In this work we report the synthesis and characterization of a set of 3-hydroxy-4-pyridinone copp... more In this work we report the synthesis and characterization of a set of 3-hydroxy-4-pyridinone copper(ii) complexes with variable lipophilicity. EPR spectroscopy was used to characterize the structure of copper(ii) complexes in solution, and as a tool to gain insight into solvent interactions. EPR spectra of solutions of the [CuL2] complexes recorded in different solvents reveal the presence of two copper species whose ratio depends on the nature of the solvent. Investigation of EPR spectra in the pure solvents methanol, dimethylsulfoxide, dichloromethane and their 50% (v/v) mixtures with toluene allowed the characterization of two types of copper signals (gzz = 2.30 and gzz = 2.26) whose spin-Hamiltonian parameters are consistent with solvated and non-solvated square-planar copper(ii) complexes. Regarding the potential biological application of ligands and complexes and to get insight into the partition properties in water-membrane interfaces, EPR spectra were also obtained in water-saturated octanol, an aqueous solution buffered at pH = 7.4 and liposome suspensions, for three compounds representative of different hydro-lipophilic balances. Analysis of the EPR spectra obtained in liposomes allowed establishment of the location of the complexes in the water and lipid phases. In view of the results of this work we put forward the use of EPR spectroscopy to assess the affinity of copper(ii) complexes for a hydrophobic environment and also to obtain indirect information about the lipophilicity of the ligands and similar EPR silent complexes.
ABSTRACT A previously reported fluorescein-based dye containing a catechol unit showed high sensi... more ABSTRACT A previously reported fluorescein-based dye containing a catechol unit showed high sensitivity to Fe(III) at physiological pH, but also undesirable pH sensitivity, mainly due to the lower pK(a) values of the phenolic hydroxyl groups of the fluorescein core. Aiming to synthesize compounds that interact with metal ions at physiological pH, exhibiting no pH sensitivity, we designed two novel fluorescent compounds by assembling, through amide linkage, a rhodamine fluorophore with two selected chelating moieties, catechol and 3-hydroxy-4-pyridinone, both possessing high affinity for Fe(III) but distinct pK(a) values. The fluorescent compounds were prepared using straightforward synthetic protocols and characterized by NMR, mass spectrometry and electronic spectroscopy (UV-Vis and fluorescence) and one of the compounds was also characterized by single crystal X-ray diffraction. The results reveal that, while the fluorescent 3-hydroxy-4-pyridinone derivative exhibits a significant dependence of fluorescence emission with increasing pH, due to the pK(a) values arising from the 3-hydroxy-4-pyridinone residue, the fluorescent catechol ligand responds mainly to interactions with metal ions, preferentially to Fe(III), showing less sensitivity to pH than the related ligands over the pH range 3-8, fact that is relevant concerning the application of this compound as an ion sensor in biological media.
Three new mononuclear oxovanadium(iv) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)im... more Three new mononuclear oxovanadium(iv) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)imino}acenaphthene, R = H, ; CH3, ; Cl, ) were prepared and characterized. They promoted the catalytic oxidation of olefins such as cyclohexene, cis-cyclooctene, and styrene with both tbhp (tert-butylhydroperoxide) and H2O2, and of enantiopure olefins (S(-)- and R(+)-pinene, and S(-)- and R(+)-limonene) selectively to their epoxides, with tbhp as the oxidant. The TOFs for styrene epoxidation promoted by complex with H2O2 (290 mol mol(-1)V h(-1)) and for cis-cyclooctene epoxidation by with tbhp (248 mol mol(-1)V h(-1)) are particularly good. Conversions reached 90% for several systems with tbhp, and were lower with H2O2. A preference for the internal C[double bond, length as m-dash]C bond, rather than the terminal one, was found for limonene. Kinetic data indicate an associative process as the first step of the reaction and complex [VO(acac)(H-BIAN)](+) ((+)) was isolated in an FTICR cell after adding tbhp to . EPR studies provide evidence for the presence of a V(iv) species in solution, until at least 48 hours after the addition of tbhp and cis-cyclooctene, and cyclic voltammetry studies revealed an oxidation potential above 1 V for complex . DFT calculations suggest that a [VO(H-BIAN)(MeOO)](+) complex is the likely active V(iv) species in the catalytic cycle from which two competitive mechanisms for the reaction proceed, an outer sphere path with an external attack of the olefin at the coordinated peroxide, and an inner sphere mechanism starting with a complex with the olefin coordinated to vanadium.
In this work we report the synthesis and characterization of a set of 3-hydroxy-4-pyridinone copp... more In this work we report the synthesis and characterization of a set of 3-hydroxy-4-pyridinone copper(ii) complexes with variable lipophilicity. EPR spectroscopy was used to characterize the structure of copper(ii) complexes in solution, and as a tool to gain insight into solvent interactions. EPR spectra of solutions of the [CuL2] complexes recorded in different solvents reveal the presence of two copper species whose ratio depends on the nature of the solvent. Investigation of EPR spectra in the pure solvents methanol, dimethylsulfoxide, dichloromethane and their 50% (v/v) mixtures with toluene allowed the characterization of two types of copper signals (gzz = 2.30 and gzz = 2.26) whose spin-Hamiltonian parameters are consistent with solvated and non-solvated square-planar copper(ii) complexes. Regarding the potential biological application of ligands and complexes and to get insight into the partition properties in water-membrane interfaces, EPR spectra were also obtained in water-saturated octanol, an aqueous solution buffered at pH = 7.4 and liposome suspensions, for three compounds representative of different hydro-lipophilic balances. Analysis of the EPR spectra obtained in liposomes allowed establishment of the location of the complexes in the water and lipid phases. In view of the results of this work we put forward the use of EPR spectroscopy to assess the affinity of copper(ii) complexes for a hydrophobic environment and also to obtain indirect information about the lipophilicity of the ligands and similar EPR silent complexes.
In this work we report the synthesis and characterization of a set of 3-hydroxy-4-pyridinone copp... more In this work we report the synthesis and characterization of a set of 3-hydroxy-4-pyridinone copper(ii) complexes with variable lipophilicity. EPR spectroscopy was used to characterize the structure of copper(ii) complexes in solution, and as a tool to gain insight into solvent interactions. EPR spectra of solutions of the [CuL2] complexes recorded in different solvents reveal the presence of two copper species whose ratio depends on the nature of the solvent. Investigation of EPR spectra in the pure solvents methanol, dimethylsulfoxide, dichloromethane and their 50% (v/v) mixtures with toluene allowed the characterization of two types of copper signals (gzz = 2.30 and gzz = 2.26) whose spin-Hamiltonian parameters are consistent with solvated and non-solvated square-planar copper(ii) complexes. Regarding the potential biological application of ligands and complexes and to get insight into the partition properties in water-membrane interfaces, EPR spectra were also obtained in water-saturated octanol, an aqueous solution buffered at pH = 7.4 and liposome suspensions, for three compounds representative of different hydro-lipophilic balances. Analysis of the EPR spectra obtained in liposomes allowed establishment of the location of the complexes in the water and lipid phases. In view of the results of this work we put forward the use of EPR spectroscopy to assess the affinity of copper(ii) complexes for a hydrophobic environment and also to obtain indirect information about the lipophilicity of the ligands and similar EPR silent complexes.
ABSTRACT A previously reported fluorescein-based dye containing a catechol unit showed high sensi... more ABSTRACT A previously reported fluorescein-based dye containing a catechol unit showed high sensitivity to Fe(III) at physiological pH, but also undesirable pH sensitivity, mainly due to the lower pK(a) values of the phenolic hydroxyl groups of the fluorescein core. Aiming to synthesize compounds that interact with metal ions at physiological pH, exhibiting no pH sensitivity, we designed two novel fluorescent compounds by assembling, through amide linkage, a rhodamine fluorophore with two selected chelating moieties, catechol and 3-hydroxy-4-pyridinone, both possessing high affinity for Fe(III) but distinct pK(a) values. The fluorescent compounds were prepared using straightforward synthetic protocols and characterized by NMR, mass spectrometry and electronic spectroscopy (UV-Vis and fluorescence) and one of the compounds was also characterized by single crystal X-ray diffraction. The results reveal that, while the fluorescent 3-hydroxy-4-pyridinone derivative exhibits a significant dependence of fluorescence emission with increasing pH, due to the pK(a) values arising from the 3-hydroxy-4-pyridinone residue, the fluorescent catechol ligand responds mainly to interactions with metal ions, preferentially to Fe(III), showing less sensitivity to pH than the related ligands over the pH range 3-8, fact that is relevant concerning the application of this compound as an ion sensor in biological media.
Three new mononuclear oxovanadium(iv) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)im... more Three new mononuclear oxovanadium(iv) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)imino}acenaphthene, R = H, ; CH3, ; Cl, ) were prepared and characterized. They promoted the catalytic oxidation of olefins such as cyclohexene, cis-cyclooctene, and styrene with both tbhp (tert-butylhydroperoxide) and H2O2, and of enantiopure olefins (S(-)- and R(+)-pinene, and S(-)- and R(+)-limonene) selectively to their epoxides, with tbhp as the oxidant. The TOFs for styrene epoxidation promoted by complex with H2O2 (290 mol mol(-1)V h(-1)) and for cis-cyclooctene epoxidation by with tbhp (248 mol mol(-1)V h(-1)) are particularly good. Conversions reached 90% for several systems with tbhp, and were lower with H2O2. A preference for the internal C[double bond, length as m-dash]C bond, rather than the terminal one, was found for limonene. Kinetic data indicate an associative process as the first step of the reaction and complex [VO(acac)(H-BIAN)](+) ((+)) was isolated in an FTICR cell after adding tbhp to . EPR studies provide evidence for the presence of a V(iv) species in solution, until at least 48 hours after the addition of tbhp and cis-cyclooctene, and cyclic voltammetry studies revealed an oxidation potential above 1 V for complex . DFT calculations suggest that a [VO(H-BIAN)(MeOO)](+) complex is the likely active V(iv) species in the catalytic cycle from which two competitive mechanisms for the reaction proceed, an outer sphere path with an external attack of the olefin at the coordinated peroxide, and an inner sphere mechanism starting with a complex with the olefin coordinated to vanadium.
In this work we report the synthesis and characterization of a set of 3-hydroxy-4-pyridinone copp... more In this work we report the synthesis and characterization of a set of 3-hydroxy-4-pyridinone copper(ii) complexes with variable lipophilicity. EPR spectroscopy was used to characterize the structure of copper(ii) complexes in solution, and as a tool to gain insight into solvent interactions. EPR spectra of solutions of the [CuL2] complexes recorded in different solvents reveal the presence of two copper species whose ratio depends on the nature of the solvent. Investigation of EPR spectra in the pure solvents methanol, dimethylsulfoxide, dichloromethane and their 50% (v/v) mixtures with toluene allowed the characterization of two types of copper signals (gzz = 2.30 and gzz = 2.26) whose spin-Hamiltonian parameters are consistent with solvated and non-solvated square-planar copper(ii) complexes. Regarding the potential biological application of ligands and complexes and to get insight into the partition properties in water-membrane interfaces, EPR spectra were also obtained in water-saturated octanol, an aqueous solution buffered at pH = 7.4 and liposome suspensions, for three compounds representative of different hydro-lipophilic balances. Analysis of the EPR spectra obtained in liposomes allowed establishment of the location of the complexes in the water and lipid phases. In view of the results of this work we put forward the use of EPR spectroscopy to assess the affinity of copper(ii) complexes for a hydrophobic environment and also to obtain indirect information about the lipophilicity of the ligands and similar EPR silent complexes.
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