Schiff bases

Structures of the main resonance and tauto-meric forms of three Schiff bases of 2-hydroxy-1-naph-thaldehyde (1OXA), 5-bromosalicylaldehyde (2OXA) and 5-nitrosalicylaldehyde (3OXA) with 1,8-diamine-3,6-di-oxaoctane, before and after protonation and complexation of monovalent metal cations, have been studied by FTIR, 1 H, 13 C and 15 N NMR methods. The spectroscopic investigations provided clear evidence that the Schiff bases exist in acetonitrile solution as three different tautomers: 1OXA in enamine-oxo, 2OXA in imine-hydroxy and 3OXA in a low-barrier OÁÁÁHÁÁÁN imine-oxo forms. It was found on the basis of multinuclear NMR studies, that in solid state, the enamine-oxo and imine-hydroxy tautomers are formed exclusively, but not the untypical imine-oxo tautomer, which requires strong stabilisation by solvent molecules in solution. MOG-PM6 calculations of the different tautomers allowed visualisation of their energetically the most favourable structures. Protonation of 1OXA–3OXA Schiff bases leads to formation of common forms, i.e. protonated imine-hydroxy structure, irrespectively of the structure of tautomer before protonation. In turn, coordination of monovalent metal cations implies common formation of zwitterionic forms within all studied ligands in solution. Application of FT-IR and NMR titrations in combination with ESI MS spectrometry revealed the nature and the structure of OXA complexes, whose formation is impeded by the intra-and intermolecular interactions. MOG-PM6 calculations allowed visualisation of Li ? and Na ? metal coordination sphere geometries within structure of all investigated complexes, stabilised by intermolecular interactions with solvent molecules.

New push–pull (A–D) nickel(II) compounds of general formula [Ni(5-A-5’-D-saltn)] (3a–3l) with unsymmetrically-substituted N2O2 tetradentate Schiff base ligands are reported here. The ligands 5-A-5’-D-saltn2− (H2saltn = N,N’-bis(salicylidene)diaminopropane) possess differently-substituted salicylaldehyde (A/Dsal) moieties condensed to 1,3-diaminopropane (tn), and carry either an electron acceptor (A = H, Br, or NO2) or donor (D = H, Me, or OMe) group in the para position with respect to the coordinated phenoxido oxygen atoms. These compounds could be obtained by template synthesis involving derivatives [Ni(Gsal)2(H2O)2], 1a–e (G = NO2, Br, H, Me and OMe, respectively) and [Ni(GL)2], 2a–d (GL− = (E)-2-((3-aminopropylimino)methyl)-4-G-phenolate, G = NO2, Br, H and Me, respectively). Scrambling of the ligands and condensation to compounds 3 was suitably achieved by refluxing compounds 1 and 2 that carry the G groups suitable for the desired final A–D combination. Dinuclear intermediates [Ni2(μ-GL)2(G’sal)2] (4a,b,e,f,g) were also detected and isolated. The single-crystal X-ray diffraction structures of [Ni(5’-OMe-saltn)]·CHCl3 (3c·CHCl3), [Ni(5-Br-5’-OMe-saltn)]·EtOH (3g·EtOH) and [Ni(5-NO2-saltn)] (3j) show different degrees of distortion around the central core, leading to saddle-like (3c), planar (3g) and step-like (3j) molecular conformations. DFT geometrical optimization of the compounds showed that, for isolated molecules, the saddle-like conformation is slightly more stable with respect to the other conformations. UV-visible absorption spectra showed structured absorption profiles at about 320–440 nm, whose intensity was amplified by the presence of the nitro group, and this was assigned to a convolution of one metal-to-ligand charge transfer and two intra-ligand charge transfer transitions by TDDFT computations. Surprisingly, UV-visible spectra of the derivatives with Br were comparable to the derivatives with Me, suggesting that in this case the behaviour of the halogen was as a weak electron donor group. The experimental investigation (through electric-field-induced second-harmonic and solvatochromic measurements) of the second-order NLO responses of compounds 3, in conjunction with the theoretical calculations, revealed that the observed NLO efficiency is determined by the combined effect of two almost orthogonal charge transfer directions within the molecules, one along the axis approximately bisecting the donor and the accepting moieties and the
other along the A–D axis.

Schiff bases are an important class of organic compounds. The common structural feature of these compounds have the azomethine group with the general formula RHC = N-R1, where R and R1 are alkyl, aryl, cycloalkyl, or heterocyclic groups. Schiff bases have also been shown to exhibit a broad range of biological activities, including antifungal, antibacterial, antimalarial, antiproliferative, anti-inflammatory, antiviral, antipyretic properties and also have some industrial applications. The imine group present in such compounds has been shown to be critical to their biological activities

Schiff bases are synthesized by Sterker reaction in which condensation of primary aromatic amines with aryl aldehydes is found to be catalyzed by using mild catalysts in presence of organic solvent.

Owing to vast applications of Schiff bases in field of medicine, agriculture and industry; the work presented here was carried out to synthesize indole based Schiff bases. Different substituted anilines and novel-indolic aldehyde are used to synthesize various kinds of imines using green procedure that doesn’t require excess of organic solvents. This eco-friendly reaction has many advantages like economical, medicinal, environmental and with mild reaction conditions, simple work-up yield high products.

— Vanillin which is a naturally occurring food component found in plants is used for the manufacture of Schiff base chelates. The chelates and complexes find applications as anti mutagen, anticlastogen, DNA PK inhibitor, anticarcinogen, inhibitor of non-homogenous DNA end-joining (NHEJ) etc. They form complexes with a wide variety of metals including rare earths. They are incorporated in polymer matrix for various applications. This paper reviews the vanillin Schiff base chelates their complexes and their applications.

Schiff bases are versatile ligands which are synthesized from the condensation of primary amines with carbonyl groups. These compounds are very important in medicinal and pharmaceutical fields because of their wide spectrum of biological activities. Most of them show biological activities such as antibacterial, antifungal as well as antitumor activity. Transition metal complexes derived from the Schiff base ligands with biological activity have been widely studied. This summarizes the synthesis and biological activities of Schiff bases and its transition complexes.

Salt deposition has an extremely negative impact on pipeline safety. It can cause local corrosion of pipes metal, which leads to their rapid destruction and creates a fire hazard in the pipelines. The number of failures in oil and gas industry is due to the development of local corrosion in pipelines and is a big part of total accidents. The situation is aggravated by the fact that it is very difficult in practice to identify local corrosion areas of pipelines. The salt layer increases energy consumption during oil transportation and this leads to significant economic losses. Salt deposition occurs during all well operation methods, but the most negative consequences of salt deposition are observed when oil production is carried out by electric submersible pumps (ESP). These types of pumps are highly sensitive to calcium carbonate scales, because high pressure and temperature sufficiently contributes to the deposition of CaCO3 .

Mono and bi-organometallic complexes of Cu(II), Ni(II), Mn(II), Zn(II) and Ag(I) complexes with oxaloamide ligand has much potential as therapeutic and diagnostic agents. The ligand allows the thermodynamic and kinetic reactivity of the metal ion to be controlled and also provide a scaffold for functionalization. Specific examples involving the design of metal complexes as anticancer agents are discussed. These complexes have been synthesized and characterized by (1H-NMR, mass, IR, UV-VIS, ESR) spectra, magnetic moments and conductance measurements, elemental and thermal analyses. Molar conductances in DMF solution indicates that, the complexes are non-electrolytes. The ESR spectra of solid Cu(II) complexes (2-5) show an axial type indicating a d(X2-y2) ground state with a significant covalent bond character. However, Mn(II) complex(9), shows an isotropic type indicating an octahedral geometry. Cytotoxic evolution IC50 of the ligand and its complexes have been carried out. Cu(II) Complexes show enhanced activity in comparison to the parent ligand or standard drug. Copper is enriched in various human cancer tissues and is a co-factor essential for tumor angiogenesis processes. However, the use of copper binding ligand to target tumor, copper could provide a novel strategy for cancer selective treatment.

Three benzene-1,3-disulfonamide derivatives were investigated for their interaction with 12 mammalian α-carbonic anhydrases (CAs, EC 4.2.1.1), and three bacterial/archaeal CAs belonging to the α-, β-, and γ-CA class, respectively. X-ray crystal structure of the three inhibitors in complex with the dominant human isozyme CA II revealed a particular binding mode within the cavity. The sulfonamide group in meta-position to the Zn2+-coordinated SO2NH2 moiety was oriented toward the hydrophilic side of the active site cleft, establishing hydrogen bonds with His64, Asn67, Gln92, and Thr200. The plane of the phenyl moiety of the inhibitors was rotated by 45° and tilted by 10° with respect to its most recurrent orientation in other CA II–sulfonamide complexes.

Cu(II) complexes have been synthesized from different Schiff bases, such as 3-((2-hydroxy phenylimino)methyl)-4H-chromen-4-one (HL(1)), 2-((4-oxo-4H-chromen-3-yl)methylneamino) benzoicacid (HL(2)), 3-((3-hydroxypyridin-2-ylimino)methyl)-4H-chromen-4-one (HL(3)) and 3-((2-mercaptophenylimino)methyl)-4H-chromen-4-one (HL(4)). The complexes were characterized by analytical, molar conductance, IR, electronic, magnetic, ESR, thermal, powder XRD and SEM studies. The analytical data reveal that metal to ligand molar ratio is 1:2 in all the complexes. Molar conductivity data indicates that all the Cu(II) complexes are neutral. On the basis of magnetic and electronic spectral data, distorted octahedral geometry is proposed for all the Cu(II) complexes. Thermal behaviour of the synthesized complexes illustrates the presence of lattice water molecules in the complexes. X-ray diffraction studies reveal that all the ligands and their Cu(II) complexes have triclinic system with different unit cell parameters. Antimicrobial, antioxidant and DNA cleavage activities indicate that metal complexes exhibited greater activity as compared with ligands.

The structure study of five Schiff bases derived from L-arginine (L-Arg) and 2-hydroxy carbonyl compounds were performed in both solution and solid state using NMR and X-ray methods. Both analytical methods applied to the solid state sample of two Schiff bases showed a ignificant difference in molecular structures of unsubstituted and 7-CH3 substituted compounds. This effect was explained as a steric interaction of methyl group. Additionally the structure of two Cd2+ complexes with some Schiff bases were determined by NMR methods in DMSO solution and in the solid state. On the base of heteronuclear NMR measurement (13C, 15N and 113Cd) it was possible to define the complexation site on nitrogen atom. The large set of spectral parameters: chemical shifts, homo- and heteronuclear coupling constants, were used in structure study.

Synthesis, growth, X-ray crystal structure and characterization of a novel third order nonlinear optical material, 4-methoxy-4'-dimethylamino-benzylidene aniline (MDMABA), are reported for the first time. The asymmetric unit of MDMABA compound contains two crystallographically independent molecules (A and B), and they exist in the E-configuration. The structural perfection of the grown crystal is analyzed by high-resolution X-ray diffraction rocking curve analysis. The functional groups present in MDMABA are investigated by FTIR and FT-Raman spectral analyses. The placement of the protons is determined using HNMR spectrum. The range and percentage of optical transmission were ascertained by recording UV-vis-NIR spectrum. Thermal and mechanical properties are reported. Dielectric study shows that the dielectric constant of the crystal varies with frequency and temperature. The third order nonlinear optical absorption coefficient of the MDMABA crystal is determined by the Z-scan t...