Quinolines by Three-Component Reaction: Synthesis and Photophysical Studies

<div><p>The synthesis of five quinolines 8-octyloxy-4-[4-(octyloxy)phenyl]quinoline and 6-alkoxy- 2-(4-alkoxyphenyl)-4-[(4-octyloxy)aryl]quinolines are described by three-component coupling reaction mediated by Lewis acid FeCl3 and Yb(OTf)3. 4-n-octyloxybenzaldehyde, anisaldehyde, 4-n-octyloxyaniline p-anisidine, and 1-ethynyl-4-heptyloxybenzene, 1-ethynyl-4-octyloxybenzene and 2-ethynyl-6-heptyloxynaphthalene are the reagents in this protocol. A Yb3+ catalyst resulted in higher yields of quinolines than Fe3+. Polarizing optical microscopy (POM) revealed that none of the quinolines were liquid crystals, even the more anisotropic. UV-Vis measurements of one of the quinolines in polar solvent show two absorption bands at 280 and 350 nm related to π,π* and n,π* transitions. No changes were observed to lower-energy absorption band (ε < 104 mol L-1 cm-1) related to n,π* transition. A laser flash photolysis study for one of the quinolines relates a main transient band at 450 nm with a lifetime of 2.6 µs in ethanol, which is completely quenched in the presence of oxygen. This transient band was assigned to triplet-triplet absorption of one of the quinolines, which is semi-oxidised in the presence of phenol. Radiative rate constants have been determined along singlet and triplet excited state energies (3.39 and 3.10 eV, respectively). The chemical structure of one of the quinolines was also unequivocally confirmed by single-crystal X-ray analysis.</p></div

New La(III) Complex Immobilized on 3‑Aminopropyl-Functionalized Silica as an Efficient and Reusable Catalyst for Hydrolysis of Phosphate Ester Bonds

Described herein is the synthesis, structure, and monoesterase and diesterase activities of a new mononuclear [La^III(L¹)­(NO₃)₂] (<b>1</b>) complex (H₂L¹ = 2-bis­[{(2-pyridylmethyl)-aminomethyl}-6-[<i>N</i>-(2-pyridylmethyl) aminomethyl)])-4-methyl-6-formylphenol) in the hydrolysis of 2,4-bis­(dinitrophenyl)­phosphate (2,4-BDNPP). When covalently linked to 3-aminopropyl-functionalized silica, <b>1</b> undergoes disproportionation to form a dinuclear species (<b>APS-1</b>), whose catalytic efficiency is increased when compared to the homogeneous reaction due to second coordination sphere effects which increase the substrate to complex association constant. The anchored catalyst <b>APS-1</b> can be recovered and reused for subsequent hydrolysis reactions (five times) with only a slight loss in activity. In the presence of DNA, we suggest that <b>1</b> is also converted into the dinuclear active species as observed with <b>APS-1</b>, and both were shown to be efficient in DNA cleavage

Second-Coordination-Sphere Effects Increase the Catalytic Efficiency of an Extended Model for Fe^IIIM^II Purple Acid Phosphatases

Herein we describe the synthesis of a new heterodinuclear Fe^IIICu^II model complex for the active site of purple acid phosphatases and its binding to a polyamine chain, a model for the amino acid residues around the active site. The properties of these systems and their catalytic activity in the hydrolysis of bis­(2,4-dinitrophenyl)­phosphate are compared, and conclusions regarding the effects of the second coordination sphere are drawn. The positive effect of the polymeric chain on DNA hydrolysis is also described and discussed

Second-Coordination-Sphere Effects Increase the Catalytic Efficiency of an Extended Model for Fe^IIIM^II Purple Acid Phosphatases

Herein we describe the synthesis of a new heterodinuclear Fe^IIICu^II model complex for the active site of purple acid phosphatases and its binding to a polyamine chain, a model for the amino acid residues around the active site. The properties of these systems and their catalytic activity in the hydrolysis of bis­(2,4-dinitrophenyl)­phosphate are compared, and conclusions regarding the effects of the second coordination sphere are drawn. The positive effect of the polymeric chain on DNA hydrolysis is also described and discussed

Synthesis and Solvatochromism of Substituted 4‑(Nitrostyryl)phenolate Dyes

4-(Nitrostyryl)­phenols <b>2a</b>–<b>9a</b> were synthesized, and by deprotonation in solution, the solvatochromic phenolates <b>2b</b>–<b>9b</b> were formed. Their absorption bands in the vis region of the spectra are due to π–π* electronic transitions, of an intramolecular charge-transfer nature, from the electron-donor phenolate toward the electron-acceptor nitroarene moiety. The frontier molecular orbitals and natural bond orbitals were analyzed for the protonated and deprotonated forms. The calculated geometries are in agreement with X-ray structures observed for <b>4a</b>, <b>6a</b>, and <b>8a</b>. The HOMO–LUMO energy gaps suggest that, after their deprotonation, an increase in the electron delocalization is observed. In the protonated compounds, the HOMO is primarily localized over the phenol ring and the CC bridge. After deprotonation, it extends toward the entire molecule, including the NO₂ groups. The solvatochromism of each dye was studied in 28 organic solvents, and it was found that all compounds exhibit a reversal in solvatochromism, which is interpreted in terms of the ability of the media to stabilize their electronic ground and excited states to different extents. The Catalán multiparameter equation is used in the interpretation of the solvatochromic data, revealing that the most important contribution to the solute/solvent interaction is the hydrogen-bond donor acidity of the solvent

Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper­(II) complexes, using the unsymmetrical ligands <i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L1</b>) and <i>N</i>′,<i>N</i>′-bis­(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)­(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L2</b>). The structures of the complexes [Cu₂(<b>L1</b>)­(μ-OAc)]­(ClO₄)₂·(CH₃)₂CHOH (<b>1</b>) and [Cu₂(<b>L2</b>)­(μ-OAc)]­(ClO₄)·H₂O·(CH₃)₂CHOH (<b>2</b>) were determined by X-ray crystallography. The complex [Cu₂(<b>L3</b>)­(μ-OAc)]²⁺ [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807–1822). Magnetic data show that the Cu^II centers in <b>1</b> and <b>2</b> are antiferromagnetically coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = −4.3 cm^–1 for <b>1</b> and <i>J</i> = −40.0 cm^–1 for <b>2</b>) is a function of the Cu–O–Cu bridging angle. In addition, <b>1</b> and <b>2</b> were tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu^II-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis­(dinitrophenyl)­phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu^II center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (<i>K</i>_ass. and <i>k</i>_cat.) of <b>1</b> and <b>2</b> in comparison with that found for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity

Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper­(II) complexes, using the unsymmetrical ligands <i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L1</b>) and <i>N</i>′,<i>N</i>′-bis­(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)­(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L2</b>). The structures of the complexes [Cu₂(<b>L1</b>)­(μ-OAc)]­(ClO₄)₂·(CH₃)₂CHOH (<b>1</b>) and [Cu₂(<b>L2</b>)­(μ-OAc)]­(ClO₄)·H₂O·(CH₃)₂CHOH (<b>2</b>) were determined by X-ray crystallography. The complex [Cu₂(<b>L3</b>)­(μ-OAc)]²⁺ [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807–1822). Magnetic data show that the Cu^II centers in <b>1</b> and <b>2</b> are antiferromagnetically coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = −4.3 cm^–1 for <b>1</b> and <i>J</i> = −40.0 cm^–1 for <b>2</b>) is a function of the Cu–O–Cu bridging angle. In addition, <b>1</b> and <b>2</b> were tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu^II-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis­(dinitrophenyl)­phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu^II center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (<i>K</i>_ass. and <i>k</i>_cat.) of <b>1</b> and <b>2</b> in comparison with that found for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity

Synthesis, Magnetostructural Correlation, and Catalytic Promiscuity of Unsymmetric Dinuclear Copper(II) Complexes: Models for Catechol Oxidases and Hydrolases

Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper­(II) complexes, using the unsymmetrical ligands <i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-<i>N</i>-(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L1</b>) and <i>N</i>′,<i>N</i>′-bis­(2-pyridylmethyl)-<i>N</i>,<i>N</i>-(2-hydroxybenzyl)­(2-hydroxy-3,5-di-<i>tert</i>-butylbenzyl)-1,3-propanediamin-2-ol (<b>L2</b>). The structures of the complexes [Cu₂(<b>L1</b>)­(μ-OAc)]­(ClO₄)₂·(CH₃)₂CHOH (<b>1</b>) and [Cu₂(<b>L2</b>)­(μ-OAc)]­(ClO₄)·H₂O·(CH₃)₂CHOH (<b>2</b>) were determined by X-ray crystallography. The complex [Cu₂(<b>L3</b>)­(μ-OAc)]²⁺ [<b>3</b>; <b>L3</b> = <i>N</i>-(2-hydroxybenzyl)-<i>N</i>′,<i>N</i>′,<i>N</i>-tris­(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. <i>Inorg. Chim. Acta</i> <b>2005</b>, <i>358</i>, 1807–1822). Magnetic data show that the Cu^II centers in <b>1</b> and <b>2</b> are antiferromagnetically coupled and that the difference in the exchange coupling <i>J</i> found for these complexes (<i>J</i> = −4.3 cm^–1 for <b>1</b> and <i>J</i> = −40.0 cm^–1 for <b>2</b>) is a function of the Cu–O–Cu bridging angle. In addition, <b>1</b> and <b>2</b> were tested as catalysts in the oxidation of the model substrate 3,5-di-<i>tert</i>-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu^II-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis­(dinitrophenyl)­phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu^II center that contains the phenol group with <i>tert</i>-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (<i>K</i>_ass. and <i>k</i>_cat.) of <b>1</b> and <b>2</b> in comparison with that found for complex <b>3</b>. In fact, complexes <b>1</b> and <b>2</b> show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity