Ozlem Sahin

Synthesis of Chiral Calix[4]arene Derivative and Evaluation of its Recognition Properties

The article describes the synthesis and extraction properties of a new chiral calix[4]arene Schiff base ligand 5, which has been synthesized from 5,17-diformyl-25,27-bis-(4-nitrobenzyloxy)-26,28-dihidroxycalix[4]arene (4) by treatment with (S)-(-)-1-phenylethylamine. In this synthesis, it was thought to explore the role of chiral, as well as Schiff base sites in the recognition of targeted species ions (such as dichromate anions) as well as neutral/chiral molecules. At low pH, the ligand 5 is more effective for transferring the dichromate anions from an aqueous into a dichloromethane layer; may be due to the protonation of nitrogen atoms. The extraction properties of ligand 5 towards the some selected α -amino acid methylesters are also reported. However, the ligand 5 did not display any selectivity towards the selected α-amino acid methylesters.

Enantioselective hydrolysis of (R,S)-Naproxen methyl ester using Candida rugosa lipase with calix[4]arene derivatives

Candida rugosa lipase has been immobilized on a variety of calix[4]arene derivatives using the sol–gel encapsulation technique, and the catalytic activities of the resulting encapsulated lipases towards the hydrolysis of p-nitrophenyl palmitate and the hydrolytic kinetic resolution of racemic Naproxen methyl ester were evaluated using standard techniques. The results revealed that the calix[4]arene-based immobilized encapsulated lipases 5-CRL and 6-CRL gave higher levels of enantioselectivity and conversion than the free encapsulated lipase.

Chiral Calix[4]arenes-Bearing Prolinamide Functionality as Organocatalyst for Asymmetric Direct Aldol Reactions in Water

ABSTRACT The chiral calix[4]arene derivative (6) bearing an L-prolinamido group has been designed and proved to be a water compatible efficient organocatalysts for a direct enantioselective aldol reaction. Compound 6 catalyzes the aldol reaction of cyclohexanone and a variety of aromatic aldehydes yielding anti-aldol products in high yield with enantioselectivities of up to 93% and diastereoselectivity of up to 95:5.

An ethanol electrooxidation study on carbon-supported Pt-Ru nanoparticles for direct ethanol fuel cells

ABSTRACT Carbon supported Pt-Ru catalysts were prepared at varying Pt:Ru ratios by polyol method. The crystallite sizes of these catalysts were determined by X-ray diffraction technique. The specific surface areas of these catalysts were also defined by Brunauer–Emmett–Teller technique. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements were conducted on these carbon supported Pt-Ru catalysts to investigate the effect of ruthenium on the ethanol electrooxidation kinetics. Results indicated that Pt-Ru (25:1) catalyst showed the best ethanol electrooxidation activity. In conclusion, ethanol electrooxidation mechanism was proposed.

Bis-Schiff Base Derivatives of 2,5-Dihydroxybenzaldehyde: Synthesis, Characterization and Antimicrobial Activity of Their Cu(II), Co(II) and Zn(II) Complexes

In this study, three Schiff base ligands (N,N′-Bis(2,5-dihydroxybenzylidene)-4,4′- diaminodiphenylmethane (DHDPM), N,N′-Bis(2,5-dihydroxybenzylidene)- 1,2- diaminoethane (DHSalen) and N,N′-Bis(2,5-dihydroxybenzylidene)- 1,3-phenylenedimethanamine (DHSalomphen)) and their metal complexes were synthesized and characterized by infrared spectroscopy (IR), thermogravimetric analysis (TGA), nuclear magnetic resonance (1H NMR), fluorescence spectra, elemental analysis and magnetic susceptibility apparatuses. The antibacterial activity was also studied against Staphylococcus aureusATCC 29213, Streptococcus mutansRSHM 676, Enterococcus faecalisATCC 29212, Lactobacillus acidophilus RSHM 06029, Escherichia coli ATCC 25922 and Pseudomonas aeruginosaATCC 27853.

Composition dependent activity of PdAgNi alloy catalysts for formic acid electrooxidation

In the present study, the carbon supported Pd, PdAg and PdAgNi (Pd/C, PdAg/C and PdAgNi/C) electrocatalysts are prepared via NaBH4 reduction method at varying molar atomic ratio for formic acid electrooxidation. These as-prepared electrocatalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma mass spectrometry (ICP-MS), N2 adsorption-desorption, and X-ray electron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and lineer sweep voltammetry (LSV). While Pd50Ag50/C exhibits the highest catalytic activity among the bimetallic electrocatalyst, it is observed that Pd70Ag20Ni10/C electrocatalysts have the best performance among the all electrocatalysts. Its maximum current density is about 1.92 times higher than that of Pd/C (0.675 mA cm-2). Also, electrochemical impedance spectroscopy (EIS), chronoamperometry (CA) and lineer sweep voltammetry (LSV) results are in a good agreement with CV results in terms of stability and electrocatalytic activity of Pd50Ag50/C and Pd70Ag20Ni10/C. The Pd70Ag20Ni10/C catalyst is believed to be a promising anode catalyst for the direct formic acid fuel cell.

Synthesis and Dichromate Anion Extraction Ability of Calix[4]arene Schiff Base Derivatives

This study reports the synthesis and complexation properties of five new Schiff base derivatives of calix[4]arene (4–8), which have been synthesized from the condensation of bis(3-aminopropoxy)calix[4]arene with respective aldehyde (2-pyrrolecarbaldehyde, 2-thiophenecarboxaldehyde, furfural, 1-methylpyrrol-2-carboxaldehyde, or biphenyl-4-carboxaldehyde). In this synthesis, the role of a different binding site of calix[4]arene in the extraction of dichromate anions has been observed. The complexation properties of the new Schiff base derivatives of calix[4]arene toward HCr2O7 −/Cr2O7 − ions were studied by liquid–liquid extraction experiment. The results showed that the receptor 8 is more effective than other compound (4–7) for the removal of dichromate anion. The protonated Schiff base forms of the receptors were effective for transferring the HCr2O7 − anion from aqueous phase to a dichloromethane phase.

Methanol Electrooxidation Study on Mesoporous Silica Supported Pt–Co Direct Methanol Fuel Cell Anode

Abstract At present, Pt was impregnated by incipient wetness impregnation method on Co-doped SBA-15 catalysts prepared by sol-gel method at different weight percentages of Co to investigate the effect of Pt:Co ratio on methanol electrooxidation reaction (MOR). Cyclic voltammetry (CV), chronoamperometry (CA), and linear sweep voltammetry (LSV) techniques were employed to examine the MOR activities, poisoning capacity, and stability of these Pt/SBA-15 and Pt–Co/SBA-15 catalysts. Co presence in the platinum structure enhances the electrocatalytic activity of MOR, due to oxidation of Co at relatively low positive potentials. CV and CA measurements indicated that the most active catalyst was Pt–Co (86:14)/SBA-15 catalyst for MOR. Stability and poisoning measurements revealed that Co presence in the catalyst increases CO poisoning resistance and its stability, in agreement with CV and CA measurements.