Some Aromatic Schiff Bases and Their Metal Complexes

Schiff bases represent a widely studied group of compounds, interesting from the synthetic and structural, but also applicational point of view. Among these, aromatic Schiff bases stand out due to their stability and possible application as safer therapeutic agents. Since the presence of the phenolic group and the heteroatom in the benzene ring seems to be of interest for the biological activity of Schiff bases, imine derivatives of some dihydroxybenzaldehydes, 2-acetylpyridine, and 2,6-diacetylpyridine are chosen to be described here. The syntheses, structural features, as well as investigations of possible application of Schiff bases themselves, but also their metal complexes are described. The Cambridge Structural Database has been searched to obtain a better knowledge of the structures of these Schiff bases and their metal complexes, structural changes upon coordination, and the most common and interesting modes of coordination. The main accent is given to those compounds that are promising candidates for medicinal and pharmaceutical use, but some of the described complexes are good as catalysts, optical materials, sensors, analytical reagents, etc

Synthesis and structural characterization of Cd(II) complexes with 2-acetylpyridine-aminoguanidine - a novel coordination mode

The structures of the first two complexes with bidentate coordination of aminoguanidine Schiff base, i.e., 2-acetylpyridine-aminoguanidine (L), are reported. The complex of the formula [Cd2Cl6(HL)2] (1) was obtained in the reaction of warm aqueous solutions of chloride salts of Cd(II), Zn(II) and the ligand, while the reaction of cadmium bromide and the ligand in the presence of deprotonating agent as well as ammonium thiocyanate resulted in the formation of the complex in which Schiff base has both the role of the ligand and the counterion, viz., [HL][Cd(HL)(NCS)2XY]·H2O (2), where X is Cl- or Br-, and Y Br- or SCN-. The complexes were characterized by IR spectroscopy, elemental analysis, conductometric measurements and single crystal X-ray diffraction. The unusual bidentate coordination of the Schiff base lead to significant changes in the geometry of this molecule (from almost planar in free form and as a tridentate ligand to twisted as a bidentate ligand). Besides, in complex 1 relatively rare bridging coordination of Cl- in octahedral Cd(II) is found, while the crystal structure of complex 2 exhibits substitutional disorder, and contains four different anions: [Cd(HL)(NCS)2Br(SCN)]- (ca. 61 %), [Cd(HL)(NCS)2Cl(SCN)]- (ca. 35 %), [Cd(HL)(NCS)2Br2]- (ca. 3 %) and [Cd(HL)(NCS)2ClBr]- (ca. 1 %)

First cobalt complexes with methyl pyruvate semi/thiosemicarbazone - synthesis, physico-chemical and structural characterization

In the reaction of acetone solutions of CoX2∙nH2O (X = Cl, Br) with methyl pyruvate semi/thiosemicarbazone (Hmps, Hmpt) the first Co(II) complexes with these ligands, i.e., [Co(Hmps)(H2O)X2] (X = Cl (1), Br (2)), [Co(Hmpt)2][CoCl4]∙2H2О (3) and [Co(Hmpt)2]Br2∙Me2CO (4) were obtained. Complexes 1 and 2 represent the first examples of metal complexes of Hmps. All the obtained compounds were characterized by elemental analysis, conductometry, magnetic measurements, and IR spectra, and for complexes 2–4, single crystal X-ray diffraction analysis was also performed. The effective magnetic moments were close to the upper limit (5 μB) for complexes 1 and 2, and close to the lower limit (4.4 μB) for complexes 3 and 4, and as such are characteristic for high-spin Co(II) complexes. Structural analysis showed that both ligands coordinate in a neutral form in a tridentate manner, via the ester oxygen, imine nitrogen and the oxygen atom of the ureido (Hmps), or the sulfur atom of the thioureido group (Hmpt). The central metal atoms are situated in a deformed octahedral coordination environment. Complex 2 has cis-Br configuration, while complexes 3 and 4 have mer-configuration

Supplementary data for the article: Mrđan, G. S.; Vastag, G. G.; Škorić, D. Đ.; Radanović, M. M.; Verbić, T. Ž.; Milčić, M. K.; Stojiljković, I. N.; Marković, O. S.; Matijević, B. M. Synthesis, Physicochemical Characterization, and TD–DFT Calculations of Monothiocarbohydrazone Derivatives. Structural Chemistry 2021, 32 (3), 1231–1245. https://doi.org/10.1007/s11224-020-01700-y.

Supplementary material for: [https://doi.org/10.1007/s11224-020-01700-y]Related to published version: [https://cherry.chem.bg.ac.rs/handle/123456789/4453

Syntheses and characterization of 2-acetylpyridine-aminoguanidine and its copper(II) complexes: Crystallographic and antimicrobial study

The syntheses, physico-chemical and microbiological properties of the ligand, 2-acetylpyridine-aminoguanidine dihydrogensulfate monohydrate and its five complexes with Cu(II) are described. The compounds were characterized by single crystal X-ray crystallography. Common fragments encountered in some of the structures were compared by r.m.s. overlay calculations as well as half-normal probability plots. In these complexes the chelate ligand is coordinated in its neutral form in a tridentate N-3-coordination mode, via pyridine, azomethine and imino nitrogen atoms of the aminoguanidine fragment. In these complexes the Cu(II) ion is situated in moderately or severely distorted square-pyramidal surroundings. The antimicrobial activity of the ligand and the complexes were examined against 6 selected bacterial and 3 fungal strains.This is peer-reviewed version of the following article: Vojinović-Ješić, L. S.; Radanović, M. M.; Rodić, M. V.; Živković-Radovanović, V.; Jovanović, L. S.; Leovac, V. M. Syntheses and Characterization of 2-Acetylpyridine-Aminoguanidine and Its Copper(II) Complexes: Crystallographic and Antimicrobial Study. Polyhedron 2016, 117, 526–534. [https://doi.org/10.1016/j.poly.2016.06.032]Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3583

2-Acetylpyrydine-aminoguanidine Schiff base – Novel ligand salt and zinc(II) complex containing thiocyanate

A new salt of Schiff base of aminoguanidine and 2-acetylpyridine, and its zinc(II) complex were obtained and their physicochemical and structural properties studied. The reaction of an aqueous solution of the chloride ligand salt and NH4NCS resulted in formation of the dithiocyanate ligand salt, L·2HNCS, while the reaction of the obtained salt with zinc(II) acetate gave a neutral complex of the formula [ZnL(NCS)2]. In this complex, chelate ligand is coordinated in its neutral form, in a common tridentate NNN manner, via pyridine, azomethine and imino nitrogen atoms of the aminoguanidine fragment. This coordination mode results in formation of two strained five-membered metallocycles. Zinc(II) is situated in a distorted square-pyramidal environment of the tridentate ligand and one thiocyanate ion in the equatorial and the other thiocyanate ion in the apical position. The crystal structure of the ligand salt is stabilized by N–H…N and N–H…S interactions formed between the cationic and anionic species, while the three-dimensional crystal packing of the complex units is based on weak N–H…S interactions which involve the S acceptors from both NCS ligands. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172014

Crystal structure of trans-diaqua-bis(methyl methylcarbamohydrazonothioato-κ2 N,N′) nickel(II) iodide semihydrate, C6H22N6O2NiS2I2·0.5H2O

C6H23I2N6NiO2.50S2, monoclinic, C2/c (no. 15), a = 8.2282(4) Å, b = 21.9200(7) Å, c = 11.4906(4) Å, β = 109.451(4)°, V = 1954.19(14) Å3, Z = 4, Rgt (F) = 0.0322, wRref (F 2) = 0.1113, T = 295

Computational Identification and Characterization of a Promiscuous T-Cell Epitope on the Extracellular Protein 85B of Mycobacterium spp. for Peptide-Based Subunit Vaccine Design

Tuberculosis (TB) is a reemerging disease that remains as a leading cause of morbidity and mortality in humans. To identify and characterize a T-cell epitope suitable for vaccine design, we have utilized the Vaxign server to assess all antigenic proteins of Mycobacterium spp. recorded to date in the Protegen database. We found that the extracellular protein 85B displayed the most robust antigenicity among the proteins identified. Computational tools for identifying T-cell epitopes predicted an epitope, 181-QQFIYAGSLSALLDP-195, that could bind to at least 13 major histocompatibility complexes, revealing the promiscuous nature of the epitope. Molecular docking simulation demonstrated that the epitope could bind to the binding groove of MHC II and MHC I molecules by several hydrogen bonds. Molecular docking analysis further revealed that the epitope had a distinctive binding pattern to all DRB1 and A and B series of MHC molecules and presented almost no polymorphism in its binding site. Moreover, using “Allele Frequency Database,” we checked the frequency of HLA alleles in the worldwide population and found a higher frequency of both class I and II HLA alleles in individuals living in TB-endemic regions. Our results indicate that the identified peptide might be a universal candidate to produce an efficient epitope-based vaccine for TB

Synthesis, Physicochemical, Thermal and Antioxidative Properties of Zn(II) Coordination Compounds with Pyrazole-Type Ligand

The reactions of pyrazole derivative, i.e., ethyl-5-amino-1-methyl-1H-pyrazole-4-carboxylate (L) with zinc halogenides in methanolic solution and zinc nitrate and zinc acetate in acetonic solution are described. The formulae of synthesized compounds are ZnL2Cl2 (1), [ZnL2Br2] (2), ZnL2I2·0.5MeOH (3), [Zn(L)2(H2O)4](NO3)2 (4), and {ZnL(OAc)2}2 (5). Two complexes are obtained in form of single crystals: [ZnL2Br2] (2) and [Zn(L)2(H2O)4](NO3)2 (4). Their crystal and molecular structure were determined by single-crystal X-ray structure analysis. The FTIR spectra of compounds prove the complex formation with all five zinc salts. The complexes are characterized by conductometric and thermoanalytical measurements, and their antioxidative activity was also tested by the scavenging effect on the DPPH radical. Conductometric results, solvolytic stability, and antioxidative activity of the compounds are in correlation

Synthesis, Physicochemical, Thermal and Antioxidative Properties of Zn(II) Coordination Compounds with Pyrazole-Type Ligand

The reactions of pyrazole derivative, i.e., ethyl-5-amino-1-methyl-1H-pyrazole-4-carboxylate (L) with zinc halogenides in methanolic solution and zinc nitrate and zinc acetate in acetonic solution are described. The formulae of synthesized compounds are ZnL2Cl2 (1), [ZnL2Br2] (2), ZnL2I2·0.5MeOH (3), [Zn(L)2(H2O)4](NO3)2 (4), and {ZnL(OAc)2}2 (5). Two complexes are obtained in form of single crystals: [ZnL2Br2] (2) and [Zn(L)2(H2O)4](NO3)2 (4). Their crystal and molecular structure were determined by single-crystal X-ray structure analysis. The FTIR spectra of compounds prove the complex formation with all five zinc salts. The complexes are characterized by conductometric and thermoanalytical measurements, and their antioxidative activity was also tested by the scavenging effect on the DPPH radical. Conductometric results, solvolytic stability, and antioxidative activity of the compounds are in correlation