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PubMed2001

Linkage and redox isomerism in ruthenium complexes of catecholate, semi-quinone, and o-acylphenolate ligands derived from tri- and tetrahydroxy-9,10-anthracenediones.

The complexes Ru(CO)(2)L(2)(PHAQ-2H) (PHAQ = 1,2,4-trihydroxy-9,10-anthracenedione (PUR), 1,2,3- trihydroxy-9,10-anthracenedione (AG), and 1,2,5,8-tetrahydroxy-9,10-anthracenedione (QAL); L = PPh(3), PCy(3), PBu(3)), and Ru(CO)(dppe)(PBu(3))(PHAQ-2H), containing catecholate-type ligands were prepared. The complex Ru(CO)(2)(PBu(3))(2)(AG-2H) crystallizes in the space group P2(1)/n (No. 14 var) with a = 13.317(2), b = 15.628(2), c = 21.076(3) A, beta = 101.660(10) degrees, Z = 4; the crystal structure shows it to contain a 2,3-catecholate ligand. The electrochemistry of these complexes was examined, and the semi-quinone complexes [Ru(CO)(2)L(2)(PHAQ-2H)](1+) and [Ru(CO)(dppe)(PBu(3))(PHAQ-2H)](1+) were generated by chemical oxidation. One example of an o-acylphenolate complex, HRu(CO)(PCy(3))(2)(PUR-H), is also reported.

Journal Article↗
PubMed2002

Kinetic study of the oxidation of catechol by aqueous copper(II).

The kinetics of the oxidation of catechol by aqueous copper(II) have been studied as a function of reactant concentrations at pH 6.4-7.2. To follow the reaction, a spectrophotometric method has been developed that circumvents the problem of precipitation of decomposition products of the initial o-quinone oxidation product. The rate law shows that the reactive species is the monocatecholate complex of Cu(II), and that this species undergoes rate-limiting intramolecular electron transfer with k = 1.9 x 10(-5) s(-1) (22 +/- 1 degrees C, mu = 0.125 M NaClO(4)). The results have allowed a reanalysis of previous work on the autoxidation in the aqueous Cu(II)-catechol-dioxygen system, and comparisons to mechanisms of copper(II) oxidases.

Journal Article↗
PubMed2005

Effects of countercations on the structures and redox and spectroscopic properties of diruthenium catecholate complexes with ligand-unsupported Ru-Ru bonds.

The molecular structures and physicochemical properties of diruthenium complexes with ligand-unsupported Ru-Ru bonds, generally formulated as [A2{Ru2(DTBCat)4}] (DTB = 3,5- or 3,6-di-tert-butyl; Cat(2-) = catecholate), were studied in detail by changing the countercations. First, the binding structures of the cations in a family of [{A(DME)n}2{Ru2(3,5-DTBCat)4}] (n = 2 for A+ = Li+ and Na+ and n = 1 for A+ = K+ and Rb+) were systematically examined to reveal the effects of the cations on the molecular structures and electrochemical properties. Second, the complex (n-Bu4N)2[Ru2(3,6-DTBCat)4] with a cation-free structure was synthesized using tetra-n-butylammonium cations. The complex clearly demonstrates first that the ligand-unsupported Ru-Ru bonds are essentially stabilized by the dianionic nature of the catecholate derivatives without any other bridging or supporting species. In contrast, the redox potentials and absorption spectra of the complexes can sensitively respond to the countercations depending upon the polarity of the solvents.

Journal Article↗
PubMed2005

Substituent-directed structural and physicochemical controls of diruthenium catecholate complexes with ligand-unsupported Ru-Ru bonds.

A family of diruthenium complexes with ligand-unsupported Ru-Ru bonds has been systematically synthesized, and their crystal structures and physical properties have been examined. A simple, useful reaction between Ru2(OAc)4Cl (OAc- = acetate) and catechol derivatives in the presence of bases afforded a variety of diruthenium complexes, generally formulated as [Na(n){Ru2(R4Cat)4}] (n = 2 or 3; R4 = -F4, -Cl4, -Br4, -H4, -3,5-di-t-Bu, and -3,6-di-t-Bu; Cat(2-) = catecholate). The most characteristic feature of the complexes is the formation of short ligand-unsupported Ru-Ru bonds (2.140-2.273 A). These comprehensive studies were carried out to evaluate the effects of the oxidation states and the substituents governing the molecular structures and physicochemical properties. The Ru-Ru bond distances, rotational conformations, and bending structures of the complexes were successfully varied. The results presented in this manuscript clearly demonstrate that the complexes with ligand-unsupported Ru-Ru bonds can sensitively respond to redox reactions and ligand substituents on the basis of the greater degree of freedom in their molecular structures.

Journal Article↗
PubMed2005

Binuclear complexes of Co(III) containing extended conjugated bis(catecholate) ligands.

Binuclear complexes of cobalt(III) have been prepared with 3,3',4,4'-tetrahydroxy-benzaldazine (H4thB), 3,3',4,4'-tetrahydroxy-5,5'-dimethoxybenzaldazine (H4thM), and 3,3',4,4'-tetrahydroxydimethylbenzaldazine (H4thA) as bis(catecholate) ligands that link metal ions separated by 16 A through a conjugated bridge. In one case, [Co2(bpy)4(thM)]2+, stereodynamic properties observed in solution by 1H NMR are associated with valence tautomerism, with formation of a labile hs-Co(II) species by electron transfer from the catecholate regions of the bridge. Electrochemical oxidation of the complexes occurs at the bridges as two closely spaced one-electron couples. Chemical oxidation of [Co2(bpy) 4(thB)]2+ with Ag+ is observed to occur as a two-electron process forming [Co2(bpy) 4(thB(SQ,SQ))]4+. Attempted crystallization in the presence of air was observed to result in formation of the [Co(bpy)2(BACat)]+ (H2BACat, 3,4-dihydroxybenzaldehyde) cation by aerobic oxidation. Structural characterization is provided for the H4thM ligand and [Co(bpy)2(BACat)](BF4).

Journal Article↗
PubMed1998

Structure-Reactivity Relationships for Associative Displacement Reactions of Penta- and Hexacoordinate Cyclic Oxyphosphoranes with Catechols(1)(,)(2).

The reactivity of a series of cyclic pentaoxyphosphoranes containing a sulfonyl group was carried out, O(2)S[(t-Bu)MeC(6)H(2)O](2)P(OCH(2)CF(3))(3) (1), O(2)S[(t-Bu)MeC(6)H(2)O](2)P(OPh)(3) (2), O(2)S[(t-Bu)(2)C(6)H(2)O](2)P(OCH(2)CF(3))(3) (4), and O(2)S[(t-Bu)(2)C(6)H(2)O](2)P(OPh)(3) (5). Also included were derivatives containing sulfur, S[(t-Bu)MeC(6)H(2)O](2)P(OPh)(3) (6) and S[(t-Bu)(2)C(6)H(2)O](2)P(OPh)(3) (8), and the methylene group, CH(2)[(t-Bu)MeC(6)H(2)O](2)P(OPh)(3) (7), in place of the sulfonyl group in the ring-containing component. (31)P NMR monitoring of the reactions of the oxyphosphoranes with catechol and 4-nitrocatechol shows the following order of reactivity: 7 > 8 > 6 > 2 > 5 >> 1. It is established that the reactions are associative. An analysis of the products formed is given relative to this mechanistic process. Both 1 and 4 are found to be inert toward nucleophilic displacement by the catechols employed. It is suggested that the looseness of P-O bonds (implied by their increased length) that reside in either octahedral formulations or in axial positions of a trigonal biyramid is the principal factor associated with reactivity for these cyclic oxyphosphoranes. For the hexacoordinated geometries, the order of reactivity parallels the extent of octahedral character: 8 > 6 > 2 > 5.

Journal Article↗
PubMedDate not supplied

Pentadentate terpyridine-catechol linked ligands and their cobalt(III) complexes.

A series of novel pentadentate terpyridine-catechol linked ligands were prepared, in which the terpyridine and catechol moieties were linked together by (CH2)n chains of different lengths (n = 4-6). Together with 1-methylimidazole, these ligands formed low-spin, six-coordinate Co(III) complexes. Two of the complexes (n = 4, 5) were characterized by X-ray crystallography [n = 4, monoclinic, P2(1)/c, a = 14.957(7) A, b = 10.585(9) A, c = 23.033(7) A, beta = 106.01(3) degrees, V = 3505(3) A3, Z = 4, R = 0.063; n = 5, monoclinic, P2(1)/c, a = 8.848(7) A, b = 15.78(1) A, c = 25.455(7) A, beta = 93.90(5) degrees, V = 3544(3) A3, Z = 4, R = 0.056], which revealed similar structures around the Co(III) centers but different conformations for the (CH2)n linkers. The (CH2)4 linker showed a straight, symmetric conformation whereas the (CH2)5 linker showed a curved conformation that allowed the accommodation of one extra CH2 unit, suggesting that the (CH2)4 linker presents the "best-fit" length for these complexes.

Journal Article↗
PubMed2002

The role of hydrogen bonding on the h-atom-donating abilities of catechols and naphthalene diols and on a previously overlooked aspect of their infrared spectra.

Catechols and 1,8-naphthalene diols contain one "free" hydroxyl and one intramolecularly H-bonded hydroxyl group. The "free" hydroxyls are strong hydrogen-bond donors (HBDs) with alpha2H values (Abraham et al. J. Chem. Soc., Perkin Trans. 2 1989, 699) ranging from 0.685 to 0.775, indicating that these compounds have similar HBD properties to those of strongly acidic phenols such as 4-chlorophenol (alpha2H = 0.670) and 3, 5-dichlorophenol (alpha2H = 0.774). Kinetic effects on H-atom abstractions from the diols in HB acceptor (HBA) solvents can be quantitatively accounted for over at least 50% of the available range of solvent HBA activities (as measured by their beta2H values; see Abraham et al. J. Chem. Soc. Perkin Trans. 2 1990, 521) on the basis of a single reactive OH group, the "free" OH. This free OH group is an outstanding H-atom donor in poor HBA solvents; e.g., in hexane rate constants for reaction with the DPPH* radical are 2.1 x 104 M-1 s-1 for 3,5-di-tert-butyl catechol and 2 x 106 M-1 s-1 for 4-methoxy-1,8-naphthalene diol, but only 7.4 x 103 M-1 s-1 for alpha-tocopherol (vitamin E). The diols are much more reactive than simple phenols because the O-H bond dissociation enthalpy of the "free" OH group is weakened by 5-9 kcal/mol by the intramolecular H-bond. The IR spectra of all the diols in CCl4 show two fairly sharp O-H stretching bands of roughly equal intensity separated by 42-138 cm-1. Addition of a low concentration of DMSO, a strong HBA, causes the band due to the intramolecularly H-bonded OH group to decrease in intensity to roughly half the extent that the "free" OH band loses intensity. The latter forms an intermolecular H-bond with the DMSO, the former does not. What has been overlooked in earlier work is that as the DMSO concentration is increased the band due to the intramolecularly H-bonded OH group first broadens and then evolves into a new, lower frequency (by 19-92 cm-1) band. The magnitude of the shift in the frequency of the intramolecular OH band caused by H-bonding of HBAs to the "free" OH group, Deltanu, increases linearly as the HBA activity of the additive increases, e.g., for 3,5-di-tert-butylcatechol, Deltanu/cm-1 = 33.8 beta2H (R 2 = 0.986). This may provide a new and simple method for determining beta2H values.

Journal Article↗
PubMed1987

Synthesis and evaluation of non-catechol D-1 and D-2 dopamine receptor agonists: benzimidazol-2-one, benzoxazol-2-one, and the highly potent benzothiazol-2-one 7-ethylamines.

Our interest in identifying D-1 and D-2 dopamine receptor agonists that are not catechols led us to extend previous studies with oxindoles by investigating analogues of dopamine, N,N-dipropyldopamine, m-tyramine, N,N-dipropyl-m-tyramine, and epinine in which the m-hydroxyl is replaced by the NH portion of a thiazol-2-one, oxazol-2-one, or imidazol-2-one group fused to the 2,3-position. These compounds were evaluated for their affinity and agonist activity at D-1 and D-2 receptors by using in vitro assays. Replacement of the m-hydroxy in N,N-dipropyldopamine with the thiazol-2-one group resulted in a dramatic increase in D-2 receptor affinity and activity compared to that of N,N-dipropyldopamine itself or that of the corresponding oxindole, 1. The resulting compound, 7-hydroxy-4-[2-(di-n-propylamino)ethyl]benzothiazol-2(3H)-one (4), is the most potent D-2 receptor agonist reported to date in the field-stimulated rabbit ear artery (ED50 = 0.028 nM). The benzoxazol-2-one (6), benzimidazol-2-one (5), and isatin (51) analogues showed D-2 receptor agonist potency similar to that of 1. The des-7-hydroxyl analogue of 4 (21) also has enhanced D-2 receptor activity compared to that of the corresponding oxindole, 8. 7-Hydroxy-4-(2-aminoethyl)benzothiazol-2(3H)-one, 27, a non-catechol, has enhanced D-1 and D-2 receptor activity in vitro compared to that of the corresponding oxindole, 7. In vivo, 27 increased renal blood flow and decreased blood pressure in the dog. However, these effects were mediated primarily by D-2 receptor agonist activity. This may be a result of the D-1 partial agonist activity of 27 coupled with its potent D-2 receptor activity.

Animals↗
PubMed2006

Thermally stable amorphous mesoporous aluminophosphates with controllable P/Al ratio: synthesis, characterization, and catalytic performance for selective O-methylation of catechol.

Amorphous mesoporous aluminophosphates (AlPO) with P/Al molar ratio in the range 0.8-1.15 are synthesized by using the citric acid (CA) route and are systematically characterized using N(2)-adsorption, XRD, SEM, solid-state CP-MAS NMR, FT-IR, TG-DTA, CO(2)-TPD, and NH(3)-TPD. The characterization studies show that the change in P/Al ratio could affect the structure, texture, thermal stability, and surface acid-base properties of AlPO. Samples with a relatively low P/Al ratio (< or =1.0) exhibit uniform amorphous mesoporous character and high thermal stability (up to 1173 K). Partial crystallization of the AlPO framework easily occurred on the sample with higher P/Al ratio (> or =1.1), thus leading to significant decrease of surface area and formation of particle pile mesopores. Both weak acid and weak base sites are observed over AlPO materials, and the amounts of acid-base sites can be effectively controlled by adjusting the P/Al ratio. The presence of suitable interaction between citric acid and AlPO framework is critical for the formation of mesoporous structures. Both CA and PO(4) units are considered to be ligands to coordinate with aluminum ions, forming relative uniform complexes (such as CA-Al-PO(4)) in the as-synthesized AlPO materials. The mesoporous structure of AlPO materials is obtained after the rapid decomposition of citric acid. Vapor phase selective O-methylation of catechol with methanol reaction is carried out to investigate the catalytic performances of AlPO materials with different P/Al ratios. Among them, AlP(1.1)O shows the highest activity (88.4% conversion of catechol) and the highest yield of guaiacol (74.3%). The presence of suitable weak acid-base pairs may play an important role on the title reaction.

Journal Article↗
PubMed2005

Interaction of catechol and gallic acid with titanium dioxide in aqueous suspensions. 1. Equilibrium studies.

The adsorption isotherms of catechol (1,2-dihydroxybenzene) and gallic acid (3,4,5-trihydroxybenzoic acid) onto titanium dioxide (Degussa P-25) were measured at various pH values and room temperature using attenuated total reflection Fourier transform infrared (FTIR-ATR) data, processed by singular value decomposition. The affinity is largely pH independent, although the deprotonatation of the carboxylic group in gallic acid might produce a slight increase in the affinity. Catechol was shown to form two complexes, with Langmuir stability constants log K of 4.66 (strong mode) and 3.65 (weak mode). Both complexes have the same spectral signature, and mononuclear and binuclear chelate structures are proposed for them. Gallic acid chemisorbs by complexation through two -OH groups and forms one complex only, log K = 4.70. The third -OH and the pendant carboxylate do not influence much the stability of the surface complex. Comparison with literature data demonstrates that the affinity of 4-chlorocatechol is also similar, whereas 2,3-dihidroxynaphthalene and 4-nitrocatechol form more stable complexes, probably because of the solvation contribution to the overall Gibbs adsorption energy. All quoted constants refer to the surface complexation equilibria written as follows: ([triple bond]Ti-OH)2 + H2L = ([triple bond]Ti)2-L + 2H2O, i.e., as electroneutral processes. The FTIR-ATR spectra of the surface complexes are also discussed.

Journal Article↗
PubMed2004

Palladium-catalyzed cross-coupling of aryl triethylammonium bis(catechol) silicates with aryl bromides using microwave irradiation.

The scope of the palladium-catalyzed cross-coupling reaction of aryl bis(catechol) silicates has been extended to include the coupling of aryl bromides by employing microwave irradiation. This new set of coupling conditions is tolerant of electron-rich and -deficient aryl bromides. In addition, a variety of substituted aryl bis(catechol) silicates have been successfully cross-coupled.

Bromides↗
PubMed2005

Palladium(II)-catalyzed oxidative transformation of allylic alcohols and vinyl ethers into 2-alkoxytetrahydrofurans: catechol as an activator of catalyst.

[chemical reaction: see text]. A highly effective synthesis of 2-alkoxytetrahydrofurans from allylic alcohols and vinyl ethers was achieved by using catalytic amounts of Pd(OAc)2, Cu(OAc)2, and catechol (1:1:2) under O2. The use of catechol as an activator of Pd(II)-Cu(II) catalyst has been unprecedented. The 2-alkoxytetrahydrofurans are formed via oxypalladation of allylic alcohols toward vinyl ethers followed by 5-exo cyclization of the resulting oxypalladation intermediate and subsequent beta-Pd-H elimination. No 6-endo cyclization of the oxypalladation intermediate occurs.

Journal Article↗
PubMed2004

Fe(III)-EDTA complex abatement using a catechol driven Fenton reaction combined with a biological treatment.

A combined chemical oxidation (catechol-driven Fenton reaction) followed by a biological treatment was used to degrade Fe(III)-EDTA (1.34 mM). The chemical treatment was inspired in fungal non-enzymatic wood rot mechanisms that use dihydroxybenzens in order to promote the Fenton reaction to breakdown wood structures. This chemical pre-oxidation used catechol (50 microM) and H202 (20 mM) and the reaction products were identified by GC-MS. In addition, a biological treatment was coupled using the baker's yeast Saccharomyces cerevisiae. The combined chemical biological treatment achieved 100% EDTA degradation, 68 % total organic carbon removal and 90% iron removal.

Biodegradation, Environmental↗
PubMed1994

DNA damage caused by reactive oxygen species originating from a copper-dependent oxidation of the 2-hydroxy catechol of estradiol.

It has previously been proposed that redox cycling between catechol estrogens and their quinones, mediated by cytochrome P450, could lead to the generation of free radicals that would subsequently cause oxidative damage to DNA and proteins that might have a role in hormonal carcinogenesis. Alternative, non-enzymatic mechanisms involving copper have been shown to participate in the oxidation of various chemicals through processes that also result in the appearance of reactive oxygen species and subsequent site-specific oxidative DNA damage. The goal of the present study was to determine whether the 2-hydroxy-catechol of estradiol (2-OH-E2) can be oxidized by copper through a process which generates reactive oxygen species that cause oxidative DNA damage as detected by the appearance of strand breaks in phi X-174 plasmid DNA. Our results show that both single- and double-strand breaks are formed in the presence of Cu(II) plus micromolar concentrations of 2-OH-E2, and 4-OH-E2, in a concentration/time-dependent process. No strand breaks were detected in the presence of Cu(II) or 2-OH-E2 alone. The reaction of 2-OH-E2 with Cu(II) was accompanied by the reduction of Cu(II) to Cu(I), the utilization of O2, and the generation of H2O2. The utilization of O2 and the formation of strand breaks was completely blocked by the Cu(I)-specific chelator bathocuproinedisulfonic acid (BCS) at a ratio of BCS to Cu(II) of 4:1. The appearance of strand breaks was also blocked by catalase and inhibited by the singlet oxygen scavengers sodium azide and 2,2,6,6-tetramethyl-4-piperidone. In contrast the free hydroxyl radical scavengers mannitol and N-tert-butyl-alpha-phenylnitrone were not effective inhibitors; superoxide dismutase had no inhibitory effect. These results are similar to what has been observed by others for the formation of oxidative DNA damage by the H2O2/Cu(II) system and by us for the induction of strand breaks by hydroquinone/Cu(II). Since copper is known to be present in the nucleus, particularly in association with guanines in DNA, our results with 2-OH-E2/Cu(II) together with those of others with H2O2/Cu(II), discussed below, suggest an alternate site-specific mechanism for the formation of oxidative DNA damage associated with estrogen treatment. Furthermore, the results suggest that the oxidative damage results from the localized generation of singlet oxygen or a similar bound reactive entity rather than free hydroxyl radical.

Copper↗
PubMed1993

Interindividual variability of phenol- and catechol-sulphotransferases in platelets from adults and newborns.

1 Phenol- and catechol- sulphotransferase activities were measured with p-nitrophenol and dopamine as substrates in platelets obtained from 100 newborns and 100 healthy adults. 2 Mean +/- (s.d.) estimates of catechol sulphotransferase activity were 7.07 +/- 5.93 (adult) and 13.3 +/- 6.42 (newborn) pmol min(-1) mg(-1) protein, respectively (P < 0.001). The coefficients of variation were 84% (adult) and 48% (newborn). The frequency distribution of sulphotransferase activity was symmetric and did not deviate significantly from normality in newborn platelets, but was positively skewed in adult platelets. 3 Mean +/- (s.d.) estimates of phenol sulphotransferase activity were 3.01 +/- 3.21 (adult) and 4.80 +/- 4.34 (newborn) pmol min(-1) mg(-1), respectively (P < 0.001). The coefficients of variation were 107% (adult) and 90% (newborn). The frequency distribution of sulphotransferase activity was positively skewed in both newborn and adult platelets. 4 Since sulphotransferase activity in platelets is well-expressed at birth and a prenatal development of sulphotransferase has been described in mid-gestational human foetal liver, the newborn should be able to sulphate drugs.

Adult↗
PubMed1986

Non involvement of gamma-aminobutyric acid in catechol-induced seizures.

The effects of certain anticonvulsant agents, namely, valproate, diazepam and phenobarbitone were investigated on catechol-induced spontaneous and evoked convulsions, in anaesthetized rats and mice. Valproate and diazepam significantly reduced the intensity of spontaneous convulsions and the frequency of occurrence of the longer-latency components (M2 and M3) of the evoked muscle response. Phenobarbitone significantly reduced spontaneous convulsions and the M3 component of the evoked muscle response. None of the drugs affected the short latency M1 component indicating a supra-spinal site of action of these drugs. Agents which modify gamma-aminobutyric acid (GABA)-mediated transmission were without effect on the frequency of occurrence of M1, M2 or M3. The results suggest that the convulsant action of catechol is not dependent on antagonism of GABA-mediated inhibition.

Animals↗
PubMed1991

In vitro evaluation of GR69153, a novel catechol-substituted cephalosporin.

GR69153 is a C-7 catechol cephalosporin with a broad spectrum of activity against members of the family Enterobacteriaceae (MICs for 50% of strains tested [MIC50s], 0.008 to 0.5 micrograms/ml), Staphylococcus aureus (MIC50, 4 micrograms/ml), Pseudomonas aeruginosa (MIC50, 0.25 micrograms/ml), Haemophilus influenzae (MIC50, 0.03 micrograms/ml), Neisseria gonorrhoeae (MIC50, 0.03 micrograms/ml), and Acinetobacter spp. (MIC50, 2 micrograms/ml). Potent GR69153 activity was also demonstrated against Moraxella catarrhalis, pneumococci, beta-hemolytic streptococci, gram-positive anaerobes, and most species of coagulase-negative staphylococci. The activity of GR69153 was generally two- to fourfold greater than that of ceftazidime. Resistance level GR69153 MICs for 90% of strains tested (greater than or equal to 32 micrograms/ml) were found most often among Citrobacter freundii, Enterobacter spp. and Morganella morganii strains. GR69153 did not significantly inhibit enterococci, Xanthomonas maltophilia, the Bacteroides fragilis group, Corynebacterium jeikeium, or Listeria monocytogenes. GR69153 was bactericidal and was generally beta-lactamase stable, and MICs were only slightly increased by high inoculum concentrations. Activity was enhanced in an iron-deficient medium, and a modest MIC difference attributed to iron availability was noted between standard agar and broth test results. GR69153 was confirmed to be a potent, catechol-substituted cephalosporin with a spectrum slightly wider than that of ceftazidime, but it was less active than cefpirome or imipenem against some gram-positive pathogens and anaerobes.

Bacteria↗