Catechol System Research Articles

Electrochemistry of Al3+- Catechol System: Kinetics Vs. Thermodynamics (A1-Triple I)

Carbonyls, and quinones among them in particular, occupy a place of choice among organic reversible redox systems for electrocatalysis [1] and energy storage [2]. Their electrochemical behavior is marked by coupled proton and electron transfer (CPET) [3-5]. We have studied this subject in the context of flow batteries [6] and hydrogen carriers [7]. On the other hand, metal ion – catecholate (o-dioxolene) binding [8] attracts attention in different and rather independent domains, including active materials for metal-ion and redox flow batteries [2]. Redox transformations of o-dioxolene-metal complexes are therefore coupled to competitive binding with metal ion and proton at the electrochemical timescale, raising the complexity in the system above that of CPET. These effects have not received proper attention e.g. in aqueous metal-ion battery research.The subject of this communication is the electrochemistry of Al3+ - catechol system in aqueous solution. We discuss the conditions and measurable electrochemical signatures of complex formation, as well as the role of buffer. We explain why our observations are contrasting those on catechol containing polymers proposed for universal metal-ion batteries [9, 10] by considering which reactions attain equilibrium and which are obeying kinetics only.[1] K. Tammeveski et al. J. Electroanal. Chem. 2001, 515 , 101; DOI: 10.1016/S0022-0728(01)00633-7[2] B. Häupler et al. Adv. Energy Mater. 2015, 5 , 1402034; DOI: 10.1002/aenm.201402034[3] M. Quan et al. J. Am. Chem. Soc. 2007, 129 , 12847; DOI: 10.1021/ja0743083[4] J. Wang et al. J. Electroanal. Chem. 2007, 601 , 107; DOI: 10.1016/j.jelechem.2006.10.036[5] Q. Lin et al. J. Phys. Chem. C 2015, 119 , 1489; DOI: 10.1021/jp511414b[6] H. Ghorbani Shiraz et al. J. Energy Chem. 2022, 73 , 292; DOI: 10.1016/j.jechem.2022.06.015[7] M. Vagin et al. Adv. Funct. Mat. 2020, 30 , 2007009; DOI: 10.1002/adfm.202007009[8] R. Maskey et al. Encycl. Inorg. Bioinorg. Chem.; DOI: 10.1002/9781119951438.eibc2810[9] N. Patil et al. ACS Appl. Energy Mater. 2019, 2, 3035; DOI: 10.1021/acsaem.9b00443[10] K. Pirnat et al. Macromolecules 2019, 52, 8155; DOI: 10.1021/acs.macromol.9b01405

Synthesis and chiroptical properties of inherently chiral ‘picket-fence’ catechol BOPHYs

Chiral bis-N,N,O,O-boron chelated BOPHY dyes are produced in a one-pot reaction of (1E,2E)-1,2-bis((3,5-dimethyl-1H-pyrrol-2-yl)methylene)hydrazine, boron tribromide, and an unsymmetrically substituted catechol derivative. Remarkably, in the case of methyl 2,3-dihydroxybenzoate the chiral, racemic diastereoisomeric bis-boron chelate is formed with complete stereoselectivity. In contrast, the corresponding reaction with 3,5-di-tert-butylcatechol produces a 3:1 ratio of racemic and meso (achiral) diastereoisomers. These boron chelates display two strong (ε 33–41,000 M−1 cm−1) absorption maxima between 444 and 473 nm, typical of a BOPHY-like vibronic progression. The racemic isomers were resolved by chiral HPLC and display mirror image ECD spectra. The absorption dissymmetry factor (|gabs|) for the tert-butyl catechol chelate is 5–10 fold larger than that for the ester-substituted catechol derivative, which correlates with a highly twisted core chromophore revealed by the X-ray crystal structure of the tert-butyl derivative. Both catechol chelates display BOPHY-like emission but with very low quantum yield of fluorescence (φf ≤ 0.1%) presumably due to photoelectron transfer from the very electron-rich catechol system.

Formation and fluorescent mechanism of red emissive carbon dots from o-phenylenediamine and catechol system

Carbon dots (CDs) as the advancing fluorescent carbon nanomaterial have superior potential and prospective. However, the ambiguous photoluminescence (PL) mechanism and intricate structure-function relationship become the greatest hindrances in the development and applications of CDs. Herein, red emissive CDs were synthesized in high yield from o-phenylenediamine (oPD) and catechol (CAT). The PL mechanism of the CDs is considered as the molecular state fluorophores because 5,14-dihydroquinoxalino[2,3-b] phenazine (DHQP) is separated and exhibits the same PL properties and behavior as the CDs. These include the peak position and shape of the PL emission and PL excitation and the emission dependence on pH and solvent polarity. Both of them display close PL lifetime decays. Based on these, we deduce that DHQP is the fluorophore of the red emissive CDs and the PL mechanism of CDs is similar to DHQP. During the PL emission of CDs, the electron of the molecule state can transfer to CDs. The formation process of DHQP is further confirmed by the reaction intermediates (phthalazine, dimers) and oPD. These findings provide insights into the PL mechanism of this type of CDs and may guide the further development of tunable CDs for tailored properties.

Noncovalent interactions in catechol/ammonium-rich adhesive motifs: Reassessing the role of cation-π complexes?

Cation-π interactions between ammonium and catechol groups provide a commonly held paradigm in the complex interplay of noncovalent forces that govern both biological phenomena, such as underwater adhesion in mussel byssus and other marine organisms, and aggregation processes in self-assembly of catecholamine-derived polymers. However, closer consideration of the peculiar properties of the catechol functionality, that features two adjacent phenoxyl groups endowed with chelating properties, would suggest operation of alternate interaction geometries besides typical cation-π. Following previous studies on various alkali metal cations, we report herein compelling computational evidence in favor of a so far overlooked σ-type interaction between the ammonium cation and the catechol system, as the most important contributor to binding, far exceeding the cation-π component. The present findings would hence prompt an experimental and theoretical reassessment of the actual importance of cation-π against σ-type interaction between ammonium and catechol groups in underwater adhesive patterns. In this framework, the catechol-ammonium interaction energy potential surfaces herein reported may provide an improved reference to approach more realistic natural and synthetic adhesion models encompassing other participating molecules/ions and the role of the solvent.

Rapid fabrication of xylan-based hydrogel by graft polymerization via a dynamic lignin-Fe3+ plant catechol system

Traditional preparation methods of the hydrogel are not only tedious but also requiring external stimuli. Here, a plant catechol-inspired self-catalytic system (sulfonated lignin and iron ion) has been introduced to rapidly trigger the graft polymerization of vinyl monomers on the carboxymethyl xylan (CMX) at room temperature, generating an elastic, UV-shield, and conductive hydrogel. The rapid preparation process can be finished at room temperature in 5 min without the removal of oxygen. The hydrogel shows charming extension ratio (up to 460%) and tensile stress (up to 23 kPa), which can be ascribed to the double network structure constructed from Fe3+ and CMX. The hydrogel exhibits great transparency (up to 85.37%), fascinating UV-blocking (up to 99%), and conductive features, thereby serving as potential human body sensors. The rapid preparation of xylan-derived hydrogels via dynamic lignin catechol chemistry may open up a new approach to high-valued utilization of biomass.

Flavonoid Preparations from Taraxacum officinale L. Fruits-A Phytochemical, Antioxidant and Hemostasis Studies.

Dandelion (Taraxacum officinale L.) roots, leaves, and flowers have a long history of use in traditional medicine. Compared to the above organs, dandelion fruits are the least known and used. Hence, the present paper was aimed at the phytochemical analysis of T. officinale fruit extract and estimating its antiradical, antiplatelet, and antioxidant properties related to hemostasis. Methanolic extract of fruits (E1), enriched with polyphenols (188 mg gallic acid equivalents (GAE)/g), was successfully separated into cinnamic acids (E2; 448 mg GAE/g) and flavonoids (E3; 377 mg GAE/g) extracts. Flavonoid extract was further divided into four fractions characterized by individual content: A (luteolin fraction; 880 mg GAE/g), B (philonotisflavone fraction; 516 mg GAE/g), C (flavonolignans fraction; 384 mg GAE/g), and D (flavone aglycones fraction; 632 mg GAE/g). High DPPH radical scavenging activity was evaluated for fractions A and B (A > B > Trolox), medium for extracts (Trolox > E3 > E2 > E1), and low for fractions C and D. No simple correlation between polyphenol content and antiradical activity was observed, indicating a significant influence of qualitative factor, including higher anti-oxidative effect of flavonoids with B-ring catechol system compared to hydroxycinnamic acids. No cytotoxic effect on platelets was observed for any dandelion preparation tested. In experiments on plasma and platelets, using several different parameters (lipid peroxidation, protein carbonylation, oxidation of thiols, and platelet adhesion), the highest antioxidant and antiplatelet potential was demonstrated by three fruit preparations–hydroxycinnamic acids extract (E2), flavonoid extract (E3), and luteolin fraction (A). The results of this paper provide new information on dandelion metabolites, as well as their biological potential and possible use concerning cardiovascular diseases.

Inhibition of hexose oxidase on the dark spots in fresh wet noodle sheets: A feasible prevention of dark spots

Hexose oxidase was a feasible prevention for the dark spots in the fresh wet noodle sheets (FWNS). The chemical mechanism that hexose oxidase recucing the melanins of dark spots was discussed basis on the UPLC-TOF-MS analysis of the polyphenol oxidase (PPO)-catechol system. In the process of PPO browning, hexose oxidase catalyzed the oxidation of o-benzoquinone derivatives and their oligomers, hindering the formation of melanins. Hexose oxidase was efficient in FWNS with low ash content when water addition was 24%~44% or pH range was 4 ~ 7.5. Hexose oxidase could inhubit dark spots in the presence of 10 metal ions. The recommended addition amount was 40 ~ 60 ppm, by which the dark spots could be compolitely inhibited. Hexose oxidase was also suitable for wholewheat and oat FWNS, ΔL6d of wholewheat and oat FWNS were reduced by 4 and 7.98, respectively.

Electrochemical Sensor under Nanostructured Materials

In order to study the electrochemical sensor of nanometer mechanism materials to realize the high sensitive detection of different chemical molecules, in this research, the preparation methods of molybdenum dioxide nanomaterials, molybdenum dioxide/metal particles (Au, Pt, Au@Pt) composites and the preparation of molybdenum dioxide nanomaterials, molybdenum dioxide /Au composite nanomaterials, molybdenum dioxide /Pt composite nanomaterials and molybdenum dioxide /Au @Pt composite nanomaterials were introduced. Then the electrochemical behavior of several modified electrodes, electrochemical behavior in catechol system, scanning and pH were applied to the modified electrode. Finally, the electrode p-catechol system was detected by differential pulse voltammetry and the actual samples were analyzed. The results showed that compared with unmodified electrode materials, the electrode modified by molybdenum dioxide nanomaterials, molybdenum dioxide /Au composite nanomaterials, molybdenum dioxide /Pt composite nanomaterials and molybdenum dioxide /Au @Pt composite nanomaterials has better electrocatalytic performance and the detection of catechol has a good effect. Among them, the electrochemical sensor constructed by MoS2-Au@Pt composite has the best detection performance for catechol. The results have a good guiding significance for the performance improvement of electrochemical sensor.

(-)-Tarchonanthuslactone: Design of New Analogues, Evaluation of their Antiproliferative Activity on Cancer Cell Lines, and Preliminary Mechanistic Studies.

Natural products containing the α,β-unsaturated δ-lactone skeleton have been shown to possess a variety of biological activities. The natural product (-)-tarchonanthuslactone (1) possessing this privileged scaffold is a popular synthetic target, but its biological activity remains underexplored. Herein, the total syntheses of dihydropyran-2-ones modeled on the structure of 1 were undertaken. These compounds were obtained in overall yields of 17-21 % based on the Keck asymmetric allylation reaction and were evaluated in vitro against eight different cultured human tumor cell lines. We further conducted initial investigation into the mechanism of action of selected analogues. Dihydropyran-2-one 8 [(S,E)-(6-oxo-3,6-dihydro-2H-pyran-2-yl)methyl 3-(3,4-dihydroxyphenyl)acrylate], a simplified analogue of (-)-tarchonanthuslactone (1) bearing an additional electrophilic site and a catechol system, was the most cytotoxic and selective compound against six of the eight cancer cell lines analyzed, including the pancreatic cancer cell line. Preliminary studies on the mechanism of action of compound 8 on pancreatic cancer demonstrated that apoptotic cell death takes place mediated by an increase in the level of reactive oxygen species. It appears as though compound 8, possessing two Michael acceptors and a catechol system, may be a promising scaffold for the selective killing of cancer cells, and thus, it deserves further investigation to determine its potential for cancer therapy.

Heterogeneous Fenton oxidation of catechol and 4-chlorocatechol catalyzed by nano-Fe3O4: Role of the interface

The nano-Fe3O4 catalyzed Fenton oxidations of catechol and 4-chlorocatechol in aqueous solution were comparably investigated to elucidate the interface reaction mechanism of the heterogeneous Fenton reactions. Nano-Fe3O4 were synthesized as quasi-spherical particles with specific surface areas of 57.84 m2/g. Almost all the catechol or 4-chlorocatechol was oxidized within 3 h after the addition of H2O2, while about only 10% of the parent compounds adsorbed onto nano-Fe3O4 without H2O2. And the oxidation curves followed the pseudo-second order kinetic model. 4-Chlorocatechol was oxidized faster than catechol, but with only 40% of mineralization. The contribution of homogeneous reaction induced by the leaching iron was limited. The surface generated reactive oxygen species were OH and HO2/O2-, which were further reacted to generate oxygen-centered radicals in both systems, and carbon-centered radicals only in catechol system. In-situ flow-cell ATR-FTIR spectroscopy further confirmed that the adsorbed catechol or 4-chlorocatechol remained on the nano-Fe3O4 surface, indicating an Eley–Rideal mechanism. Meanwhile, the generated carboxyl acids and some intermediates like ethers or dimers were also adsorbed. Accordingly, schematic diagrams of oxidation mechanisms of catechol and 4-chlorocatechol in nano-Fe3O4/H2O2 system were proposed.

Theoretical study of the Pb(II)–catechol system in dilute aqueous solution: Complex structure and metal coordination sphere determination

We investigated the unknown interaction of Pb(II) with catechol ligand in diluted aqueous solution by electronic spectroscopies combined with quantum chemical calculations. The aim of this work is the determination of the complete structure of the complex formed and particularly the metal coordination sphere. Three successive steps have been necessary to reach this goal: (i) the comparison of the experimental electronic absorption spectrum with theoretical spectra calculated from various hypothetical structures, (ii) complexation reaction pathways calculations in vacuum and with taking into account the solvent effects and finally (iii) the fluorescence emission wavelength calculations. All these investigations led to identify a monodentate complex with the monodeprotonated ligand, in which the Pb atom presents a coordination number of five. The formula of the complex is [ Pb ( Hcat ) ( H 2 O ) 4 ] mono + .

New aspects of biosynthesis and metabolism of N-acyldopamines in rat tissues

Possible biosynthetic pathways of N-acyldopamines in rat tissues were compared. It was shown that an insignificant amount of the conjugation products was formed during the incubation of arachidonic acid and dopamine, whereas the substitution of tyrosine for dopamine resulted in the productive biosynthesis of N-arachidonoyldopamine. The biosynthesis presumably involves several closely conjugated enzymatic stages, and free fatty acids rather than their CoA esters served as the starting substrates. The decarboxylation stage probably precedes the stage of catechol system formation, because N-acetyltyramine (a probable intermediate) was easily oxidized by monophenol monooxygenase to N-acyldopamine, whereas N-acyltyrosine is hydrolyzed under these conditions. Biosynthesis of N-acyldopamines in a cell-free medium was accompanied by their methylation. The possibility of oxidative metabolism of N-acyldopamines, which could serve as co-substrates or inhibitors of different oxidoreductases, was shown for the first time.

A novel and efficient route to the construction of the 4-oxa-tricyclo[4.3.1.0]decan-2-one scaffold

A short and efficient route to the synthesis of 4-oxa-tricyclo[4.3.1.0]decan-2-one scaffold 12 in good yield is reported. Essential to the synthesis was the implementation of selective protection of the catechol system in xanthone 2 with Ph 2CCl 2 and MOM groups. Subsequently, a biomimetic tandem Claisen/Diels–Alder reaction occurred to produce the desired tricyclic scaffold 11a as a single isomer. A rationalization of the excellent region and stereoselectivity of this transformation was also proposed.

Quantum Chemical Study of Photoinjection Processes in Dye-Sensitized TiO2 Nanoparticles

Results from quantum chemical INDO/S-CI calculations of the absorption properties of anatase TiO2 nanoparticles sensitized by catechol and benzoic acid are reported. Experimental observations that catechol causes a strong shift in the TiO2 absorption threshold, while benzoic acid does not, are explained from the calculations which indicate that only catechol introduces electronic levels in the TiO2 band gap. The 420 nm excitation in the TiO2 + catechol system responsible for the shift is seen to be a charge-transfer excitation from the catechol π HOMO orbital to Ti(3d) levels at the bottom of the conduction band. A direct photoinjection scheme which does not involve excited states of the adsorbate is proposed to account for the electron injection process.

Iron(III)-Chelating Properties of the Novel Catechol O-Methyltransferase Inhibitor Entacapone in Aqueous Solution

The iron(III) complex formation of entacapone, a novel catechol O-methyltransferase (CoMT) inhibitor, has been studied at 25°C in aqueous 0.1mol/L NaCl solution by using the electromotive force titration method. Entacapone functions as a bidentate ligand chelating through the catecholate oxygen atoms and forms stable iron(III) complexes with the formation constant of a tris complex: log ß-613 ([FeL33־][H]6+/ [Fe3+][H2L]3)=-6.9±0.1. Distribution curves show that entacapone is highly effective for iron (III) in moderately dilute solution (10—3 mol/L) whereas in very dilute solution (10-6 mol/L) the iron hydroxo complexes together with FeL33— dominate under physiological pH7.4. Comparison of iron (III) species distribution in a competitive two-ligand entacapone- catechol system reveals that the complexation of entacapone is favored at high and low dilution.

Influence of External Ligands and Auxiliaries on the Reactivity of Low-Valent Titanium in McMurry Reaction: Selectivity and Mechanistic Profile

Influence of various external ligands/auxiliaries on the reductive carbonyl coupling reactions mediated by low-valent titanium (LVT) reagents (McMurry coupling) has been explored. The LVT species generated from Tyrlik's TiCl3−Mg−THF system has been selected for the reactivity-tuning trials. Our studies show that incorporation of about 10 equiv of pyridine (a π-acceptor ligand) with respect to TiCl3 to the THF solvated LVT reagent could arrest the reductive dimerization of acetophenone at the intermediate pinacol stage. Modulation of the LVT-species by covalently-binding monohydroxy, 1,2- and 1,3-dihydroxy auxiliaries also resisted deoxygenation completely to give the pinacols in higher yields and better diastereoselectivity, as compared to pyridine-modified LVT system. Amongst these modified reagents, the LVT−catechol (1:1) system was found to be the most efficient combination for total pinacolization of aromatic carbonyl compounds, even under refluxing conditions. The actual titanium reagent responsible for this transformation is proposed to be a Ti(II) complex formed in situ. Further enhancement of stereoselectivity (threo-selectivity) of the pinacols has been achieved by carrying out the reactions with LVT-complexes modified by a variety of covalently-linking auxiliaries at low temperatures. The results demonstrate that by the judicious incorporation of various ligands/auxiliaries into LVT reagents it is possible to widen the scope and applicability of the classical McMurry reaction.

Multinuclear magnetic resonance studies on aluminium chelates. Part i. Chelates with catechol and disodium 4,5-dihydroxybenzene-1,3-disulfonate

The complexation of Al3+ with catechol and tiron (disodium 4,5-dihydroxybenzene-1,3-disulfonate) has been studied by NMR spectroscopy. The complexes in solution at different pH values were identified by multinuclear (27Al, 13C and 1H) magnetic resonance spectra, and spectrophotometric and potentiometric data. Aluminium formed 1:1, 1:2 and 1:3 chelates with both catechol and tiron depending on the pH and ligand concentration. Disproportionation of the 1:1 chelate with tiron at pH 7 gave a mixture of 1:2 and 1:3 chelates leaving a major amount of aluminium in an uncomplexed form. Both meridional and facial isomers of [AIL3]9–(Na2H2L = tiron) have been characterised by 13C and 1H NMR. Hydrolysis of the 1:1 Al–L4 chelate leading to the formation of [Al(OH)4] occurs via the formation of the tetrahedral chelate [AIL(OH)2]3–(δ 53) as an intermediate. In the Al–catechol (H2cat) system three complex species coexist with [Al(OH)4] in a 1:2 mixture at pH 12.5. Unlike in the Al–tiron system, a tetrahedral 1:2 Al–cat chelate (δ 58.5) is also formed during hydrolysis of the octahedral 1:2 Al–cat complex.

Equilibrium and Structural Studies of Silicon(IV) and Aluminium(III) in Aqueous Solution. 28. Formation of Soluble Silicic Acid--Ligand Complexes as Studied by Potentiometric and Solubility Measurements.

Amorphous silica solubilities in the presence of organic (mannitol, oxalate, citrate, catechol) and inorganic (SO 4 2− ) ligands have been studied in 0.6 M Na(Cl) medium at 25 o C. Apart from the catechol system, the experiments were performed at neutral pH with an equivalent ligand concentration of ≤0.6 M. In the presence of mannitol, the solubility of SiO 2 (am) was found to decrease with increasing ligand concentration. With oxalate, citrate and sulphate, an increased solubility was observed

Charge Transfer Complexes of Indole:Catechol Type II

Charge transfer complexes between tryptamine: epinephrine, tryptamine: isoproterenol, tryptamine: catechol, and indole: catechol were demonstrated spectrophotometrically in aqueous solutions containing 0.1M HCI. It was possible to make precise measurements and to calculate thermodynamic parameters and molar absorptivities. In general, the equilibrium constant was found to be quite low and ranged from 4.00 ± 0.04 to 0.30 ± 0.02M−1 These interactions are exothermic and have relatively large standard enthalpy and entropy changes (ΔH° values ranged from −7.4 ± 0.3 to −5.2 ± 0.4kcal mol−1; ΔS° ranged from −25 ± 5.0 to −16 ± 1.3cal K−1 mol−1). The similarity in ΔH° and ΔS° values for all the combinations indicates a similar interacting system. This result has led us to propose the involvement of the charge transfer effect, induced in the indole: catechol system, in the mechanism occurring in nerve conductions.

Model compounds for microbial iron-transport compounds. Part IV. Further solution chemistry and Mössbauer studies on iron(II) and iron(III) catechol complexes

Mössbauer spectroscopy and solution studies, together with Evans' Method to measure magnetic moments, on the complexes in the Iron(II)/Iron(III) catechol system are reported. A mechanism previously proposed for the reduction of Iron(III) to Iron(II) is modified by consideration of new evidence for the monoprotonation of the monocatecholato acid stable iron complex. The monoprotonated catechol moiety is the electron donor to the coordinated iron(III) and thus protonation of iron-containing hexadentate catecholate siderophores is probably essential for the reduction.