Deprotonated Hydroxyl Group Research Articles

Ruthenium(II) 2-hydroxybenzophenone N(4)-substituted thiosemicarbazone complexes

New ruthenium(II) complexes with 2-hydroxybenzophenone N(4)-substituted (Me, Ph and/or piperidyl) thiosemicarbazones have been prepared and characterised by elemental analysis, molar conductivity, thermal analysis, spectroscopy (i.r., 1H-n.m.r. and u.v.–vis.) and by cyclic voltammetry. The thiosemicarbazones coordinate to ruthenium(II) as mononegative tridentate ligands via the deprotonated hydroxyl group, N1 nitrogen and thione sulphur centres. The redox properties, nature of the electrode processes and the stability of the complexes towards oxidation in CH2Cl2 are discussed. The change in the E 1/2 values of the complexes can be related to the basicity of the N(4)-substituents. All the complexes display an irreversible one-electron charge-transfer couple in the potential range studied.

Synthesis, characterization, and biological relevance of hydroxypyrone and hydroxypyridinone complexes of molybdenum

We have prepared a number of complexes of the type cis-MoO2L2 where L represents a hydroxypyronato or hydroxypyridinonato ligand. Both the maltol (3-hydroxy-2-methyl-4-pyrone, Hma) and kojic acid (5-hydroxy-2-hydroxymethyl-4-pyrone, Hka) complexes, cis-MoO2(ma)2 (1) and cis-MoO2(ka)2 (2), have been characterized by X-ray diffraction studies. The pyrone ligands are bound to molybdenum in a cis bidentate fashion via the deprotonated hydroxyl groups and the ketone moieties. Crystals of 1 are orthorhombic, a = 12.107 (1), b = 8.6169 (8), c = 16.472 (1) Å, Z = 4, space group Pca21, and those of 2 are monoclinic, a = 8.4591 (5), b = 16.3453 (10), c = 10.2954 (7) Å, β = 103.0320 (10)°, Z = 4, space group P21/c. Hydroxypyridinone molybdenum complexes have been prepared for both maltol and kojic acid derivatives with the substituents Me, n-Pr, CH2Ph, Ph at the ring nitrogen. Crystals of the 3-hydroxy-2-methyl-1-phenyl-4-pyridinone (Hppp) derivative, MoO2(ppp)2 (9), are monoclinic, a = 10.9476 (6), b = 13.5353 (9), c = 17.4877 (10) Å, β = 93.465 (4)°, Z = 4, space group P21/n. Initial investigations into the effects molybdenum compounds have on diabetic hearts are presented. Both Na2MoO4 (used as a control) and 1 were effective in lowering blood glucose and free fatty acid levels. Diabetic rats treated with molybdate showed significant improvements in postischemic cardiac function.Key words: molybdenum, hydroxypyrones, hydroxypyridinones, heart function.

The first binuclear Mo–S cluster compound containing citrate ligands, K 5(NH 4)[Mo 2O 2(μ-S) 2(C 6H 4O 7) 2]·CH 3OH·5H 2O, characterized by X-ray single crystal structure determination

The new Mo–S cluster anion, [Mo 2O 2(μ-S) 2(C 6H 4O 7) 2] 6−, containing an [Mo 2O 2(μ-S 2)] 2+ core with tridentate terminal citrate ligands, has been prepared by reaction of ammonium tetrathiomolybdate and ammonium citrate and isolated as the mixed ammonium/potassium salt, K 5(NH 4) [Mo 2O 2(μ-S) 2(C 6H 4O 7) 2]·CH 3OH·5H 2O ( 1). The crystal structure of 1 (monoclinic, space group P21/ n (No. 14) a = 11.004(1), b = 12.731(7), c = 23.454(4) Å, β = 94.01(1)°, V = 3277(2) Å 3, R = 0.054 ( R w = 0.067), 4592 reflections with I > 3 σ( I)) reveals that the citrate ligands are fully deprotonated and coordinated to the [Mo 2O 2(μ-S 2)] 2+ core via the central and one terminal carboxylate groups and the deprotonated hydroxyl group.

Structures of 1,3-bis(diphenylphosphino)propane platinum(II) alditolate complexes

Single-crystal X-ray diffraction studies have been carried out on three crystalline (dppp)Pt(II)(alditolate) complexes derived from reactions of the sugar alcohols glycerol, erythritol, and galactitol with (dppp)Pt(CO 3). The alditols bind to the platinum via adjacent, deprotonated hydroxyl groups to form a 2,5-dioxaplatinacyclopentane ring system having hydroxyalkyl substituent side-chains. The hydroxyl groups in these side-chains all engage in either intra- or intermolecular hydrogen bonds, the former preferentially involving hydrogen bond donation from a hydroxyl group on the β-carbon of the metallacycle dihydroxyethyl or trihydroxypropyl substituent to either the near or far metallacycle oxygen atoms to give a six- or seven-membered hydrogen-bonded ring system, respectively. Five-membered hydrogen-bonded ring systems to the adjacent metallacycle oxygen are observed for hydroxymethyl side-chains. These hydrogen-bonded interactions are believed to play a significant role in the complexation regioselectivity observed in these alditolate complexes. Conformations of the 2,5-dioxaplatinacyclopentane ring and dppp chelate ring are also discussed, as are comparisons with other alditolate and diolate structural determinations.

Synthesis, characterization, and biological relevance of hydroxypyrone and hydroxypyridinone complexes of molybdenum

We have prepared a number of complexes of the type cis-MoO2L2 where L represents a hydroxypyronato or hydroxypyridinonato ligand. Both the maltol (3-hydroxy-2-methyl-4-pyrone, Hma) and kojic acid (5-hydroxy-2-hydroxymethyl-4-pyrone, Hka) complexes, cis-MoO2(ma)2 (1) and cis-MoO2(ka)2 (2), have been characterized by X-ray diffraction studies. The pyrone ligands are bound to molybdenum in a cis bidentate fashion via the deprotonated hydroxyl groups and the ketone moieties. Crystals of 1 are orthorhombic, a = 12.107 (1), b = 8.6169 (8), c = 16.472 (1) Å, Z = 4, space group Pca21, and those of 2 are monoclinic, a = 8.4591 (5), b = 16.3453 (10), c = 10.2954 (7) Å, β = 103.0320 (10)°, Z = 4, space group P21/c. Hydroxypyridinone molybdenum complexes have been prepared for both maltol and kojic acid derivatives with the substituents Me, n-Pr, CH2Ph, Ph at the ring nitrogen. Crystals of the 3-hydroxy-2-methyl-1-phenyl-4-pyridinone (Hppp) derivative, MoO2(ppp)2 (9), are monoclinic, a = 10.9476 (6), b = 13.5353 (9), c = 17.4877 (10) Å, β = 93.465 (4)°, Z = 4, space group P21/n. Initial investigations into the effects molybdenum compounds have on diabetic hearts are presented. Both Na2MoO4 (used as a control) and 1 were effective in lowering blood glucose and free fatty acid levels. Diabetic rats treated with molybdate showed significant improvements in postischemic cardiac function.Key words: molybdenum, hydroxypyrones, hydroxypyridinones, heart function.

An EPR study of polysaccharide copper(II) complexes in composite dextran/epichlorohydrin gels

The EPR spectra of composite dextran and carboxymethyldextran gels were studied in order to identify the functional groups involved in copper(II) complexation depending on pH. The porous structure resulting from crosslinking of polymer chains of dextran, via epichlorohydrin, forces the immobilization of Cu 2+ ions surrounded by different oxygen groups of the polymer gel matrix. The different polynuclear structures are postulated to be formed depending on the type of polysaccharide derivatives. The results indicate that carboxyl and deprotonated hydroxyl groups participate in the complex formation.

Effects of cyclodextrin on hydrolysis and the Smiles rearrangement of salicylic acid esters

The effect of β-cyclodextrin (β-CD) on “aqueous” hydrolysis of methyl,p-, andm-nitrophenyl salicylates as well as on the Smiles rearrangement ofp-nitrophenyl salicylate was studied. No effect of β-CD on the pH-independent rate constant of “aqueous” hydrolysis of methyl ester was observed, while β-CD accelerated “aqueous” hydrolysis of nitrophenyl esters byca. 10 times. The inclusion of these esters into the cavity of β-CD is accompanied by a change in the mechanism of hydrolysis: free ester in the deprotonated form undergoes hydrolysis through the mechanism of intramolecular general base catalysis, while the ester bound to cyclodextrin is hydrolyzed due to the nucleophilic attack of the deprotonated hydroxyl group of β-CD at a neutral substrate molecule. The effects of cyclodextrin on the rate constant of borate-catalyzed hydrolysis were interpreted by assuming that the substrate bound to β-CD undergoes borate-assisted attack at the deprotonated cyclodextrin hydroxyl group. The Smiles rearrangement, which is an intramolecular nucleophilic substitution reaction, is accelerated in the presence of β-CD.

Solution structures of luminescent chelates of europium (III) with 2,6-bis[ N,N-bis(carboxymethyl) aminomethyl]-4-benzoylphenol

2,6-Bis[ N,N-bis(carboxymethyl)aminomethyl]-4-benzoylphenol forms with europium(III) three structurally different luminescent chelates in aqueous sample solutions. Only the chelate with a dimeric structure, where two Eu(III) cations are encapsulated into the chelating cage consisting of two deprotonated phenolic hydroxyl groups and four 2,2′-(methylenenitrilo)bis(acetic acid) moieties having strong interactions with the deprotonated hydroxyl groups, is capable of initiating the sensitized 5D 0 → 7F j transitions of Eu (III) with an exceptionally long lifetime of 0.97 ms.

X-ray absorption spectroscopic studies of the Fe(II) active site of catechol 2,3-dioxygenase. Implications for the extradiol cleavage mechanism.

The extradiol-cleaving catechol 2,3-dioxygenase (2,3-CTD) isolated from Pseudomonas putida mt-2 and its catechol and ternary E.S.NO complexes are characterized by X-ray absorption spectroscopy (XAS). The intensities of the 1s-->3d transitions in the pre-edge spectra of the uncomplexed enzyme and its substrate complex show that the Fe(II) center is five-coordinate in both complexes, in agreement with earlier magnetic circular dichroism studies [Mabrouk, P. A., Orville, A. M., Lipscomb, J. D., & Solomon, E. I. (1991) J. Am. Chem. Soc. 113, 4053-4061]. Analysis of the EXAFS region of uncomplexed 2,3-CTD shows five N/O ligand atoms 2.09 A from the active site Fe(II). In the 2,3-CTD.catechol complex, one N/O atom is located at 1.93 A and four N/O type ligands are at 2.10 A. By comparison with [FeII-(6TLA)(DBCH)](ClO4), the first well-characterized mononuclear Fe(II).catechol model complex, the 1.93 A scatterer is proposed to be the oxygen from the deprotonated hydroxyl group of the coordinated catecholate monoanion. Nitric oxide binds to the Fe(II) center in the enzyme.catechol complex without displacing the existing ligands, resulting in the formation of a six-coordinate complex, as indicated by the addition of a new N/O type scatterer at 1.74 A. Bond valence sum (BVS) analysis of the bond lengths derived from the EXAFS fits gives values that correspond to the iron oxidation states established for these complexes, thus lending credence to the coordination environment deduced for the iron center in those complexes. The present study provides the first evidence for a monoanionic substrate binding mode in an extradiol dioxygenase, which is distinct from the dianionic binding mode proposed for intradiol dioxygenases. We speculate that this difference in binding mode may have important ramifications for the site of aromatic ring cleavage in the subsequent oxygen insertion reactions.

Studies on a new type of terbium complex with sulphonated catecholate. The molecular structure and fluorescene properties or [Tb 2(C 6H 3S 2O 8) 2·6DMF] n

Reaction of sulphonated catecholate Na 2C 6H 4S 2O 8 (Tiron) and terbium perchlorate with a 3:2 mole ratio in hot water resulted in the precipitation of crystalline Tb 2(C 6H 3S 2O 8) 2·5H 2O ( A) which recrystallized in water-DMF mixed solvent to obtain the title complex Tb 2(C 6H 3S 2O 8) 2·6DMF ( B). The X-ray crystal structure determination of B indicates that Tiron and terbium ion form a chain polymer with a 1:1 mole ratio. The unique structural unit is a dimer in which two terbium ions are bridged by one oxygen atom from a deprotonated hydroxyl group of Tiron. The distance between terbium ions is 3.385 Å. The terbium ion is eight-coordinated dodecahedral. The elemental analysis data and thermographic data show that compound B loses one DMF molecule in air to become Tb 2(C 6H 3S 2O 8) 2·5DMF ( B′). The fluorescence spectra of A and B′ have been studied. Both A and B′ have the same maximum excitation wavelength (318 nm) at which the emission fluorescence intensity of B′ is 2.5 times that of A at 543 nm. The thermogravimetric analysis and IR spectra of A and B′ have been studied.

Copper(II) and oxovanadium(IV) complexes of ?-hydroxymethylserine

Potentiometric and spectroscopic measurements were used to characterize the binding ability of α-hydroxy-methylserine (Hms) with copper(II) and oxovanadium(IV) ions. The ligand was found to be generally a more efficient chelating agent than serine. Both of the deprotonated hydroxyl groups of Hms can be involved in coordination to vanadyl ions, whereas copper(II) binds in the same way as with serine.

Photophysical Probes of a Protein/Semiconductor Electrode Interface

Immobilization of redox molecules on solid electrodes offers a way of investigating the electron transfer of a donorlacceptor interface without the presence of diffusion processes.‘ Such interactions also have important implications for analytical and clinical biochemistry. Direct electrochemistry of proteins and enzymes is therefore an active research field.2 One example of direct protein electrochemistry relevant to this work is cytochrome c (Cyt c ) adsorbed on a tin oxide (SnO2) surface.lb This protein is rich in lysine amino acid residues and thus carries positive charges at neutral pH. It has been found that the native protein, Fe-Cyt c, adsorbs strongly on SnO2, presumably through the electrostatic interaction with the deprotonated hydroxyl groups on SnOz surface (Scheme 1A). The electron transfer rate constant between the two at zero free energy has been measured by cyclic voltammetry and is found to be relatively slow (3-8 s-l). In terms of modern theoretical understanding of electron transfer? the parameters (electronic coupling, V, and reorganization energy, A) which govern this rate remain uncharacterized. We report here a novel approach to obtain such parameters by combining thermal and photochemical interfacial electron transfer measurements within the context of a novel theoretical formalism. We used time-resolved fluorescence spectroscopy to measure the interfacial electron transfer rate constant from zinc-substituted cyt c (Zn-Cyt c) to SnOz and estimated electronic coupling between the protein and semiconductor and the reaction reorganization energy. The lowest photoexcited state of Zn-Cyt c has a much higher energy level4 than the conduction band edge5 of SnO2 (Scheme IB). Electron injection to SnO2 (route a in Scheme 1B) is therefore a thermodynamically favorable process that competes with fluorescent decay emission (route b). Zn-Cyt c was prepared6 and adsorbedlbs7 onto a fluorinedoped SnO2 substrate according to the published procedures. The adsorption was confirmed by the UV-vis spectrum of ZnCyt c and cyclic voltammogram of the native Fe-Cyt c. Integration of either the anodic or the cathodic wave in the voltammogram yielded a surface coverage of 510 pmol/cm2, which is substantially less than the calculated full monolayer coverage of about 20 pmol/cm2, by assuming the diameter of

Co-ordination of copper(II) with monoamino-triols and -tetrols. Effect of stereochemistry on complex formation

A series of 4-aminobutanetriols and 5-aminopentanetetrols was synthesised and their co-ordination abilities towards copper(II) studied by potentiometry and spectroscopic techniques (UV/VIS, ESR and CD). The basic binding mode involves the amino nitrogen and the adjacent deprotonated hydroxyl group. The latter donor acts as a bridge between two metal ions giving stable dimeric species. No monomeric complexes were detected in the systems studied. The formation of the alkoxo-bridged complexes seems to be the most characteristic feature of the investigated ligands. Other hydroxyl donors are also involved in the metal-ion binding. The stability constants calculated from the pH-metric data showed that the chirality of the carbons in an aminoalcohol molecule may have a considerable effect on its co-ordination ability.

Ethylendiamin-kupfer(II)-komplexe mit polyolat-ionen aus rac-trans-cyclohexan-1,2-diol, erythritol und methyl-α- d-mannopyranosid. Herstellung und kristallstrukturen von [(ethylendiamin)Cu(C 6H 10O 2)] · H 2O, [(μ-ethylendiamin){Cu 2(ethylendiamin) 2(μ′- meso-butantetraolat(4 −))}] · 8H 2O und [(ethylendiamin)Cu(α- d-man pOMeH [2,3]2−2)] · 2H 2O

The ethylenediamine-copper-polyolate complexes [(ethylenediamine)Cu(C 6H 10O 2)]·H 2O ( 1), [(μ-ethylenediamine){Cu 2(ethylenediamine) 2(μ′- meso-butanetetraolate(4 − ))}]·8H 2O ( 2), and [(ethylenediamine)Cu-(methyl α- d-mannopyranosid-2,3-ate(2 −))]·2H 2O ( 3), were formed as violet to blue crystals by the reaction of aqueous ethylenediamine, cupric hydroxide, and the polyol rac-trans-cyclohexane-1,2-diol, erythritol, or methyl α- d-mannopyranoside, respectively. The structures of the coordination compounds have been determined by X-ray crystallography. The number of deprotonated OH groups of the polyols is equal to the stoichiometric amount of OH − ions present in the solution. The respective deprotonated polyols bind as chelate ligands to copper(II) ions. In all three structures, the deprotonated hydroxyl groups are acceptors of asymmetric hydrogen bonds. In 1 and 3, the coordination geometry of copper is square planar (CuO ≈ 193, CuN ≈ 200 pm) with additional aqua ligands at a longer distance (> 280 pm). The square pyramidal complex 2 (193, 204, and 240 pm for CuO, CuN e, and CuN a, respectively) crystallizes from solutions with excess ethylenediamine; the compound is a polymer due to bridging ethylenediamine and erythritol ligands. The structures of the new compounds are discussed in context to cellulose copper complexes in the cellulose solvents Cuoxam and Cuen.

Intramolecular alkoxide induced heterolysis of perhydronaphthalene-1,4-diol monosulfonate esters through orbital interactions over three carbon-carbon single bonds

The course of the reactions that occur when stereochemically rigid trans-perhydronaphthalene1,4-diol monosulfonate esters (1-0) are treated with alkali metal tert-amylate in refluxing benzene depends on the relative orientation of the leaving group and the tertiary hydroxyl group. An equatorial sulfonate ester group favors homofragmentation leading to the cyclopropane derivative 15. In case of an axial sulfonate ester group β-elimination, which strongly depends on the stereochemistry of the tertiary deprotonated hydroxyl group, is the main reaction path

Beryllium Coordination to Bio-Ligands: Isolation from Aqueous Solution and Crystal Structure of a Hexanuclear Complex of Be2+ with Glycolic Acid, Na4[Be6(OCH2CO2)8

Beryllium and its compounds are highly toxic to most living cells, but the mechanisms of the interference with the biological substrates on the molecular level is not understood. From observations in (attempted) chemotherapy of beryllium poisoning using a variety of complexing agents it has been concluded that Be2+ is interacting predominantly with carboxyl as well as hydroxyl functions of protein bio-polymers, with complete deprotonation of the alkoxy or phenoxy functions involved. As a first support for this hypothesis, an analytically well-defined beryllium complex of glycolic acid has now been isolated from aqueous solutions under nearphysiological conditions, crystallized and its structure determined by X-ray diffraction. The hexanuclear complex features beryllium in two different environments, mono- and bis-chelated by glycolate ligands with deprotonated hydroxyl groups. In 9Be-NMR studies of aqueous solutions of the complex (pH 6) the persistence of complexation in two different environments of Be2+ could also be confirmed. The new structure may serve as a model for beryllium complexation with larger bio-ligands.

Bismuth(III) Complexes from Glycol and α-Hydroxycarboxylic Acids

Abstract The reaction of Bi2O3 with mandelic acid (mand H2) resulted in the 2:1 complex [(mandH)2Bi(μ-O)Bi(mandH)2], 1, where only the carboxylato group of the ligand is deprotonated. On the other hand, Bi2O3 when allowed to react with glycolic acid (glycH2), forms the 1:1 Bi:glyc [(μ.-η2-glyc)Bi(μ4-O)Bi(μ-η2-glyc)]∞ complex, 2, in which the ligand shows an unusual mode of bonding involving both the carboxylate oxygen and the deprotonated hydroxyl group of the glycolate; the synthesis and characterization of the ethyleneglycol (EGH2) derivative [Bi4(μ-ηl-EGH)2(μ4-η2-EG)(μ2-η2-EG)4]∞, 3, was undertaken to support our conclusions concerning compound 2.

Thermodynamic Modelling of the Effect of Hydroxycarboxylic Acids on the Solubility of Plutonium at High pH

ABSTRACTA number of the hydroxycarboxylic acids generated by the alkaline degradation of cellulosic wastes under reducing conditions in a cementitious repository can significantly increase the solubility of the actinides at high pH, especially plutonium. The solubility of plutonium at pH 12, in the presence of a range of hydroxycarboxylic acids containing a number of hydroxyl groups and between one and three carboxylate groups, has been modelled using the HARPHRQ code. All the plutonium-organic complexes assumed in the model are based on a stable unit in which a central plutonium ion is bound by four oxygen atoms. The oxygen atoms can be provided either by a deprotonated hydroxyl group on one of the ligands, or by hydroxide ions.

D-Glucosamine Sorption on Cu(II)-Montmorillonite as the Protonated and Neutral Species

AbstractThe adsorption of D-glucosamine (2-amino-2-deoxy-D-gIucose) in the protonated or neutral form on homoionic Cu2+-bentonite was investigated by infrared (IR) and electron spin resonance (ESR) spectroscopy and chemical analyses of solution. The results show that the interaction of the glucosamine hydrochloride with the clay complexed a small fraction of interlayer metal ions with neutral amino sugar molecules. In contrast, the adsorption of free glucosamine was much more favorable and resulted in interlayer copper(II) complexes, mainly those in which the ligand was coordinated through amino and deprotonated hydroxyl groups. Part of the amino sugar molecules, however, were transformed into glucosammonium, replacing copper as the saturating ion.

Spectrophotometric study of complex formation in copper(II) mono-, di-, and tri-ethanolamine systems

The complex formation between CuII and mono-, di-, or tri-ethanolamine, NH3 –nRn(R = CH2CH2OH, n= 1–3), has been studied using visible spectroscopy at ionic strength 1.0 mol dm–3 and 25 °C. Ehanolamines are found to act as multidentate ligands through amino, hydroxyl, and deprotonated hydroxyl groups. The formation constants and the individual spectra of all the complex species detected between pH 2 and 12 have been obtained by least-squares fit of visible spectrophotometnc titration data. As an essential aid to understanding the copper(II)–triethanolamine system, the power of u.v.–visible spectrophotometry to distinguish between monomer and dimer species was especially studied. Two new soluble complex species were identified in this system.