Spectroscopic characterization of 2-isopropylmalic acid-aluminum(III) complex

Spectroscopic elucidation of a 2-isopropylmalic acid (2-iPMA)-aluminum(III) complex has been carried out using (1)H, (13)C and (27)Al NMR spectroscopy, diffusion-ordered NMR spectroscopy (DOSY) and electrospray ionization mass spectrometry (ESI-MS). 2-iPMA is secreted by Saccharomyces cerevisiae and can dissolve Al(III) in the culture medium. The (1)H chemical shift perturbation and (1)H DOSY clearly indicated the formation of the 2-iPMA-Al(III) complex. The measurements of (13)C and (27)Al NMR spectroscopy and ESI-MS demonstrated that the major form of a complex is comprised four 2-iPMA and two Al(III) species. This compound is expected to possess strong Al(III)-detoxification capability.     

Synthesis and structural determination of a new five-coordinate iron(III) porphyrin containing monoanion 1,4-phenyldicyanamide as axial ligand

A new five coordinate and stable iron(III) heme analog, [Fe^III(OEP)(DicydH)], where OEP is the dianion of octaethylporphyrin and DicydH = monoanion of 1,4-phenyldicyanamide, has been synthesized. The compound has been characterized by different spectroscopic methods ¹H NMR, UV-Vis, IR as well as elemental analysis. ¹H NMR spectroscopy and magnetic moment measurements show that [Fe^III(OEP)(DicydH)] is paramagnetic and iron is five-coordinate. The structure of [Fe^III(OEP)(DicydH)] has been determined by X-ray diffraction analysis, that it is similar with a P2₁/c space group in the monoclinic crystal system. The crystal structure of the complex is stabilized by hydrogen bonds of the type N-H?N. Electrochemical of [Fe^III(OEP)(DicydH)] has been studied by cyclic voltammetry.     

Interactions of aluminium(III) with glycerolphosphates and glycerophosphorylcholine

The complexation of aluminium(III) with glycerol-1-phosphate (G1P) and glycerol-2-phosphate (G2P) in aqueous solutions has been studied as a function of pH, by pH-potentiometry, 31P NMR spectroscopy and ESI mass spectrometry. Various mononuclear complexes (MLH(2)(3+), MLH(2+), ML(+), ML(2)H, ML(2)(-)) and polynuclear species (M(3)L(3)H(-1)(2+), M(3)L(2)H(-n)((n-5)-) with n=5, 6, 7, M(2)L(2)H(-1)(+) ) are formed in the system where the full protonated ligands are noted LH(2). NMR experiments clearly show that G1P and G2P already interact with Al(III) at pH 1. The potentiometric results are confirmed by ESI measurements and 31P NMR studies. No metal ion-induced deprotonation and coordination of the alcoholic-OH functions seem to occur during the complexation. The situation is very different for the glycerophosphorylcholine ligand (GPC identical with LH). Only the complex ML(3+) is formed in aqueous solution with a relatively low formation constant (K=5 at 37 degrees C). This species is clearly identified in 31P and 27Al NMR spectra. The complexation study as a function of the temperature allowed us to determine the thermodynamic parameters of the complex formation. The complexation is not governed by the reaction enthalpy that is found to be positive but by the entropy that is largely positive.     

Synthesis, molecular structure, and properties of six-coordinate iron(III) porphyrin, [OEPFe(Pz)2]ClO4

The effect of pyrazine as axial ligand on the formation and coordination of heme analogue has been studied. A new six coordinate and stable iron(III) heme analogue, [OEPFe^III(Pz)₂]ClO₄, where OEP is octaethylporphyrin and Pz is pyrazine, has been isolated. The compound has been characterized by different spectroscopic methods ¹H NMR, UV-Vis, IR as well as elemental analysis. ¹H NMR spectroscopy and magnetic moment measurements show that [OEPFe^III(Pz)₂]ClO₄ is paramagnetic and iron is six coordinate. The structure of [OEPFe^III(Pz)₂]ClO₄ has been determined by X-ray diffraction analysis. The four Fe-N_p, bond distances have average values of 1.985 Å.     

Fe(III).ATP complexes. Models for ferritin and other polynuclear iron complexes with phosphate

Polynuclear iron complexes of Fe(III) and phosphate occur in seawater and soils and in cells where the iron core of ferritin, the iron storage protein, contains up to 4500 Fe atoms in a complex with an average composition of (FeO.OH)8FeO.OPO3H2. Although phosphate influences the size of the ferritin core and thus the availability of stored iron, little is known about the nature of the Fe(III)-phosphate interaction. In the present study, Fe-phosphate interactions were analyzed in stable complexes of Fe(III).ATP which, in the polynuclear iron form, had phosphate at interior sites. Such Fe(III).ATP complexes are important not only as models but also because they may play a role in intracellular iron transport and in iron toxicity; the complexes were studied by extended x-ray absorption fine structure, EPR, NMR spectroscopy, and measurement of proton release. Mononuclear iron complexes exhibiting a g' = 4.3 EPR signal were formed at Fe:ATP ratios less than or equal to 1:3, and polynuclear iron complexes (Fe greater than or equal to 250, EPR silent at g' = 4.3) were formed at an Fe:ATP ratio of 4:1. No NMR signals due to ATP were observed when Fe was in excess (Fe:ATP = 4:1). Extended x-ray absorption fine structure analysis of the polynuclear Fe(III).ATP complex was able to distinguish an Fe-P distance at 3.27 A in addition to the octahedral O at 1.95 A and 4-5 Fe atoms at 3.36 A. The Fe-O and Fe-Fe distances are the same as in ferritin, and the Fe-P distance is analogous to that in another metal-ATP complex. An observable Fe-P environment in such a large polynuclear iron cluster as the Fe(III).ATP (4:1) complex indicates that the phosphate is distributed throughout rather than merely on the surface, in contrast to earlier models of chelate-stabilized iron clusters. Complexes of Fe(III) and ATP similar to those described here may form in vivo either as normal components of intracellular iron metabolism or during iron excess where the consequent alteration of free nucleotide triphosphate pools could contribute to the observed toxicity of iron.     

Metallocene basicity. VIII. Protonation of bridge substituted ferrocenophanes in strong acid media

A series of bridge substituted [3]-, [4]-, and [5]- ferrocenophanes have been prepared and characterized by ¹H NMR and mass spectroscopy. In trifluoroboric acid, HBF₃OH, solution these ferrocenophanes protonate at the iron to form long-lived species which can be studied by ¹H NMR. Analysis of the complex ¹H NMR spectra of the protonated species suggests that bridge substituents either slow or block the free oscillation of the rings and bridges. The iron-hydrogen chemical shift values have been shown to depend only on the length of the bridge and seem to be insensitive to substituents on the bridge.     

Complexes of aluminium(III) with glucose-6-phosphate in aqueous solutions

The interaction of aluminium(III) with glucose-6-phosphate (GP: LH2) in aqueous solutions has been studied from pH 1 to pH 8, by pH-potentiometry and multinuclear (31P, 27Al, 13C) NMR spectroscopy. Various mononuclear species (MLH2, MLH, ML, ML2H, ML2 and MLH(-3)) and dinuclear complexes M2L2H-n (n=1-4) are formed in the system. NMR clearly indicates that GP is already bound to Al(III) at pH 1. The potentiometric speciation results are confirmed and completed by spectroscopic experiments. Many peaks are observed in the 31P NMR spectra suggesting the formation of isomeric species. An attempt to assign the signals to the corresponding complexes is made, allowing a discussion about their structure. Interestingly enough no metal ion-induced deprotonation and coordination of the alcoholic-OH functions have been observed.     

Modification of the heme·heme oxygenase system with iron and cobalt tetrasulfonated phthalocyanines

Modification of heme·heme oxygenase by iron(III) and cobalt(II) tetrasulfonated phthalocyanines has been performed. New compounds have been isolated and their properties have been investigated by difference spectroscopy, electrophoresis, molecular weight estimation, electron paramagnetic resonance (EPR) and carboxymethylation at histidyl groups. Spectrophotometric titration data indicate the ratio of the reagents in this process to be 1:1. The visible absorption spectra show the main peak at 650 nm for the iron compound and 682 nm for the cobalt one. Electrophoresis and molecular weight estimation show both complexes to be monomers. Cobalt(II) tetrasulfonated phthalocyanine, under aerobic conditions with heme oxygenase protein, undergoes autooxidation to the cobalt(III) complex, as has been proved by EPR and spectroscopic data. Iron and cobalt phthalocyanine modified heme·heme oxygenase with excess dithionite is reduced at the phthalocyanine ligand. In the presence of oxygen, the reduction product transforms into oxygenated Fe(III)Lheme oxygenase or Co(III)heme oxygenase, respectively. Reduction of the iron(III) model complex with ascorbic acid under anaerobic conditions leads to degradation of the phthalocyanine moiety, while Co(III)heme oxygenase with ascorbic acid is reduced to Co(II)Lheme oxygenase. As has been shown by carboxymethylation of the heme oxygenase protein at the histidine residues, the predominant binding site of both phthalocyanine complexes is the heme-binding histidyl residue. There is evidence that there is a second binding site with lower affinity towards Co(II)L on the heme oxygenase protein. Iron and cobalt tetrasulfonated phthalocyanines are not able to displace heme from the heme·heme oxygenase complex. In this reaction the iron complex undergoes degradation and the cobalt one gives a hybrid compound with heme·heme oxygenaseHeme oxygenase protein complexes with iron and cobalt tetrasulfonated phthalocyanines do not exhibit activity in their oxidative degradation.     

The solution conformation of the Le chi group

The solution conformation of the non-reducing terminal Gal beta 1----4 (Fuc alpha 1----3)GlcNAc (Lewis X or Le chi) group in the oligosaccharide Lacto-N-fucopentaose (LNFP) III has been determined by high resolution 1H NMR spectroscopy and semi-empirical quantum mechanical calculations. The two methods give the same single conformer for the Le chi group showing close packing of the Gal and Fuc rings. The metal binding properties and homotypic oligomer formation of LNFP III have also been investigated by NMR spectroscopy. No evidence for metal binding or high-affinity homotypic oligomer formation has been found.     

Iron corrolates: unambiguous chloroiron(III) (corrolate)(2-.) pi-cation radicals

The structures, electron configurations, magnetic susceptibilities, spectroscopic properties, molecular orbital energies and spin density distributions, redox properties and reactivities of iron corrolates having chloride, phenyl, pyridine, NO and other ligands are reviewed. It is shown that with one very strong donor ligand such as phenyl anion the electron configuration of the metal is d(4)S=1 Fe(IV) coordinated to a (corrolate)(3-) anion, while with one weaker donor ligand such as chloride or other halide, the electron configuration is d(5)S=3/2 Fe(III) coordinated to a (corrolate)(2-.) pi-cation radical, with antiferromagnetic coupling between the metal and corrolate radical electron. Many of these complexes have been studied by electrochemical techniques and have rich redox reactivity, in most cases involving two 1-electron oxidations and two 1-electron reductions, and it is not possible to tell, from the shapes of cyclic voltammetric waves, whether the electron is added or removed from the metal or the macrocycle; often infrared, UV-Vis, or EPR spectroscopy can provide this information. (1)H and (13)C NMR spectroscopic methods are most useful in delineating the spin state and pattern of spin density distribution of the complexes listed above, as would also be expected to be the case for the recently-reported formal Fe(V)O corrolate, if this complex were stable enough for characterization by NMR spectroscopy. Iron, manganese and chromium corrolates can be oxidized by iodosylbenzene and other common oxidants used previously with metalloporphyrinates to effect efficient oxidation of substrates. Whether the "resting state" form of these complexes, most generally in the case of iron [FeCl(Corr)], actually has the electron configuration Fe(IV)(Corr)(3-) or Fe(III)(Corr)(2-.) is not relevant to the high-valent reactivity of the complex.     

Nuclear magnetic resonance determination of metal-proton distances in a synthetic calcium binding site of rabbit skeletal troponin C

The binding of gadolinium to a synthetic peptide of 13 amino acid residues representing the calcium binding loop of site 3 of rabbit skeletal troponin C [AcSTnC(103-115)amide] has been studied by using proton nuclear magnetic resonance (1H NMR) spectroscopy. In particular, the proton line broadening and enhanced spin-lattice relaxation have been used to determine proton-metal ion distances for several assigned nuclei in the peptide-metal ion complex. These distances have been used in conjunction with other constraints and a distance algorithm procedure to demonstrate that the structure of the peptide-metal complex as shown by 1H NMR is consistent with the structure of the EF calcium binding loop in the X-ray structure of parvalbumin but that the available 1H NMR distances do not uniquely define the solution structure.     

Effect of substituents on complex stability aimed at designing new iron(III) and aluminum(III) chelators

The solution equilibria of iron(III) and aluminum(III) with two classes of hard ligands (catechol, salicylic acid and their nitro-derivatives) have been reliably studied by potentiometric, spectrophotometric and NMR spectroscopy. The effect of the nitro substituent on the binding properties of catechol and salicylic acid has been examined thoroughly. The inductive and resonance properties of the substituent that, as expected, lower the basicity of the phenolic and carboxylic groups, lead to a general decrease in both protonation and complex formation constants. This decrease causes an increase in pM of between 0.2 and 1.1 pM units for the nitro-substituted salicylates and of about 4 units for 4-nitrocatechol, with a significantly higher chelating efficacy. The influence of the substituent on catechol and salicylic acid is discussed in detail on the basis of conditional constants at pH 7.4.     

Inclusion complexes of pyrimethamine in 2-hydroxypropyl-beta-cyclodextrin: characterization, phase solubility and molecular modelling

The inclusion complexation of pyrimethamine in 2-hydroxypropyl-beta-cyclodextrin has been investigated by 2D (1)H NMR, FTIR and UV/visible spectroscopy and also by molecular modelling methods (AM1, PM3, MM3). From the phase-solubility diagram a linear increase was observed in pyrimethamine aqueous solubility in the presence of 2-hydroxypropyl-beta-cyclodextrin, evidencing the formation of a soluble inclusion complex. According to the continuous variation method (Job's plot) applied to fluorescence measurements, a 1:1 stoichiometry has been proposed for the complex. Concerning the structure of the complex, a Cl-in orientation of pyrimethamine in the 2-hydroxypropyl-beta-cyclodextrin cavity has been proposed from the theoretical calculations, being confirmed by two-dimensional (1)H NMR spectroscopy (ROESY). The thermal behaviour has also been studied, providing complementary evidences of complex formation.     

Binding of the Mn(III) complex of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin to DNA. Effect of ionic strength

Interactions of the water-soluble Mn(III) complex of meso-tetrakis (4-N-methyl-pyridiniumyl) porphyrin (Mn(III)TMPyP) with DNA in aqueous solutions at low (0.01 M) and high (0.2 M) ionic strengths have been studied by optical absorption, resonance light scattering (RLS) and 1H NMR spectroscopies. Optical absorption and RLS measurements have demonstrated that in DNA solutions at low ionic strength the Mn(III)TMPyP form aggregates, which are decomposed at DNA excess. At high ionic strength the aggregation was not observed. We explain this effect by assuming that upon increase in ionic strength, Mn(III) TMPyP dislocates from the DNA sites, which produces better conditions for the porphyrin aggregation, to sites where the aggregation is hindered. The 1H NMR data demonstrated that the aggregation observed at low ionic strength reduces the paramagnetism of Mn(III)TMPyP. This phenomenon was not observed at the high ionic strength in the absence of aggregation.     

Synthesis, characterization, and DNA binding studies of some mixed-ligand platinum(II) complexes of 1,10-phenanthroline and amino acids

A series of complexes of the type [Pt(phen)(AA)]+ (where AA is the anion of glycine, L-alanine, L-leucine, L-phenylalanine, L-tyrosine, or L-tryptophan) has been synthesized. These complexes have been characterized by electronic absorption, infrared, and 1H NMR spectroscopy. The interaction of these complexes with calf thymus DNA has been studied using fluorescence spectroscopy. They inhibit the intercalation of ethidium bromide in DNA by intercalative binding at low concentrations and show nonintercalative binding at higher concentrations.     

Preparation, UV-Vis, IR and H NMR spectra, and molecular structure of the complex ion (η-carbonato)(α,α,α,α-tetrakis (o-pivalamidophenyl)porphinato)ferrate(III)

An iron(III) porphyrin complex containing a bidentate carbonato axial ligand has been synthesized for the first time and fully characterized by UV-Vis, IR and ¹H NMR spectroscopies and X-ray crystallography. Proton NMR data for the isolated species is in accordance with high-spin (S = 5/2) ferric derivative. The crystal structure of the (cryptand-222)potassium(+) (dihaptocarbonato)(α,α,α,α-terakis(o-pivalamidophenyl)(porphinato)ferrate(III) chlorobenzene has been determined. This structure confirms the high-spin-state of the carbonato derivative and shows that the coordination sphere of the iron atom is strongly affected by the asymmetric bidentate (η²) mode of the carbonato axial ligand.     

Reaction of iron(III) with theaflavin: complexation and oxidative products

Theaflavins are a family of compounds, whose chemistry has been sparsely investigated. They can comprise up to 40% the dry weight of black tea. They are known to chelate metals, however very little knowledge exists on the mechanisms involved. There is some correlation between both of these areas in that following degradation of the iron theaflavin complex, subsequent redox reactions may lead to the formation of similar products on both occasions. The interaction of iron(III) with theaflavin at pH < 3.0 is investigated by means of liquid chromatography mass spectroscopy (LC-MS), stopped flow spectroscopy and multivariate data analysis. Iron theaflavin complexes are formed which subsequently decay to form a number of oxidative species. The difficulties involved in the elucidation of the structure of polymeric phenolic compounds from black tea has been highlighted by numerous authors. The intermediates and major low molecular weight oxidised theaflavin products from the reaction of excess iron with theaflavin have been detected and identified using multivariate data analysis of diode array spectroscopic data. It is not possible to characterise the extremely polar high molecular weight oxidation products obtained from polyphenol oxidation. High performance liquid chromatography (HPLC) and electrospray mass spectroscopy (ES-MS) detected the low molecular weight oxidised theaflavin species present in the system. Enzymatic oxidation of theaflavin using peroxidase (POD) resulted in the formation of one major low molecular weight species oxidative product, which was fully characterised using nuclear magnetic resonance spectroscopy (NMR), high performance liquid chromatography (HPLC), electrospray mass spectroscopy (ES-MS), UV-visible (UV-Vis) and Fourier transform infra-red spectroscopy (FT-IR). The major objective of this work is to investigate the reaction of iron(III) with theaflavin and to add some insight into the mechanistic interaction of iron(III) with this family of compounds.     

Spectroscopic study of a water-soluble iron(III) meso-tetrakis(4-N-methylpyridiniumyl) porphyrin in aqueous solution: effects of pH and salt

The equilibrium behavior of cationic iron(III) meso-tetrakis(4-N-methyl-pyridiniumyl) porphyrin, Fe(III)TMPyP, in aqueous solution was studied as a function of pH by optical absorption, EPR and (1)H NMR spectroscopies. The presence of several Fe(III)TMPyP species in solution was unequivocally demonstrated: monomeric porphyrin species (a monoaqueous five-coordinated complex, a diaaqueous six-coordinated complex and a monoaqueous-hydroxo six-coordinated complex), a micro-oxo dimer and a bis-hydroxo complex. The addition of salt to the porphyrin solution leads to a simplification of the equilibrium as a function of pH. In this case, only three species were observed in solution: a monomeric porphyrin species, a micro-oxo dimer and a bis-hydroxo complex. Optical absorption, EPR and (1)H NMR spectra contributed to the characterization of these species. Four critical pH values (pK) for Fe(III)TMPyP were obtained in pure buffer and only three pK values were observed in the presence of NaCl. The addition of salt favors the presence of the dimeric species in solution and simplifies the equilibrium in the acidic pH range.     

A spectroscopic and electrochemical study of the interaction between copper (II) glycylglycyl-L-histidine-N-methylamide and iron (III) tetra-p-sulfophenylporphine

A binuclear complex has been produced by the reaction of an iron porphyrin (sodium tetra-p-sulfophenylporphine iron (III)-FeTPPS) with a copper metallo-tripeptide (copper (II) glycylglycyl-L-histidine-N-methylamide-CuGGH) in aqueous solution. The system has been characterized by electron spin resonance (ESR) spectroscopy, optical absorption spectroscopy, and electrochemical methods. Room-temperature ESR spectra of the copper complex and low-temperature ESR spectra of the iron porphine provide evidence for the formation of a binuclear complex. These findings are supported by absorption spectroscopy and electrochemical studies, and lead to a value of ca. 2 X 10(-3) M-1 (at room temperature) for the equilibrium constant for complex formation. The relevance of this system to the enzymic active site of mammalian cytochrome c oxidase is discussed.     

1H and 119Sn magnetic resonance study of the SnIV protoporphyrin IX complex of equine myoglobin. Structure of the porphyrin-binding pocket

Tin protoporphyrin IX (SnPP) is being used in the treatment of hyperbilirubinemia. We have studied the SnPP complex with equine myoglobin (EqMb) by 1H and 119Sn nuclear magnetic resonance spectroscopy (NMR) as a general model for SnPP interaction with hemoproteins. The complex formed from SnPP and EqMb, SnPP.EqMb, was found to have essentially the same porphyrin-binding pocket as EqMbCO, including the same porphyrin orientation in the major form of EqMbCO. 119Sn NMR spectroscopy has been used to demonstrate that the proximal His93F8-metal coordination is likely to be intact in SnPP.EqMb. Minor shifts in the side chain positions of some of the residues are indicated, possibly reflecting the presence of water in the sixth coordination site. SnPP.EqMb appears to be stable; it persists at room temperature for weeks and exhibits very slow exchange rates (2H for 1H) for a large number of amide protons in the pH range 7-9.