Deprotonated Schiff Base Research Articles

Studies on a novel oxo-vanadium(V) complex of a tridentate ONO Schiff base ligand: Synthesis, characterization, X-ray crystal structure, Hirshfeld surface analysis, biological and catalytic activity

This study reports the successful synthesis and characterization of a novel oxovanadium(V) complex, [VO(L)(MeOH)(MeO)], prepared from 2-hydroxy-3-methoxybenzaldehyde and 2-methyl-3-aminoquinazoline. To elucidate the structure of the complex, we employed comprehensive characterization techniques such as CHN analysis, molar conductivity measurements, FT-IR, 1H NMR, UV-Vis spectroscopy, and single-crystal X-ray diffraction. The X-ray analysis confirmed an octahedral geometry around the V(V) center, coordinated with donor atoms from the deprotonated Schiff base ligand, an oxido group, a methanol molecule, and a methoxy group. Hirshfeld surface analysis was employed to evaluate intermolecular interactions.Furthermore, the complex exhibited impressively efficient catalytic activity in glucose oxidation under mild conditions (aqueous solution, room temperature, O2 oxidant), achieving a conversion rate of 98 %. Additionally, the antibacterial activity of the ligand and complex against various bacterial strains, including Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus cereus, was evaluated. The results demonstrated promising antibacterial potential of the [VO(L)(MeOH)(MeO)] complex, particularly against E. coli, P. aeruginosa, and B. cereus. These findings suggest potential applications of this new oxovanadium(V) complex in both catalysis and antibacterial treatments.

Structural basis for the allosteric modulation of rhodopsin by nanobody binding to its extracellular domain

Rhodopsin is a prototypical G protein-coupled receptor (GPCR) critical for vertebrate vision. Research on GPCR signaling states has been facilitated using llama-derived nanobodies (Nbs), some of which bind to the intracellular surface to allosterically modulate the receptor. Extracellularly binding allosteric nanobodies have also been investigated, but the structural basis for their activity has not been resolved to date. Here, we report a library of Nbs that bind to the extracellular surface of rhodopsin and allosterically modulate the thermodynamics of its activation process. Crystal structures of Nb2 in complex with native rhodopsin reveal a mechanism of allosteric modulation involving extracellular loop 2 and native glycans. Nb2 binding suppresses Schiff base deprotonation and hydrolysis and prevents intracellular outward movement of helices five and six – a universal activation event for GPCRs. Nb2 also mitigates protein misfolding in a disease-associated mutant rhodopsin. Our data show the power of nanobodies to modulate the photoactivation of rhodopsin and potentially serve as therapeutic agents for disease-associated rhodopsin misfolding.

Twisting and Protonation of Retinal Chromophore Regulate Channel Gating of Channelrhodopsin C1C2.

Channelrhodopsins (ChRs) are light-gated ion channels and central optogenetic tools that can control neuronal activity with high temporal resolution at the single-cell level. Although their application in optogenetics has rapidly progressed, it is unsolved how their channels open and close. ChRs transport ions through a series of interlocking elementary processes that occur over a broad time scale of subpicoseconds to seconds. During these processes, the retinal chromophore functions as a channel regulatory domain and transfers the optical input as local structural changes to the channel operating domain, the helices, leading to channel gating. Thus, the core question on channel gating dynamics is how the retinal chromophore structure changes throughout the photocycle and what rate-limits the kinetics. Here, we investigated the structural changes in the retinal chromophore of canonical ChR, C1C2, in all photointermediates using time-resolved resonance Raman spectroscopy. Moreover, to reveal the rate-limiting factors of the photocycle and channel gating, we measured the kinetic isotope effect of all photoreaction processes using laser flash photolysis and laser patch clamp, respectively. Spectroscopic and electrophysiological results provided the following understanding of the channel gating: the retinal chromophore highly twists upon the retinal Schiff base (RSB) deprotonation, causing the surrounding helices to move and open the channel. The ion-conducting pathway includes the RSB, where inflowing water mediates the proton to the deprotonated RSB. The twisting of the retinal chromophore relaxes upon the RSB reprotonation, which closes the channel. The RSB reprotonation rate-limits the channel closing.

Functional characterization of xanthorhodopsin in Salinivibrio socompensis, a novel halophile isolated from modern stromatolites.

A putative xanthorhodopsin-encoding gene, XR34, was found in the genome of the moderately halophilic gammaproteobacterium Salinivibrio socompensis S34, isolated from modern stromatolites found on the shore of Laguna Socompa (3570m), Argentina Puna. XR-encoding genes were clustered together with genes encoding X-carotene, retinal (vitamin-A aldehyde), and carotenoid biosynthesis enzymes while the carotene ketolase gene critical for the salinixanthin antenna compound was absent. To identify its functional behavior, we herein overexpressed and characterized this intriguing microbial rhodopsin. Recombinant XR34 showed all the salient features of canonical microbial rhodopsin and covalently bound retinal as a functional chromophore with λmax = 561nm (εmax ca. 60,000M-1cm-1). Two canonical counterions with pK values of around 6 and 3 were identified by pH titration of the recombinant protein. With a recovery time of approximately half an hour in the dark, XR34 shows light-dark adaptation shifting the absorption maximum from 551 to 561nm. Laser-flash induced photochemistry at pH 9 (deprotonated primary counterion) identified a photocycle starting with a K-like intermediate, followed by an M-state (λmax ca. 400nm, deprotonated Schiff base), and a final long wavelength-absorbing N- or O-like intermediate before returning to the parental 561nm-state. Initiating the photocycle at pH 5 (protonated counterion) yields only bathochromic intermediates, due to the lacking capacity of the counterion to accept the Schiff base proton. Illumination of the membrane-embedded protein yielded a capacitive transport current. The presence of the M-intermediate under these conditions was demonstrated by a blue light-induced shunt process.

Schiff Base in Ketoamine Form and Rh(η4-cod)-Schiff Base Complex with Z' = 2 Structure from Pairwise C-H···Metallochelate-π Contacts.

Condensation of 2-hydroxybenzaldehyde (salicylaldehyde) or 2-hydroxy-1-naphthaldehyde with 2-ethylaniline yields the Schiff base compound of (E)-2-(((2-ethylphenyl)imino)methyl)phenol (HL1) or (E)-1-(((2-ethylphenyl)imino)methyl)naphthalen-2-ol (HL2), which in turn react with the dinuclear complex of [Rh(η4-cod)(µ-O2CCH3)]2 (cod = cycloocta-1,5-diene) to afford the mononuclear (η4-cod){(E)-2-(((2-ethylphenyl)imino)methyl)phenolato-κ2N,O}rhodium(I), [Rh(η4-cod)(L1)] (1) or (η4-cod){(E)-1-(((2-ethylphenyl)imino)methyl)naphthalen-2-olato-κ2N,O}rhodium(I), [Rh(η4-cod)(L2)] (2) (L1 or L2 = deprotonated Schiff base ligand). The X-ray structure determination revealed that the HL2 exists in the solid state not as the usual (imine)N···H-O(phenol) form (enolamine form) but as the zwitterionic (imine)N-H+···-O(phenol) form (ketoamine form). 1H NMR spectra for HL2 in different solvents demonstrated the existence of keto-enol tautomerism (i.e., keto ⇆ enol equilibrium) in solution. The structure for 1 and 2 showed that the deprotonated Schiff base ligand coordinates to the Rh(η4-cod)-fragment as a six-membered N^O-chelate around the rhodium atom with a close-to-square-planar geometry. Two symmetry-independent molecules (with Rh1 and Rh2) were found in the asymmetric unit in 1 in a structure with Z' = 2. The supramolecular packing in HL2 was organized by π-π and C-H···π contacts, while only two recognized C-H···π contacts were revealed in 1 and 2. Remarkably, there were reciprocal or pairwise C-H···π contacts between a pair of each of the symmetry-independent molecules in 1. This pairwise C-H contact to the Rh-N^O chelate (metalloaromatic) ring may be a reason for the two symmetry-independent molecules in 1. Differential scanning calorimetry (DSC) analyses revealed an irreversible phase transformation from the crystalline-solid to the isotropic-liquid phase and subsequently confirmed the thermal stability of the compounds. Absorption spectra in solution were explained by excited state properties from DFT/TD-DFT calculations.

Theoretical investigation of the photocycle dynamics of the Archaerhodopsin 3 based fluorescent voltage sensor Archon2

Previously the retinal photocycle dynamics of the fluorescent voltage sensor Archon2, a mutant of Archaerhodopsin 3, in pH 8 Tris buffer was studied experimentally at room temperature by photo-excitation (excitation wavelengths 590 nm and 632.8 nm) of the protonated retinal Schiff base (PRSB) Ret_586 (absorption maximum at λmax = 586 nm) and following the absorption spectra development during and after light exposure.In this paper the experimental results are simulated numerically with developed photocycle schemes and relevant dynamics parameters are extracted.Photo-excitation of fresh thawed (dark-adapted) Archon2 (Archon2da) caused photoisomerization of Ret_586 (Ret_586da) to Ret_553 (Ret_535da, main component, absorption maximum at 553 nm) and to Ret_485 (Ret_485da, minor component) in a primary excitation process (primary photocycle). Ret_485 does not absorb at λexc = 590 nm or 632.8 nm and therefore is not involved in further photo-excitation. Continued light exposure transformed Archon2da to light-adapted Archon2la with secondary photocycle dynamics changing Ret_553 (Ret_535da) to Ret_535 (Ret_535la, absorption maximum at 535 nm). Ret_535la backward photo-isomerized to Ret_586 in light-adapted state (named Ret_586la) and partly deprotonated to neutral retinal Schiff base (RSB) Ret_372 in light adapted state (named Ret_372la, same isomer form as Ret_535).After excitation light switch-off Archon2la recovered in the dark to Archon2da with recovery of Ret_372la to Ret_372da, Ret_535la to Ret_535da, and Ret_586la to Ret_586da. Ret_372da slowly re-protonated to Ret_535da, and Ret_535da slowly isomerized back to Ret_586da. The long-time dynamics in the dark at room temperature changed over to thermal Archon2 denaturation accompanied with protonated retinal Schiff base deprotonation.

Unusual Photoisomerization Pathway in a Near-Infrared Light Absorbing Enzymerhodopsin.

Microbial and animal rhodopsins possess retinal chromophores which capture light and normally photoisomerize from all-trans to 13-cis and from 11-cis to all-trans-retinal, respectively. Here, we show that a near-infrared light-absorbing enzymerhodopsin from Obelidium mucronatum (OmNeoR) contains the all-trans form in the dark but isomerizes into the 7-cis form upon illumination. The photoproduct (λmax = 372 nm; P372) possesses a deprotonated Schiff base, and the system exhibits a bistable nature. The photochemistry of OmNeoR was arrested at <270 K, indicating the presence of a potential barrier in the excited state. Formation of P372 is accompanied by protonation changes of protonated carboxylic acids and peptide backbone changes of an α-helix. Photoisomerization from the all-trans to 7-cis retinal conformation rarely occurs in any solvent and protein environments; thus, the present study reports on a novel photochemistry mediated by a microbial rhodopsin, leading from the all-trans to 7-cis form selectively.

QuasAr Odyssey: the origin of fluorescence and its voltage sensitivity in microbial rhodopsins

Rhodopsins had long been considered non-fluorescent until a peculiar voltage-sensitive fluorescence was reported for archaerhodopsin-3 (Arch3) derivatives. These proteins named QuasArs have been used for imaging membrane voltage changes in cell cultures and small animals. However due to the low fluorescence intensity, these constructs require use of much higher light intensity than other optogenetic tools. To develop the next generation of sensors, it is indispensable to first understand the molecular basis of the fluorescence and its modulation by the membrane voltage. Based on spectroscopic studies of fluorescent Arch3 derivatives, we propose a unique photo-reaction scheme with extended excited-state lifetimes and inefficient photoisomerization. Molecular dynamics simulations of Arch3, of the Arch3 fluorescent derivative Archon1, and of several its mutants have revealed different voltage-dependent changes of the hydrogen-bonding networks including the protonated retinal Schiff-base and adjacent residues. Experimental observations suggest that under negative voltage, these changes modulate retinal Schiff base deprotonation and promote a decrease in the populations of fluorescent species. Finally, we identified molecular constraints that further improve fluorescence quantum yield and voltage sensitivity.

Proton transfer reactions in donor site mutants of ESR, a retinal protein from Exiguobacterium sibiricum

Light-driven proton transport by microbial retinal proteins such as archaeal bacteriorhodopsin involves carboxylic residues as internal proton donors to the catalytic center which is a retinal Schiff base (SB). The proton donor, Asp96 in bacteriorhodopsin, supplies a proton to the transiently deprotonated Schiff base during the photochemical cycle. Subsequent proton uptake resets the protonated state of the donor. This two step process became a distinctive signature of retinal based proton pumps. Similar steps are observed also in many natural variants of bacterial proteorhodopsins and xanthorhodopsins where glutamic acid residues serve as a proton donor. Recently, however, an exception to this rule was found. A retinal protein from Exiguobacterium sibiricum, ESR, contains a Lys residue in place of Asp or Glu, which facilitates proton transfer from the bulk to the SB. Lys96 can be functionally replaced with the more common donor residues, Asp or Glu. Proton transfer to the SB in the mutants containing these replacements (K96E and K96D/A47T) is much faster than in the proteins lacking the proton donor (K96A and similar mutants), and in the case of K96D/A47T, comparable with that in the wild type, indicating that carboxylic residues can replace Lys96 as proton donors in ESR. We show here that there are important differences in the functioning of these residues in ESR from the way Asp96 functions in bacteriorhodopsin. Reprotonation of the SB and proton uptake from the bulk occur almost simultaneously during the M to N transition (as in the wild type ESR at neutral pH), whereas in bacteriorhodopsin these two steps are well separated in time and occur during the M to N and N to O transitions, respectively.

Calcium Binding to TAT Rhodopsin.

Rhodopsin is a large family of retinal-binding photoreceptive proteins found in animals and microbes. The retinal chromophore is normally positively charged by protonation of the Schiff base linkage, which is stabilized by the negatively charged counterion(s) such as aspartates, glutamates, and chloride ions. In contrast, no cation binding was reported near the retinal chromophore under physiological pH, presumably because of the electrostatic repulsion. Sodium binding takes place in light-driven sodium pumps, but the binding near the retinal chromophore is a transient event. Here, we report Ca2+ binding to a wild-type microbial rhodopsin, which is achieved for the neutral retinal chromophore with a deprotonated Schiff base. TAT rhodopsin from marine bacteria contains protonated and deprotonated retinal Schiff bases at physiological pH (pH ∼ 8), which absorb visible and UV light, respectively. We observed that the equilibrium shifted toward the deprotonated state upon increasing Ca2+ concentration, and the Kd value was determined to be 0.17 mM. Site-directed mutagenesis study showed that E54 and D227 constitute the binding site of Ca2+. ATR-FTIR spectroscopy revealed secondary structural changes upon Ca2+ binding to E54 and D227, while they are negatively charged with or without Ca2+ binding.

Azide-Coordination in Homometallic Dinuclear Lanthanide(III) Complexes Containing Nonequivalent Lanthanide Metal Ions: Zero-Field SMM Behavior in the Dysprosium Analogue.

A series of homometallic dinuclear lanthanide complexes containing nonequivalent lanthanide metal centers [Ln2(LH2)(LH)(CH3OH)(N3)]·xMeOH·yH2O [1, Ln = DyIII, x = 0, y = 2; 2, Ln = TbIII, x = 1, y = 1] have been synthesized [LH4 = 6-((bis(2-hydroxyethyl)amino)-N'-(2-hydroxybenzylidene)picolinohydrazide] and characterized. The dinuclear assembly contains two different types of nine-coordinated lanthanide centers, because the nonequivalent binding of the azide co-ligand as well as the varying coordination of the deprotonated Schiff base ligand. Detailed magnetic studies have been performed on the complexes 1 and 2. Complex 1 and its diluted analogue (15%) are zero-field SMMs with effective energy barriers (Ueff) of magnetization reversal equal to 59(3) K and 66(3) K and relaxation times of τ0 = 10(4) × 10-6 s and 10(4) × 10-8 s, respectively. On the other hand, complex 2 shows a field-induced SMM behavior. Combined ab initio and density functional theory calculations were performed to explain the experimental findings and to unravel the nature of the magnetic anisotropy, exchange-coupled spectra, and magnetic exchange interactions between the two lanthanide centers.

Optical Switching Between Long-lived States of Opsin Transmembrane Voltage Sensors.

Opsin‐based transmembrane voltage sensors (OTVSs) are membrane proteins increasingly used in optogenetic applications to measure voltage changes across cellular membranes. In order to better understand the photophysical properties of OTVSs, we used a combination of UV‐Vis absorption, fluorescence and FT‐Raman spectroscopy to characterize QuasAr2 and NovArch, two closely related mutants derived from the proton pump archaerhodopsin‐3 (AR3). We find both QuasAr2 and NovArch can be optically cycled repeatedly between O‐like and M‐like states using 5‐min exposure to red (660 nm) and near‐UV (405 nm) light. Longer red‐light exposure resulted in the formation of a long‐lived photoproduct similar to pink membrane, previously found to be a photoproduct of the BR O intermediate with a 9‐cis retinylidene chromophore configuration. However, unlike QuasAr2 whose O‐like state is stable in the dark, NovArch exhibits an O‐like state which slowly partially decays in the dark to a stable M‐like form with a deprotonated Schiff base and a 13‐cis,15‐anti retinylidene chromophore configuration. These results reveal a previously unknown complexity in the photochemistry of OTVSs including the ability to optically switch between different long‐lived states. The possible molecular basis of these newly discovered properties along with potential optogenetic and biotechnological applications are discussed.

Synthesis and Structural Characterization of (E)-4-[(2-Hydroxy-3-methoxybenzylidene)amino]butanoic Acid and Its Novel Cu(II) Complex

A novel Cu(II) complex based on the Schiff base obtained by the condensation of ortho-vanillin with gamma-aminobutyric acid was synthesized. The compounds are physico-chemically characterized by elemental analysis, HR-ESI-MS, FT-IR, and UV-Vis. The complex and the Schiff base ligand are further structurally identified by single crystal X-ray diffraction and 1H and 13C-NMR, respectively. The results suggest that the Schiff base are synthesized in excellent yield under mild reaction conditions in the presence of glacial acetic acid and the crystal structure of its Cu(II) complex reflects an one-dimensional polymeric compound. The molecular structure of the complex consists of a Cu(II) ion bound to two singly deprotonated Schiff base bridging ligands that form a CuN2O4 chelation environment, and a coordination sphere with a disordered octahedral geometry.

Synthesis, Spectral Characterization and Biological Evaluation of Metal Complexes of 2-Thioxoquinoline Aminophenol

A series of novel 2-thioxoquinoline aminophenol Schiff base based Co(II), Ni(II), Cu(II) and Zn(II) metal complexes [M(L)2], (M = Co2+, Ni2+, Cu2+ &amp; Zn2+; L = 2-thioxoquinoline aminophenol) were synthesized and characterized by elemental analysis and spectral studies (FT-IR, UV-Vis, 1H NMR, ESR and ESI-Mass). All experimental results showed that in these metal complexes, the central metal atom was coordinated by oxygen, nitrogen and sulfur donor atoms of deprotonated Schiff base. Further, the ligand and its metal(II) complexes were screened against Gram-positive (Staphylococcus aureus), Gram-negative (Escherichia coli) bacteria and fungus (Candida albicans) strains. in vitro Anticancer activity of ligand and its metal(II) complexes were also screened against HeLa cells (Human cervical cancer cells).

Synthesis, crystal structures, magnetic and magnetocaloric studies of heterometallic enneanuclear {Cu7Gd2} complexes

The reaction of Gd(NO3)3·6H2O and [Cu2(piv)4(pivH)2] with the polydentate Schiff base ligands o-OH-C10H6-CH = NC(R)(CH2OH)2 (R = CH3, H3L1; R = C2H5, H3L2) in MeOH afforded the enneanuclear heterometallic complexes [Cu7Gd2(L1)4(HL1)2(piv)4(H2O)(MeOH)3] (1) and [Cu7Gd2(L2)4(HL2)2(piv)4(MeOH)5] (2). Crystallographic studies revealed that both complexes are isostructural and consist of a central core {Cu7Gd2(μ3-Oalkoxo)6(μ2-Oalkoxo)4(μ2-Opivalato)2}8+. Peripheral ligation and bridging are provided by four triply and two doubly deprotonated Schiff base ligands, two μ3-pivalates, two chelate pivalates, and terminal aqua and/or MeOH molecules. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic intramolecular interactions in both complexes. The magnetocaloric effect of 1 and 2 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was found equal to 13.3 and 12.1 Jkg-1K−1 for 1 and 2, respectively, at 2 K for ΔH = 5 T.

The Colorimetric Signaling of Water Content by a Deprotonated Schiff Base in some Aprotic Organic Solvents

AbstractA simple Schiff base, (E)‐2‐[1‐{2‐(2,4‐dinitrophenyl)hydrazono}ethyl]phenol (Hdph) and its deprotonated form, (E)‐1‐(2,4‐dinitrophenyl)‐2‐{1‐(2‐hydroxyphenyl)ethylidene} hydrazine‐1‐ide (dph) have been synthesized and characterized by various physicochemical and spectroscopic techniques. Their structures have also been determined by single‐crystal X‐ray crystallography. The dph has been utilized as a colorimetric probe for the signaling of water content in some water‐miscible aprotic organic solvents (acetonitrile and tetrahydrofuran). The dph reveals a pronounced colorimetric behavior in response to the variation of water content in these solvents. Significant changes in UV‐visible absorption spectra permit a ratiometric analysis of the signaling behavior. The spectral changes are pronounced for the water content of less than 10 %, which is suitable for the application of dph as a receptor for the determination of water content in binary aqueous organic solvents having lower water content. The limit of detection (LOD) for water content in acetonitrile and tetrahydrofuran is calculated as 0.20 % and 0.28 %, respectively.

Schiff base and azido coordinated di-/poly-nuclear cadmium(II) complexes: Crystal structure, photocatalytic degradation of methylene blue and thermal analysis

Two Schiff base coordinated cadmium(II) complexes, namely [Cd(H4L1)(N3)2]n (1) and [Cd2(L2)(N3)2]·(H2O) (2) (where H4L1 = 2-((2-hydroxy-3-methoxybenzylidene)amino)-2-(hydroxymethyl)-propane-1,3-diol; and H2L2 = bis((3-methoxysalicylidene)ethyl)ethylamine), were synthesized and characterized by X-ray single crystal diffraction. Both the complexes 1 and 2 crystallize in monoclinic system with space group P 21/n. Complex 1 is a 1D coordination polymer where Cd(H4L1) species are doubly connected by bridging μ-1,1 azide anions. Complex 2 is a discrete dinuclear compound where the double deprotonated Schiff base (L2)2− acts as a two compartmental ligand coordinating two cadmium atoms. Photocatalytic activity of the complexes has been studied using UV–vis absorption spectroscopic technique and the results show that both the complexes are active for photocatalytic degradation of methylene blue (MB) in presence of UV light, and within 180 min MB decomposed by 37.64% and 32.60% in presence of complexes 1 and 2, respectively.

A novel Cu(II) distorted cubane complex containing Cu4O4 core as the first tetranuclear catalyst for temperature dependent oxidation of 3,5-di-tert-butyl catechol and in interaction with DNA & protein (BSA).

The tri-dentate Schiff base ligand 3-(2-hydroxyethylimino)-1-phenylbut-1-en-1-ol (L) produced the tetra-nuclear Cu(II) distorted cubane complex which contain Cu4O4 core, upon reaction with Cu(II)acetate.H2O. The complex was structurally characterized by X-ray crystallography and found that, in this tetrameric and tetra-nuclear distorted cubane structure, each two-fold deprotonated Schiff base ligand coordinated to a Cu(II) center with their alcoholic oxygens and imine nitrogens and formed six and five-membered chelate rings. At the same time, each ligand bridged to a neighboring Cu(II) atom by its alcoholic oxygen, thus the metal centers became penta-coordinated. The copper(II) complex with μ-ɳ2-hydroxo bridges and Cu….Cu distance about 3 Å was structurally similar to the active site of natural catechol oxidase enzyme and exhibited excellent catecholase activity in aerobic oxidation of 3,5-di-tert-butyl catechol to its o-quinone. The kinetics and mechanism of the oxidation of 3, 5-DTBCH2 catalyzed by [CuL]4 complex, were studied at four different temperatures from 283 to 313K by UV-Vis spectroscopy. Interaction of [CuL]4 complex with FS-DNA was investigated by UV-Vis and fluorescence spectroscopy, viscosity measurements, cyclic voltammetry (CV), circular dichroism (CD) and agarose gel electrophoresis. The main mode of binding of the complexes with DNA was intercalation. The interaction between [CuL]4 complex and bovine serum albumin (BSA) was studied by UV-Vis, fluorescence and synchronous fluorescence spectroscopic techniques. The results indicated a high binding affinity of the complex to BSA. Invitro anticancer activity of the complex was evaluated against A549, Jurkat and Ragi cell lines by MTT assay. The complex was remarkably active against the cell lines and can be a good candidate for an anticancer drug. Theoretical docking studies were performed to further investigate the DNA and BSA binding interactions.

Two organic–inorganic hybrid Schiff base copper materials: synthesis and their catalytic properties for constructing C–N bonds

Two Schiff base copper complexes: [Cu(H2O)2(HL1)]·2H2O (1) (H3L1 =2-((2,4-dihydroxybenzylidene)amino)acetic acid) and [Cu(L2) (CH3OH)]4 (2) (H2L2 = 3-phenyl-2-(2-hydroxy-5-chlorobenzylideneamino)propane-1-ol), have been simply synthesized and fully characterized. Single crystal X-ray diffraction (SXRD) revealed that 1 consists of one five-coordinated copper atom and one deprotonated Schiff base ligand HL1. The copper atom in 1 showed the distorted tetragonal pyramid geometry, whereas, four copper atoms in 2 were six-coordinated and exhibited the distorted octahedron geometry. Importantly, two Schiff base complexes were further used as catalysts in Chan–Lam coupling reaction and 2 demonstrated excellent catalytic performance in construction of C–N bonds (yields up to 87%).

Synthesis, characterization, crystal structure, and electrochemical properties of three copper(II) complexes with 3,5-dihalosalicylaldehyde Schiff bases derived from amantadine

Complexes 1-3, C34H36X4CuN2O2 (X = Cl, Br, I), were synthesized with copper chloride dihydrate and three new Schiff base ligands derived from amantadine and 3,5-dihalosalicylaldehydes. They were characterized by IR, UV–VIS, elemental analysis, molar conductance, and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis reveals that 1 and 2 crystallize in the triclinic system, Pī space group. Each asymmetric unit consists of one copper(II) ion, two corresponding deprotonated Schiff base ligands and one lattice dichloromethane molecule. 3 crystallizes in the monoclinic system, P21/n space group. Each asymmetric unit consists of one copper(II) ion and two deprotonated iodo- Schiff base ligands. The tetra-coordination of the central copper(II) ion in 1-3 is constructed by two nitrogen atoms and two oxygen atoms from the corresponding Schiff base ligands, forming a distorted tetrahedral geometry. Electrochemical properties of the complexes were determined by cyclic voltammetry.