Spectroscopic characterization and photophysical properties of schiff base metal complex

Zn (II) complex with vanillin derived Schiff base: antifungal, antibacterial, antioxidant and anticholinesterase activities

AIM

To synthesize and characterize a Schiff base derived from vanillin and tris(hydroxymethyl)aminomethane (VTRIS) and the Zinc (II) complex [Zn(VTRIS)2](CH3COO)2.

MATERIALS AND METHODS

VTRIS and the Zn (II) complex were synthesized through condensation and complexation reactions, respectively. Structures were confirmed by electron spectroscopy in the UV-Vis, FT-IR and NMR regions. Toxicity was evaluated in Artemia salina, antimicrobial activity was evaluated by microdilution assay, ABTS and DPPH methods were used for antioxidant effect and the anticholinesterase potential was investigated.

RESULTS

VTRIS and the complex showed low toxicity in Artemia salina (LC50 = 698.56 and 543.88, respectively). VTRIS did not show antifungal or antibacterial activity, but the complex showed MICs ranging from 32 to 128 μg/mL against Cryptococcus neoformans and Candida spp. and 512 μg/mL against Staphylococcus aureus, demonstrating an antimicrobial effect improvement after coordination to the metal center. VTRIS and the complex showed excellent results as antioxidant molecules, and the complex presented lower values than the standard quercetin in the ABTS method (IC50 = 1.08 and 1.63 μg/mL, respectively). VTRIS and the complex showed anticholinesterase potential of 1.93 and 1.83 μg/mL.

CONCLUSION

Zn complexation potentiates VTRIS, and this compound exhibits promising antimicrobial, antioxidant, and anticholinesterase activities at nontoxic concentrations.

Synthesis, Structural Characterization, Hirshfeld Surface Analysis, and Antibacterial Study of Pd(II) and Ni(II) Schiff Base Complexes Derived from Aliphatic Diamine

A Schiff base bearing two methyl substituents, namely, 6,6'-((1E,1'E)-((2,2-dimethylpropane-1,3-diyl) bis(azanylylidene)) bis(methanylylidene)) bis(2-methylphenol) [H₂AD1Me] was synthesized and characterized through physicochemical and spectroscopic analyses. Then, the Schiff base was complexed with Pd(II) and Ni(II) to form [Pd(AD1Me)] and [Ni(AD1Me)], respectively. Both metal complexes were successfully obtained and characterized through several analyses, viz., melting point, elemental analysis, molar conductivity, magnetic susceptibility, FTIR, ¹H NMR, UV-vis, and single crystal X-ray diffraction. A quantitative analysis of the intermolecular interactions in the crystal structures has been performed using Hirshfeld surface analysis. Both metal complexes were crystallized in a monoclinic crystal system with the space group of P2₁/c. Additionally, the deprotonated phenolic oxygen atom (O1/O2) and azomethine nitrogen atom (N1/N2) of the ligand chelate the Pd(II) and Ni(II) ions, forming a slightly distorted square-planar complex containing three six-membered rings encircling the metal core with dsp² hybridization. The shift of ν(C=N) to a higher frequency in FTIR by 26-28 cm^-1 indicated that the complexation to Pd(II) and Ni(II) through the azomethine N was established. It was further supported through the shifting of the azomethine proton signal to higher or lower chemical shifts with Δδ = 0.43-1.15 ppm in ¹H NMR. In addition, the shifting of the n-π*(C=N) band in UV-vis spectra with Δλ = 24-40 nm indicated the involvement of azomethine nitrogen in the complexation. All the compounds showed no significant antibacterial activity against three bacterial strains, namely, Staphylococcus aureus subsp. aureus Rosenbach (ATCC 6538), Streptococcus mutans Clarke (ATCC 700,610), and Proteus vulgaris (ATCC 6380), as the percent growth inhibition calculated was less than 90%.

Nickel (II) chloride schiff base complex: Synthesis, characterization, toxicity, antibacterial and leishmanicidal activity

The use of schiff base complex against microbial agentes a has recently received more attention as a strategy to combat infections caused by multidrug-resistant bacteria and leishmania. This study aimed to evaluate the toxicity, antibacterial and leishmanicidal activities of the nickel (II) chloride schiff base complex ([Ni(L2)] against Leishmania amazonensis promastigote, multi-resistant bacterial strains and evaluate to modulate antibiotic activity against multi-resistant bacterial. The schiff base complex was characterized by the techniques of elemental analysis, Fourier transform infrared spectroscopy (FTIR), UV-vis absorption spectroscopy and thermal analysis (TGA/DTG/DSC). The [Ni(L2)] complex presented moderate toxicity in saline artemia (LC₅₀ = 150.8 μg/mL). In leishmanicidal assay, the NiL2 complex showed values of IC₅₀ of (6.079 μg/mL ± 0.05656 at the 24 h), (0.854 μg/mL ± 0.02474, 48 h) and (1.076 μg/mL ± 0.04039, 72 h). In antibacterial assay, the [Ni(L2)] complex presented significant inhibited the bacterial growth of P. aeruginosa (MIC = 256 μg/mL). However, [Ni(L2)] complex did not present clinically relevant minimum inhibitory concentration (MIC ≥1024 μg/mL) against S. aureus and E. coli. The combination of [Ni(L2)] complex and antibacterial drugs resulted in the increased antibiotic activity of gentamicin and amikacin against S. aureus and E.coli multi-resistant strains. Thus, our results showed that [Ni(L2)] complex is a promising molecule for the development of new therapies associated with aminoglycoside antibiotics and in disease control related to resistant bacteria and leishmaniasis.

Multi-ion imprinted polymers (MIIPs) for simultaneous extraction and preconcentration of Sb(III), Te(IV), Pb(II) and Cd(II) ions from drinking water sources

Simultaneous extraction and preconcentration of several potentially toxic metal ions have received great attention because of their toxicological effects on aquatic life and human beings. Multi-ion imprinted polymers (MIIP) have proved to be promising adsorbents with excellent specific recognition performance than single-ion imprinted polymer. Therefore, in this study, the MIIP strategy was employed for simultaneous extraction and enrichment of Sb(III), Cd(II), Pb(II) and Te(IV) ions from drinking water sources. MIIPs was used as a sorbent material in ultrasound-assisted dispersive solid phase extraction combined with inductively coupled plasma optical emission spectrometry (UA-DSPE/ICP-OES). The experimental parameters that affect the extraction efficiency and recovery of Sb(III), Cd(II), Pb(II) and Te(IV) were investigated using response surface methodology. Under optimum conditions, the enhancement factors, linear range, limit of detection (LOD) and limit of quantification (LOQ) were 37.7-51.1, 0.04-100 µg L^-1, 0.011-0.28 µg L^-1, 0.037-093 µg L^-1, respectively. The intra-day (n = 10) and inter-day (n = 5) precision expressed as relative standard deviations (%RSDs,) were 3% and 5%, respectively. The proposed UA-DSPE/ICP-OES method was applied for preconcentration and determination of the trace metal ions in environmental samples. Furthermore, the accuracy of the method was evaluated using spiked recovery experiments and the percentage recoveries ranged from 95% to 99.3%.

Crystal, spectroscopic and quantum mechanics studies of Schiff bases derived from 4-nitrocinnamaldehyde

Two Schiff bases, (E)-1-(4-methoxyphenyl)-N-((E)-3-(4-nitrophenyl)allylidene)methanamine (compound 1) and (E)-N-((E)-3-(4-nitrophenyl)allylidene)-2-phenylethanamine (compound 2) have been synthesized and characterized using spectroscopic methods; time of flight MS, ¹H and ¹³C NMR, FT-IR, UV-VIS, photoluminescence and crystallographic methods. The structural and electronic properties of compounds 1 and 2 in the ground state were also examined using the DFT/B3LYP functional and 6-31 + G(d,p) basis set, while the electronic transitions for excited state calculations were carried out using the TD-DFT/6-31 + G(d,p) method. The Schiff base compounds, 1 and 2 crystallized in a monoclinic crystal system and the P2₁/c space group. The emission spectra of the compounds are attributed to conjugated π-bond interaction while the influence of the intra-ligand charge transfer resulted in a broad shoulder for 1 and a double emission peak for 2. The calculated transitions at 450 and 369 nm for 1 and 2 respectively are in reasonable agreement with the experimental results. The higher values of dipole moment, linear polarizability and first hyperpolarizability of 1, suggest a better optical property and better candidate for the development of nonlinear optical (NLO) materials.

In Vitro Cytotoxicity Studies on Human Thyroid Gland Undifferentiated Carcinoma Cells Using the Nickel Complex of (Z)-3-Bromo-5-((p-tolylimino)methyl)phenol

Metal complexes for medical applications are the promising area of research and metallo-drugs have been developed and evaluated to enhance the efficiency of drugs and minimize their side effects. This study describes the synthesis of a Schiff base ligand (Z)-3-bromo-5-((p-tolylimino)methyl)phenol from the reaction of 5-bromosalicilaldehyde and p-toluidine, and its subsequent complexation with nickel. Characterization and cell viability studies were performed for both Schiff base ligand and its metal complex with ¹H-NMR, FTIR, TG analysis, and UV-VIS spectrometry. With the aim of proving the Ni complex formation, quantitative analysis was done with flame atomic absorption spectrometry. The recovery result obtained for the formed complex was 103.9%. The cell viability of human thyroid gland undifferentiated carcinoma cells (8305C) treated with the Ni-ligand complex was determined as 12.7 ± 0.17%. It was observed that the nickel complex could be a significant anticancer agent as tested by the MTT assay method. Graphical Abstract .