Co-Schiff Base Research Articles

Co-Schiff base complexes functionalized on graphene as efficient heterogeneous nanocatalysts for alcohols oxidation

Different Schiff base complexes were prepared by immobilizing three aldehydes (4-Hydroxybenzaldehyde, 2-hydroxybenzaldehyde, and 2-Pyridinecarboxaldehyde) on graphene oxide and were fully characterized using multiple techniques such as FTIR, XRD, TGA, BET, SEM-EDS, and TEM. Then efficient heterogeneous catalysts were checked out in the selective catalytic oxidation of benzylic alcohols. The effects of different parameters, such as reaction time and temperature, were examined to obtain optimum reaction conditions. The solvent-free oxidation reaction of benzylic alcohols showed a conversion above 70% and selectivity higher than 95% in the presence of cobalt (II) Schiff base catalysts using H2O2 as an oxidant after 40 min of reaction. The reusability experiment results specified that the prepared catalysts could maintain high catalytic activity in the oxidation of benzylic alcohols (>80%) and selectivity (>96%) even after being used for three cycles.

Preparation of co-schiff base complex and its adsorption desulfurization

Twelve schiff base metal complexes were synthesized, and selected to adsorption desulfurization of dibenzothiophene(DBT). The result showed that the schiff base metal complex of melamine and cobalt (SF-S/Co) was the optimal adsorbent. Then SF-S/Co was characterized by scanning electron microscopy(SEM), Brunner − Emmet − Teller(BET) measurements, fourier transform infrared spectroscopy(FTIR), X-ray diffraction, and energy spectroscopy analysis. The effects of adsorbent amount and adsorption time on adsorption desulfurization were studied. The optimal adsorption condition was 1.5 g adsorbent/100 mL model oil, and the adsorption time was 8 min at room temperature. Under the optimal condition, the adsorption removal rate of DBT is up to 95%. The maximum adsorption capacity of the adsorbent for DBT is 21.66 mg/g. The adsorption capacity of adsorbent didn’t decreased obviously after being reused for 5 times. The adsorption isothermal model and dynamics of the adsorption process was further studied. The results show that the adsorption process of DBT by this adsorbent followed the Freundlich adsorption isothermal model and the pseudo-second-order model kinetics. The absorption effect of this adsorbent on different sulfides also was investigated. The order of removal efficiency was: dibenzothiophene > benzothiophene > thiophene.

Synthesis and Characterization of Cobalt(II) and Manganese(II) Schiff Base Complexes: Metal Effect on the Binding Affinity with β-Casein

In this study, two metal Schiff base complexes (cobalt(II) and manganese(II), were synthesized and characterized by 1H-NMR and FT-IR analyses. The in vitro binding behavior of this complexes with β-Casein (β-CN) was investigated by using biophysical techniques. For evaluation the thermodynamics parameters of interaction between Schiff base complexes and β-CN,the fluorescence data at different temperatures were done. The results showed that the intrinsic fluorescence of the β-CN was quenched by increasing the complexes through the dynamic quenching mechanism. Also, these complexes demonstrated a considrable binding affinity to β-CN and the process is mainly entropy driven. Fluorescence resonance energy transfer was used in order to estimating the distance between donor (β-CN) and acceptor (complex). Results demonstrated that the sequence of tendency of the complexes to β-CN was as follows: Mn-Schiff base complex > Co-Schiff base complex. All these experimental results propose that β-CN might act as carrier protein for Co(II) and Mn (II) complexes to deliver it to the target molecules.

Deactivation of Co-Schiff base catalysts in the oxidation of para-substituted lignin models for the production of benzoquinones

Those features which enhance the reactivity of Co-Schiff base oxidation catalysts can also contribute to their demise.

MCM-41@Schiff base-Co(OAc)2 as an efficient catalyst for the synthesis of pyran derivatives

Heterogeneous ordered mesoporous silica materials catalyst, MCM-41@Schiff base-Co(AcO)2, reveals high catalytic performance within the synthesis of pyran derivatives using the multicomponent reaction of aldehydes, malononitrile and 2-naphthol (or cyclohexane-1,3-dione) in water. The reactions afforded the desired products in high yields (up to 97% and 95%). The substantial feature is that the mesoporous-complex catalyst could be easily separated from the reaction mixture by centrifugation and reused at least 6 times with more than 80% yield in activity. The gram-scale experiments were achieved with good yields and implied that the catalytic method was effective and convenient for heterocyclic synthesis. What is more, the synthesized catalyst was characterized using various spectroscopic techniques to obtain the structural and functional features. The analysis results confirmed that the Co-Schiff base complex immobilized on the surface of mesoporous materials MCM-41. Finally, a plausible reaction mechanism was proposed.

Al2O3 based Co-Schiff Base complex catalyst in hydrogen generation

This work presents the study of the catalytic activity of aluminum oxide supported Co-Schiff Base complex derived from 4,4′-Methylenebis(2,6-diethylaniline)-3,5-ditertbutylsalicylaldimine-Co-Schiff Base complex in sodium borohydride hydrolysis. This catalyst is characterized with XRD, FT-IR, SEM, TEM, and BET. The respective reaction kinetics have been calculated. With the catalyst condition, maximum reaction (initial) rate is 106540 and 147193,3 mL H2/gcat..min. at 30 °C and 50 °C. For this reaction apparent activation energy is 44,7792 kJ.mol−1 with 20–50 °C. The reaction order value (n) for this catalytic system is 0,31. Additionally when Al2O3 supported Co-Schiff Base complex compared with pure Co-Schiff Base complex, the experimental results show that the aluminum oxide support exhibits enhancing effect with 106540 and 64147 mL H2/gcat. min respectively in sodium borohydride hydrolysis to Hydrogen production.

Synthesis of Novel Schiff Base Cobalt (II) and Iron (III) Complexes as Cathode Catalysts for Microbial Fuel Cell Applications

In this study, the synthesis and characterization of a new Schiff base and its cobalt(II) and iron(III) complexes were performed fully characterized by common spectroscopic techniques such as 1H-NMR, 13C-NMR, FT-IR, UV–Vis and MS and elemental analysis. The cathodes prepared with only activated carbon, Co-Schiff base complex, and Fe-Schiff base complex mixed with activated carbon as the carrier were examined in single chamber air cathode microbial fuel cells (MFCs). The spectroscopic results confirm the structure of novel Schiff base and its complexes with cobalt (II) and Fe(III). MFC results showed that Fe-Schiff base complex generated higher voltage generation using glucose as the carbon source. Cyclic voltammetry results showed the conductivity and catalytic features of the cathodes developed in this study. Scanning electron microscopic results showed the distribution the complexes on the cathode surface. In conclusion, a novel Schiff base and its complexes with cobalt (II) and iron (III) can be employed into MFC technology to be used in green electricity production, and might help decreasing the operating costs of wastewater treatment plants.

Steric effects of bulky tethered arylpiperazines on the reactivity of Co-Schiff base oxidation catalysts—a synthetic and computational study

New C2-symmetric and C2-asymmetric Co-Schiff base catalysts tethered to arylpiperazine units were synthesized and used to oxidize phenolic lignin models to para-benzoquinones. Synthetic approaches to these catalysts were optimized to include fewer steps and broaden the types of catalyst structures available. In contrast to conventional Co-Schiff base catalysts, these systems induce phenolic oxidation in the absence of an external axial base, simplifying the process. Asymmetric catalysts bearing a phenylethylene or diphenylmethyl piperazine substituent display the highest catalytic activity observed to date for the conversion of S-models to 2,6-dimethoxybenzoquinone (DMBQ). Computational analysis shows that more reactive catalysts populate conformations that favor oxidation in preference to non-productive decomposition routes. This balance between catalyst reactivity and catalyst deactivation is optimized by inclusion of sufficient steric bulk around the periphery of the Schiff base ligand, reducing catalyst deactivation and allowing oxidations to proceed in the absence of an added axial ligand.

Metal-Schiff Base complex catalyst in KBH4 hydrolysis reaction for hydrogen production

It is the first study to synthesize Co(II)-Schiff Base complex and to use it like a catalyst for potassium borohydride hydrolysis reaction to hydrogen production. Co(II)-complex is synthesized with CoCl2·6H2O and 5-Amino-2,4-dichlorophenol-3,5-di-tert-butylsalisylaldimine ligand. KBH4 hydrolysis reaction is studied according as percentage of KBH4, percentage of KOH, amount of Co-Schiff Base complex catalyst and temperature effects. Co-Schiff Base complex is highly effective catalyst and initial rates (Ro) of KBH4 hydrolysis reaction were 61220.00 and 99746.67 mL H2. g−1 cat. min−1 at 30 °C and 50 °C. Furthermore this study includes the kinetic calculations and for this reaction calculated activation energy is 17.56 kJ mol−1.

Synthesis and characterization of redox non-innocent cobalt(III) complexes of a O,N,O donor ligand: Radical generation, semi-conductivity, antibacterial and anticancer activities

Structural, spectroscopic, electrochemical, electrical conductivity and biological characterizations of cobalt-HBAP [2-(2-hydroxybenzylideneamino) phenol] complexes has been reported. This tridentate HBAP ligand forms a slightly distorted bis octahedral complex, [CoIII(O∩N∩O)2](NEt3H)(H2O)2 (1)−. Several solution state spectroscopic measurements e.g.; UV–Vis, Cyclic voltammetry, EPR, NMR, ESI-MS along with solid state characterizations e.g.; CHN, FT-IR and Single Crystal XRD are performed to authenticate the formation of the ligand as well as its Co-metallated complexes. 1e− oxidation of (1)− to (1)0 have shown an intense phenoxyl radical based transition in UV–Vis spectra. Electron paramagnetic resonance of (1)0 identifies the presence of phenoxyl radical. Meanwhile similar attempt in generation of 1e− reduced species (1)2− provides metal based reduction having metal hyperfines coming from Co nuclear spin I=7/2. Interestingly, the low spin diamagnetic mononuclear Co(III)-Schiff base complex forms a supramolecular saw teeth like 1D network via hydrogen bonding interaction in presence of countercation [NEt3H]+ and solvent water molecules which are present in the system as solvent of crystallization. Fascinatingly, semiconducting property is found in both ligand and its cobalt metallated complexes. Current–voltage (I–V) and alternating current (AC) studies are carried out to show their effectiveness as functional material. Ligand and Complex (1)− exhibited their effective anti-cancer and anti-bacterial activities. Density functional theoretical (DFT) calculations have shown redox noninnocence of Co-Schiff base complexes is in accord with the experimental outcomes.

Understanding the Transcriptional and Translational Regulatory Roles of Non-Classical Neural Zinc Finger Proteins Involved in the Development of the Nervous System

Zinc plays a crucial role in the development of the nervous system. Disruption of zinc homeostasis results in several nervous system disorders, including cerebral stroke, Alzheimer's disease, schizophrenia, mental retardation, periventricular leukomalacia, and brain cancer. Two ‘zinc finger’ proteins, Neural Zinc Finger Factor-1 (NZF-1) and Myelin Transcription Factor 1 (MyT1), play key roles in the development of the nervous system: NZF-1 regulates the development of neurons and MyT1 regulates the development of oligodendrocytes. Both proteins contain clusters of highly homologous yet modular CCHHC domains that can selectively recognize/regulate different genes when zinc is coordinated to the domains. The mechanisms of zinc mediated DNA recognition by these proteins is not well understood. Using a combination of biochemical, biophysical and spectroscopic approaches, including fluorescence anisotropy, NMR spectroscopy and mass spectrometry, we have begun to map out the key interactions that drive molecular recognition and we will present a current model for these recognition events. In addition, we will present evidence that a novel Co-Schiff base complex inhibits the function of NZF-1, by disrupting the zinc coordination and accompanying folding of the CCHHC domains. This complex has the potential to be used as a functional probe and small molecule inhibitor of NZF-1.

Synthesis, crystal structures, electrochemically studies and antibacterial properties of three new mono-nuclear and one very rare bi-nuclear cobalt(III) Schiff base complexes

Three new mononuclear and one new binuclear cobalt(III) complexes of tetradentate N2O2 donor Schiff base ligands [CoIII(L1)(3-Mepy)2]PF6 (1), [CoIII(L2)(3-Mepy)2]PF6 (2), [CoIII(L2)(4-Mepy)2]PF6 (3) and [CoIII2(L1)2(4-Mepy)4(PF6)4(K)2] (4) were synthesized by reaction of the resp. tetradentate ligands (L1=bis(acetylacetone)ethylenediimine dianion, L2=bis(benzoylacetone)ethylenediimine dianion) with the corresponding cobalt(II) salts in the presence of 3-Mepy and 4-Mepy. These complexes were characterized by FT-IR, 1H NMR and UV–Vis spectroscopy. The crystal structures of the complexes were determined by X-ray crystallography on solvated crystals. In dimeric cobalt(III) complex, two Co-Schiff base units were connected to two K(+) and four PF6 molecules to form the centrosymmetric, dimeric bi-nuclear complex, in which the Co(3+) cations showed distorted octahedral coordinations, while K(+) cations had different coordination numbers in two symmetry-independent moieties: in one of them it is 9-coordinated (irregular tricapped trigonal prism) and in the other 8-coordinated (distorted square prism). Biological activities of the complexes were studied on Staphylococcus aureus, Salmonella typhi, Escherichia coli, and Bacillus subtilis by the well diffusion method. The electrochemical behavior of these complexes with the goal of evaluating the structural effects on the redox properties was also studied.

Catalytic Performance of Cobalt-Schiff Base-Chitosan/attapulgite for Epoxidation of Styrene

With the Schiff base of L-aspartic acid and salicylaldehyde as the ligands,the composite resin of chitosan/attapulgite(CS/ATP) produced by NaOH curing method as the carrier,the Schiff base metal complexes and the load-type Schiff base metal complexes of Co,Mn,Cu,Fe,Ni were synthesized.Their structural characterizations were determined by FT-IR.The catalytic performance of each catalyst for epoxidation of styrene was studied.Experiments show that the catalytic performance of Co-Schiff base is better in small molecule ligand Schiff base metal complexes.Therefore,Co-Schiff base was loaded in CS/ATP composite resin and the effects of the amount of Co-Schiff base-CS/ATP catalyst,reaction temperature and reaction time on the catalytic epoxidation of styrene were investigated.Finally the results show that the best reaction conditions are as follows:the temperature is 80 ℃ and the reaction time is 8 h,which results in a conversion rate of 93.1% for epoxidation of styrene.

Steric effects in the design of Co-Schiff base complexes for the catalytic oxidation of lignin models to para-benzoquinones

New Co-Schiff base complexes that incorporate a sterically hindered ligand and an intramolecular bulky piperazine base in close proximity to the Co center are synthesized. Their utility as catalysts for the oxidation of para-substituted lignin model phenols with molecular oxygen is examined. Syringyl and guaiacyl alcohol, as models of S and G units in lignin, are oxidized in good yield using a catalyst bearing an N-benzylpiperazinyl substituent, with the catalysts displaying improved reactivity for G oxidation. Computational evaluation of the catalysts shows that the piperazinyl substituent is within bonding distance of the Co center. The increased steric interference is suggested as the source of increased G reactivity.

Efficient Cobalt-Catalyzed Oxidative Conversion of Lignin Models to Benzoquinones

Phenolic lignin model monomers and dimers representing the primary substructural units of lignin were successfully oxidized to benzoquinones in high yield with molecular oxygen using new Co-Schiff base catalysts bearing a bulky heterocyclic nitrogen base as a substituent. This is the first example of a catalytic system able to convert both S and G lignin model phenols in high yield, a process necessary for effective use of lignin as a chemical feedstock.

An efficient catalyst Co(salophen) for synthesis of diethyl carbonate by oxidative carbonylation of ethanol

The oxidative carbonylation of ethanol to diethyl carbonate (DEC) was investigated by an efficient catalyst system comprising of Co-Schiff base complexes. Effects of Schiff base ligands, reaction time, catalyst concentration, temperature and pressure on the catalytic activity were studied. Co(salophen) [N,N′-bis(salicylidene) o-phenylenediamine cobalt] catalyst exhibited better catalytic activity compared with other Co complexes. When the oxidative carbonylation was carried out at the reaction conditions: 0.12mol/L Co(salophen), P(CO)/P(O2)=2:1, 3.0MPa, 140°C, 2.5h, the conversion of ethanol is 15.8%, the selectivity to DEC is 99.5% and the turnover number (TON) is 22.2. The corrosion behavior of Co(salophen) catalyst to the stainless steel reactor was also examined. The corrosion rate to the stainless steel by Co(salophen) catalyst is below 0.005mm/a. SEM images demonstrated that the pitting corrosion was not observed on the surface of the stainless steel.

Cobalt-Schiff Base Complex Catalyzed Oxidation of Para-Substituted Phenolics. Preparation of Benzoquinones

Para-substituted phenolics, serving as models for lignin (a renewable source of carbon), are oxidized to the corresponding benzoquinone with oxygen in the presence of catalytic amounts of Co-Schiff base complexes. The reaction products observed depend on the structure of the catalyst. The 5-coordinate catalysts (pyridine)[bis(salicylidene)ethylenediamine]cobalt[(pyr)Co(salen)]and[bis(salicylideneamino)ethylamine]cobalt [Co(n-Me salpr)] convert syringyl alcohol (3,5-dimethoxy-4-hydroxybenzyl alcohol) to 2,6-dimethoxybenzoquinone in high yield. In contrast, syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde) is unreactive toward these catalysts. However, the 4-coordinate Co(salen) converts syringaldehyde to 2,6-dimethoxybenzoiquinone in 72% isolated yield. Phenols bearing a single methoxy group on the ring are unreactive toward any catalyst in MeOH. However, vanillyl alcohol (3-methoxy-4-hydroxybenzyl alcohol) is converted to 2-methoxybenzo-quinone with Co(N-Me salpr) and oxygen in 43% yield in CH{sub 2}Cl{sub 2} and 58% yield in CH{sub 2}Cl{sub 2} in the presence of 1% CuCl{sub 2}. The success of the oxidations appears to be related to the ease of removal of the phenolic hydrogen by the Co/O{sub 2} complex. Competitive deactivation of the catalyst occurs with substrates of lower reactivity. 84 tabs.