromide displacement experiments, and viscosity measurements indicate that the two compounds, especially the La(III) complex, strongly bind with calf-thymus DNA, presumably via an intercalation mechanism. The intrinsic binding constants of the La(III) complex and ligand with DNA were 1.83 x 10(7) and 9.46 x 10(5) M(-1), respectively. Comparative cytotoxic activities of the La(III) complex and ligand were also determined by MTT [3-(4,5-dimethyl-2-thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide] and SRB (sulforhodamine B) methods. The results showed that the La(III) complex had significant cytotoxic activity against the tested cells.     

Synthesis,characterization and cytotoxic/cytostatic activity of La(III) and Dy(III) complexes

New La(III) and Dy(III) complexes of deprotonated 4-hydroxy-3[1-(4-nitrophenyl)-3-oxobutyl]-2H-1-benzopyran-2-one (Acenocoumarol) were synthesized and characterized using FT-IR, FT-Raman, ¹H NMR spectra, and elemental analyses. The ligand and its lanthanide(III) complexes were tested for their cytotoxic/cytostatic activity against two tumor cell lines and peritoneal mouse macrophages. The La(III) and Dy(III) complexes exhibit good activity against melanoma B16 and fibrosarcoma L929 and they are stronger inhibitors of tumor cell proliferation compared to the ligand without influencing normal cell viability and NO release by mouse peritoneal macrophages.     

The superoxide dismutase activities of two higher valent manganese complexes, MnIV desferrioxamine and MnIII-cyclam.

A green manganese desferrioxamine complex is rapidly formed at room temperature upon stirring freshly precipitated manganese dioxide in a solution of the ligand. Spectral studies and low-temperature ESR indicate that this compound, which has been previously described as a manganese(III) complex, is better characterized as containing tetravalent manganese. The complex appears to form oligomers in solution. The extinction coefficient at 635 nm is 137 +/- 6 M-1 cm-1 (per manganese) at pH 7.8 and 88 +/- 4 M-1 s-1 at pH 6.6 after purification by chromatography. The superoxide dismutase activity was measured and compared to that of mononuclear manganese(III) 1,4,8,11-tetraazacyclodecane (cyclam). The catalytic rate constants for superoxide dismutase activity are 1.7 x 10(6) M-1 s-1 and 2.9 x 10(6) M-1 s-1 for the desferrioxamine and the cyclam complexes, respectively.     

Novel procedures for preparing 99mTc(III) complexes with tetradentate/monodentate coordination of varying lipophilicity and adaptation to 188Re analogues

Improved methods are presented for the preparation of 99mTc and 188Re mixed-ligand complexes with tetradentate and monodentate ligands of the general formula [MIII(Lm)(Ln)] (M = Tc, Re; Lm = NS3 or NS3COOH; Ln = isocyanide or phosphine). To avoid the undesired formation of reduced-hydrolyzed species of both metals, the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand 2,2',2' '-nitrilotris(ethanethiol) (NS3) or its carboxyl derivative NS3COOH (a) and the monodentate phosphine ligands (triphenylphosphine L1, dimethylphenylphosphine L2) or isocyanides (tert-butyl isonitrile L3, methoxyisobutyl isonitrile L4, 4-isocyanomethylbenzoic acid-L-arginine L5, 4-isocyanomethylbenzoic acid-L-arginyl-L-arginine L6, 4-isocyanomethylbenzoic acid-neurotensin(8-13) L7) to the so-called '4+1' complex. Copper(I) isocyanide complexes are used for preparing the '4+1' complexes. That facilitates storage stability and allows kit formulations, and, moreover, enables the formation of 188Re complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed, and that results in high specific activity labeling of interesting molecules. The lipophilicity of complexes can be controlled by introducing a carboxyl group into the tetradentate ligand and/or derivatization of the monodentate ligands. Furthermore, the carboxyl group enables the conjugation of biomolecules. As an example, the neurotensin derivative CN-NT(8-13) was prepared and labeled with 99mTc according to the '4+1' approach, and its behavior in vivo was studied.     

Synthesis, characterization and biological activity of complexes of lanthanum(III) with 2-(1'-phenyl- 2'-carboxyl-3'-aza-n-butyl)-1,10-phenanthroline and 2-(1'-p-phenol-2'-carboxyl-3'-aza-n-butyl)-1,10-phenanthroline

Two novel ligands 2-(1'-phenyl-2'-carboxyl-3'-aza-n-butyl)-1,10-phenanthroline (L1) and 2-(1'-p-phenol-2'-carboxyl-3'-aza-butyl)-1,10-phenanthroline (L2), and their La(III) complexes of La(III)L1, La(III)(L1)(2), La(III)L2, and La(III)(L2)(2), were synthesized and characterized by (1)H NMR, elemental analysis, IR, thermal analysis and conductance measurement. All complexes have been assayed for anticancer activity in vitro against HL-60 (human leukocytoma) cells, PC-3MIE8 (human prostate carcinoma) cells, BGC-823 (human stomach carcinoma) cells, MDA-MB-435 (human galactophore carcinoma) cells, Bel-7402 (human liver carcinoma) cells, and HeLa (human cervix carcinoma) cells. Results showed that the two complexes La(III)L1 and La(III)(L1)(2) exhibited good cytotoxic activity against different cell lines in general; and La(III)(L1)(2) is more effective than cisplatin against all six cell lines. DNA-binding studies indicated that, besides the intercalation, the complexes bind to DNA by the other interaction(s).     

Synthesis,density functional theory calculations and luminescence of lanthanide complexes with 2,6‐bis[(3‐methoxybenzylidene)hydrazinocarbonyl] pyridine Schiff base ligand

A pyridine‐diacylhydrazone Schiff base ligand, L = 2,6‐bis[(3‐methoxy benzylidene)hydrazinocarbonyl]pyridine was prepared and characterized by single crystal X‐ray diffraction. Lanthanide complexes, Ln–L, {[LnL(NO₃)₂]NO₃.xH₂O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Er)} were prepared and characterized by elemental analysis, molar conductance, thermal analysis (TGA/DTGA), mass spectrometry (MS), Fourier transform infra‐red (FT‐IR) and nuclear magnetic resonance (NMR) spectroscopy. Ln–L complexes are isostructural with four binding sites provided by two nitro groups along with four coordination sites for L. Density functional theory (DFT) calculations on L and its cationic [LnL(NO₃)₂]⁺ complexes were carried out at the B3LYP/6–31G(d) level of theory. The FT‐IR vibrational wavenumbers were computed and compared with the experimentally values. The luminescence investigations of L and Ln–L indicated that Tb–L and Eu–L complexes showed the characteristic luminescence of Tb(III) and Eu(III) ions. Ln–L complexes show higher antioxidant activity than the parent L ligand.     

Spectroscopy, cytotoxicity and DNA-binding of the lanthanum(III) complex of an L-valine derivative of 1,10-phenanthroline

The interaction of the lanthanum(III) La(III)-L (L=N,N'-bis-(1-carboxy-2-methylpropyl)-1,10-phenanthroline-2,9-dimethanamine) complex with calf thymus DNA was studied by electronic spectra, fluorescence spectra and circular dichroic spectra. The La(III)-L complex was assayed for antitumor activity in vitro against the HL-60 (the human leucocytoma) cells, HCT-8 (the human coloadenocarcinoma) cells, BGC-823 (the human carcinoma of stomach) cells, Bel-7402 (the human liver carcinoma) cells and KB (the human nasopharyngeal carcinoma) cells. The results show that the La(III)-L complex has activity against HL-60 cells, Bel-7402 cells and KB cells. Moreover, it is slightly more effective against Bel-7402 cell line than cisplatin. Using ethidium bromide as a fluorescence probe, the binding mode of the La(III)-L complex to calf-thymus DNA was studied spectroscopically. For comparison, the same measurements were carried out with La(III)-Phen [La(III)-1,10-phenanthroline complex] and La(III)-Val [La(III)-L-valine complex]. The results indicate that the La(III)-L and La(III)-Phen complexes possibly interact with calf-thymus DNA by both intercalative and coordination binding, whereas the La(III)-Val complex interacts with calf-thymus DNA by coordination binding. Kinetics of binding of the three complexes to DNA is for the first time studied using ethidium bromide as a fluorescence probe with stopped-flow spectrophotometer under pseudo-first-order condition. The strong two-step mechanisms in the process of the La(III)-L and La(III)-Phen complexes and one step in the process of the complex La(III)-Val interacting with DNA are observed, and the k(obs) (observed pseudo-first-order rate constant) and E(a) (observed energy of activation) values of binding to DNA are obtained.     

Synthesis, characterization and DNA-binding properties of La(III) complex of chrysin

A novel La(III) complex of chrysin (5,7-dihydroxyflavone) was synthesized and characterized by UV, IR, 1H NMR, thermogravimetry/differential thermal analysis (TG/DTA) and elementary analyses. The interactions of the La(III) complex and chrysin with calf thymus DNA were investigated by spectrophotometric methods and viscosity measurements. The intrinsic binding constants of La(III) complex and chrysin are 1.29 x 10(6) and 5.44 x 10(5) M(-1), respectively. Experimental results indicated that La(III) complex and chrysin can both bind to DNA by intercalation modes, but the binding affinity of La(III) complex is much higher than that of chrysin. Comparative antitumor activities of La(III) complex and chrysin were tested by MTT and SRB methods. The results show that at the concentration of 10 microM for chrysin and La(III) complex, the inhibitory ratios of La(III) complex against the tested tumor cells were higher than those of chrysin.     

Synthesis, characterization, and DNA-binding properties of Ln(III) complexes containing gatifloxacin

Four novel water-soluble complexes of Ln(III) with gatifloxacin (HGA), [La(HGA)3Cl3] x 2H2O, [Nd(HGA)3Cl3] x 2H2O, [Eu(HGA)3Cl3] x 2H2O, [Tb(HGA)3Cl3] x 2H2O, have been synthesized and characterized by elemental analyses, molar conductivities, IR spectra, fluorescence spectra, and thermogravimetry/differential thermal analysis (TG-DTA). In addition, the DNA-binding properties of the ligand and its complexes have been investigated by absorption, fluorescence spectra, and viscosity measurements. The experimental results indicated that the complexes and ligand bind to DNA via groove binding mode.     

Complexes of lanthanoid salts with macrocyclic ligands. Part 32. Synthesis and characterization of the complexes between lanthanoid nitrates and a tetraoxadiaza macrocycle

Lanthanoid nitrates react with 1,7,10,16-tetraoxa- 4,13-diaza-N,N′-dimethylcyclooctadecane, Me₂(2,2), to give complexes with two different metal:ligand ratios, 1:1 (Ln = La, Ce, Tb) and 4:3 (Ln = Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho). The complexes were isolated from anhydrous solutions in acetonitrile and characterized by elemental analysis, X-ray diffraction, magnetic susceptibility measurements and vibrational analysis.The La and Ce 1:1 complexes are non-ionic and probably 12-coordinated, with the metal ion bound to the six donor atoms of the ligand and to three bidentate nitrate ions. The 4:3 complexes are ionic; they contain three bis(nitrato) complex cations [Ln(NO₃)₂·Me₂(2,2)]⁺ and one hexakis(nitrato) anion [Ln(NO₃)₆]³⁻. Spectroscopic data, including luminescence spectra, point to the 1:1 Tb-complex as being a 4:3 complex with an additional outer-sphere coordinated molecule of ligand.In solution, the 1:1 complexes remain essentially non-ionic, although some dissociation cannot be ruled out, whereas the 4:3 complexes behave as 2:1 (of even 3:1) electrolytes.     

Development of novel copper(II) complexes of benzothiazole-N-sulfonamides as protective agents against superoxide anion. Crystal structures of [Cu(N–2-(4-methylbenzothiazole)benzenesulfonamidate)2(py)2] and [Cu(N–2-(6-nitrobenzothiazole)naphthalenesulfonamidate)2(py)2]

Copper(II) ternary complexes based on the novel benzothiazole- N-sulfonamides, HL1 ( N-2-(4-methylbenzothiazole)benzenesulfonamide) and HL2 ( N-2-(6-nitrobenzothiazole)naphthalenesulfonamide) ligands, and pyridine have been synthesized and characterized. Complexes [Cu(L1)(2)(py)(2)] (1). and [Cu(L2)(2)(py)(2)] (2). were chemically characterized and their structures determined by means of single crystal X-ray analysis. In both compounds the Cu(II) ion is coordinated to four N atoms in a nearly square planar arrangement. The Cu-N bond distances are similar to those of Cu(2)Zn(2)SOD. The SOD mimetic activity of the complexes was determined both in vitro and in vivo. For determining the SOD-like activity of the complexes in vivo, we have developed a new method based on the complexes' protective effect on a delta sod1mutant of Saccharomyces cerevisiae against free radicals generated by hydrogen peroxide and menadione as well as free radicals produced in the cellular respiration process. The results have shown that complex 1 presents a protective action against oxidative stress induced by menadione or H(2)O(2) and that both complexes 1 and 2 protect against free radicals generated in cellular respiration.     

Synthesis, crystal structure, cytotoxic activity and DNA-binding properties of the copper (II) and zinc (II) complexes with 1-[3-(2-pyridyl)pyrazol-1-ylmethyl]naphthalene

A new ligand L, 1-[3-(2-pyridyl)pyrazol-1-ylmethyl]naphthalene, and its two metal complexes, [Cu(L)3](ClO4)2 (1) and [Zn(L)3](ClO4)2(H2O)2 (2), have been synthesized and characterized. The crystal structure of complex 1 was determined by single crystal X-ray diffraction, which crystallized in monoclinic, space group P2(1)/n with unit cell parameters, a = 12.710(4) angstroms, b = 12.135(3) angstroms, c = 33.450(9) angstroms, beta = 93.281(5) degrees and Z = 4. The Cu atom was six-coordinated to N(1), N(2), N(4), N(5), N(7) and N(8) from three L ligands and formed a slightly distorted octahedral geometry. Complexes 1 and 2, and ligand L were subjected to biological tests in vitro using three different cancer cell lines (HL-60, BGC-823 and MDA-MB-435). Complex 1 showed significant cytotoxic activity against three cancer cell lines. The interactions of complexes 1 and 2, and ligand L with calf thymus DNA were then investigated by thermal denaturation, viscosity measurements and spectrophotometric methods. The experimental results indicated that complexes 1 and 2 bound to DNA by intercalative mode via the ligand L. The intrinsic binding constants of complexes 1 and 2, and ligand L with DNA were 1.8 x 10(4), 5.4 x 10(3) and 2.76 x 10(3) M(-1), respectively.     

The kinetics and mechanisms of the reaction of iron(III) with gallic acid, gallic acid methyl ester and catechin.

The kinetics and mechanisms of the reactions of a number of pyrogallol-based ligands with iron(III) have been investigated in aqueous solution at 25 degrees C and ionic strength 0.5 M NaClO(4). Mechanisms have been proposed which account satisfactorily for the kinetic data. These are generally consistent with a mechanism in which the 1:1 complex that is formed initially when the metal reacts with the ligand subsequently decays through an electron transfer reaction. There was also some evidence for the formation of a 1:2 ligand-to-metal complex at higher pH values. The kinetics of complex formation were investigated with either the ligand or metal in pseudo-first-order excess. Rate constants for k(1) of 2.83(+/-0.09)x10(3), 1.75(+/-0.045)x10(3) and 3300(+/-200) M(-1) s(-1) and k(-1) of 20(+/-6.0), 35(+/-13) and 25+/-7.6 M(-1) s(-1) have been evaluated for the reaction of Fe(OH)(2+) with gallic acid, gallic acid methyl ester and catechin, respectively. The stability constant of each [Fe(L)](+) complex has been calculated from the kinetic data. The iron(III) assisted decomposition of the initial iron(III) complex formed was investigated. Analysis of the kinetic data yielded both the equilibrium constants for protonation of the iron(III) complexes initially formed together with the rate constants for the intramolecular electron transfers for gallic acid and gallic acid methyl ester. All of the suggested mechanisms and calculated rate constants are supported by calculations carried out using global analysis of time-dependent spectra.     

Dynamics of beta2-adrenergic receptor-ligand complexes on living cells

The agonist-induced dynamic regulation of the beta(2)-adrenergic receptor (beta(2)-AR) on living cells was examined by means of fluorescence correlation spectroscopy (FCS) using a fluorescence-labeled arterenol derivative (Alexa-NA) in hippocampal neurons and in alveolar epithelial type II cell line A549. Alexa-NA specifically bound to the beta(2)-AR of neurons with a K(D) value of 1.29 +/- 0.31 nM and of A549 cells with a K(D) of 5.98 +/- 1.62 nM. The receptor density equaled 4.5 +/- 0.9 microm(-2) in neurons (rho(N)) and 19.9 +/- 2.0 microm(-2) in A549 cells (rho(A549)). Kinetic experiments revealed comparable on-rate constants in both cell types (k(on) = 0.49 +/- 0.03 s(-1) nM(-1) in neurons and k(on) = 0.12 +/- 0.02 s(-1) nM(-1) in A549 cells). In addition to the free ligand diffusing with a D(free) of (2.11 +/- 0.04) x 10(-6) cm(2)/s, in both cell types receptor-ligand complexes with two distinct diffusion coefficients, D(bound1) (fast lateral mobility) and D(bound2) (hindered mobility), were observed [D(bound1) = (5.23 +/- 0.64) x 10(-8) cm(2)/s and D(bound2) = (6.05 +/- 0.23) x 10(-10) cm(2)/s for neurons, and D(bound1) = (2.88 +/- 1.72) x 10(-8) cm(2)/s and D(bound2) = (1.01 +/- 0.46) x 10(-9) cm(2)/s for A549 cells]. Fast lateral mobility of the receptor-ligand complex was detected immediately after addition of the ligand, whereas hindered mobility (D(bound2)) was observed after a delay of 5 min in neurons (up to 38% of total binding) and of 15-20 min in A549 cells (up to 40% of total binding). Thus, the receptor-ligand complexes with low mobility were formed during receptor regulation. Consistently, stimulation of receptor internalization using the adenylate cyclase activator forskolin shifted the ratio of receptor-ligand complexes toward D(bound2). Intracellular FCS measurements and immunocytochemical studies confirmed the appearance of endocytosed receptor-ligand complexes in the cytoplasm subjacent to the plasma membrane after stimulation with the agonist terbutaline (1 microM). This regulatory receptor internalization was blocked after preincubation with propranolol and with a cholesterol-complexing saponin alpha-hederin.     

In vitro toxicity of palladium(II) and gold(III) porphyrins and their aqueous metal ion counterparts on Trypanosoma brucei brucei growth

The trypanocidal effects of aqueous gold(III) and palladium(II) and their metalloporphyrin derivatives on Trypanosoma brucei brucei growth in culture have been studied using an Alamar Blue indicator assay. All the experiments were conducted in the dark. As previously described for mercury(II), cadmium(II) and lead(II) porphyrins [Chem.-Biol. Interact. 139 (2002) 177], the toxicity of the metalloporphyrin complex of palladium(II) to T. b. brucei parasites was much higher compared to the aqueous free palladium(II) and free base porphyrin. Palladium(II) porphyrin, free palladium(II), and the free base porphyrin were trypanocidal to T. b. brucei at concentrations >1.5 x 10(-6), >6.1 x 10(-6) and >1.9 x 10(-5) M, respectively. While gold(III) porphyrin was effective against the parasites at concentrations >4.8 x 10(-6) M, its aqueous gold(III) was toxic at concentrations as low as 2.0 x 10(-7) M due to the generation of free radicals in the presence of this metal ion which enhanced its toxicity to the T. b. brucei parasites. Although some cell division was observed in some of the cells treated with palladium(II) porphyrin, some dividing cells had no nucleus due to unequal division and delivery of the nuclei into the daughter cells. As a result, the rate of cell division decreased with time and cell death occurred within 24 h. Interestingly, trypanosomes treated with metalloporphyrin complexes displayed different morphological features from those cells treated with free base porphyrin or metal ions. Of all the porphyrins and free metal ions tested, only mercury(II) porphyrin and aqueous gold(III) ion were toxic to the trypanosomes in the 10(-7) M range. The chemotherapeutic potential of these observations is discussed.     

Kinetic and mechanistic studies of the NO*-mediated oxidation of oxymyoglobin and oxyhemoglobin

The second-order rate constants for the reactions between nitrogen monoxide and oxymyoglobin or oxyhemoglobin, determined by stopped-flow spectroscopy, increase with increasing pH. At pH 7.0 the rates are (43.6 +/- 0.5) x 10(6) M(-1) x s(-1) for oxymyoglobin and (89 +/- 3) x 10(6) M(-1) x s(-1) for oxyhemoglobin (per heme), whereas at pH 9.5 they are (97 +/- 3) x 10(6) M(-1) x s(-1) and (144 +/- 3) x 10(6) M(-1) x s(-1), respectively. The rate constants for the reaction between oxyhemoglobin and NO* depend neither on the association grade of the protein (dimer/tetramer) nor on the concentration of the phosphate buffer (100-1 mM). The nitrogen monoxide-mediated oxidations of oxymyoglobin and oxyhemoglobin proceed via intermediate peroxynitrito complexes which were characterized by rapid scan UV/vis spectroscopy. The two complexes MbFe(III)OONO and HbFe(III)OONO display very similar spectra with absorption maxima around 500 and 635 nm. These species can be observed at alkaline pH but rapidly decay to the met-form of the proteins under neutral or acidic conditions. The rate of decay of MbFe(III)OONO increases with decreasing pH and is significantly larger than those of the analogous complexes of the two subunits of hemoglobin. No free peroxynitrite is formed during these reactions, and nitrate is formed quantitatively, at both pH 7.0 and 9.0. This result indicates that, as confirmed from protein analysis after reacting the proteins with NO* for 10 times, when peroxynitrite is coordinated to the heme of myoglobin or hemoglobin it rapidly isomerizes to nitrate without nitrating the globins in physiologically significant amounts.