Experimental and theoretical studies on isatin-Schiff bases and their copper(II)-complexes: Syntheses, spectroscopy, tautomerism, redox potentials, EPR, PXRD and DFT/TDDFT

Palladium(0) Catalyzed Synthesis of (E)-4-Bromo-N-((3-bromothiophen-2-yl)methylene)-2-methylaniline Derivatives via Suzuki Cross-Coupling Reaction: An Exploration of Their Non-Linear Optical Properties, Reactivity and Structural Features

A series of (E)-4-bromo-N-((3-bromothiophen-2-yl)methylene)-2-methylaniline analogs synthesized in considerable yields through Suzuki cross-coupling reactions. Various electron donating and withdrawing functional moieties were successfully incorporated under the employed reaction conditions. Reaction of 4-bromo-2-methylaniline (1) with 3-bromothiophene-2-carbaldehyde (2b) in the existence of glacial acetic acid, provided (E)-4-bromo-N-((3-bromothiophen-2-yl)methylene)-2-methylaniline (3b) in excellent yield (94%). Suzuki coupling of 3b with different boronic acids in the presence of Pd(PPh₃)₄/K₃PO₄ at 90 °C led to the synthesis of the monosubstituted and bisubstituted products 5a-5d and 6a-6d in moderate yields (33-40% and 31-46%, respectively). Density functional theory (DFT) investigations were performed on different synthesized analogues 5a-5d, 6a-6d to determine their structural characteristics. The calculations provide insight into the frontier molecular orbitals (FMOs) of the imine-based analogues and their molecular electrostatic potential (MESP). Reactivity descriptors like ionization energy (I), electron affinity (A), chemical hardness (ƞ) and index of nucleophilicity have been calculated for the first time for the synthesized molecules.

Pseudotetrahedral copper(II)-complexes with enantiopure (R or S)-2-(((aryl)ethylimino)ethyl)phenolate Schiff base ligands

Condensation of 2-hydroxy-benzophenone (HL') with (R or S)-(Ar)ethylamine yields the enantiopure Schiff bases (S or R)-2-((E)-1-(1-(Ar)ethylimino)ethyl)phenol {Ar = C6H5 (S- or R-HL1), p-CH3OC6H4 (S- or R-HL2)}. These Schiff bases react with copper(ii) acetate under reflux to give green microcrystals of bis[(R or S)-2-((E)-1-(1-(Ar)ethylimino)ethyl)phenolato-κ2N,O]-Λ/Δ-copper(ii), {Ar = C6H5 (Λ/Δ-Cu-R- or S-L1), p-CH3OC6H4 (Λ/Δ-Cu-R- or S-L2)} with induction of Λ/Δ-chirality at-metal. The presence of Schiff base ligands in the paramagnetic green microcrystals is confirmed by decomplexation reaction with NaCN via reduction of Cu(ii) to Cu(i) in DMSO-d6 solution. Crystallization attempts of the green microcrystalline Schiff-base Cu complexes provide deep-green block-shaped crystals of an about equal admixture of bis[2-oxo-benzophenonato-κ2O,O']-copper(ii), (CuL'2) and bis[2-(imino(phenyl)methyl)phenolato-κ2N,O]copper(ii), (CuL''2) via in situ hydrolysis of the coordinated Schiff base ligands back to 2-hydroxy-benzophenone (HL') and to 2-(imino(phenyl)methyl)phenol (HL''), which in-turn bind with the copper(ii) ion. Powder X-ray diffraction (PXRD) patterns of R-HL1 and Cu-R-L1 allowed their structure determinations using the program Expo-2014 followed by Rietveld refinement. The Cu structures refined to four-coordinated Λ/Δ-copper(ii)-complexes by the two phenolate-oxygen and two imine-nitrogen atoms from two Schiff base ligands in a pseudotetrahedral geometry. DFT optimized structures (at gas-phase) reveal the Δ-Cu-S-L1 or Λ-Cu-R-L1 diastereomer as slightly more stable than the corresponding Λ-Cu-S-L1 or Δ-Cu-R-L1 by ca. 7.60 kcal mol-1, resulting from diastereoselectively induced Λ vs. Δ-chirality at-metal. Electronic circular dichroism (ECD) spectra display mirror-image relationships and comparisons of experimental and simulated ECD spectra by TDDFT suggest an excess of the Δ-Cu-S-L1 or Λ-Cu-R-L1 diastereomer in solution. The cyclic voltammograms demonstrate two one electron charge transfer processes for Cu2+/Cu+ and Cu+/Cu0 couples in acetonitrile, respectively.

A novel nano copper complex: potentiometry, DFT and application as a cancer prostatic biomarker for the ultrasensitive detection of human PSA

A novel analytical approach for cancer prostatic biomarker by PSA detection using nano-Cu(II)-complex.