Metal complexes as enzyme inhibitors

Synthesis, structures and biomolecular interactions of new silver(i) 5,5-diethylbarbiturate complexes of monophosphines targeting Gram-positive bacteria and breast cancer cells

New silver(i) 5,5-diethylbarbiturate complexes exhibit very high antimicrobial activity against Gram-positive bacteria and kill MCF-7 cells, damaging mitochondria and DNA.

Aluminium sulfate exposure: A set of effects on hydrolases from brain, muscle and digestive tract of juvenile Nile tilapia (Oreochromis niloticus)

Aluminium is a major pollutant due to its constant disposal in aquatic environments through anthropogenic activities. The physiological effects of this metal in fish are still scarce in the literature. This study investigated the in vivo and in vitro effects of aluminium sulfate on the activity of enzymes from Nile tilapia (Oreochromis niloticus): brain acetylcholinesterase (AChE), muscle cholinesterases (AChE-like and BChE-like activities), pepsin, trypsin, chymotrypsin and amylase. Fish were in vivo exposed during 14days when the following experimental groups were assayed: control group (CG), exposure to Al₂(SO₄)₃ at 1μg·mL^-1 (G1) and 3μg·mL^-1 (G3) (concentrations compatible with the use of aluminium sulfate as coagulant in water treatment). In vitro exposure was performed using animals of CG treatment. Both in vivo and in vitro exposure increased cholinesterase activity in relation to controls. The highest cholinesterase activity was observed for muscle BChE-like enzyme in G3. In contrast, the digestive enzymes showed decreased activity in both in vivo and in vitro exposures. The highest inhibitory effect was observed for pepsin activity. The inhibition of serine proteases was also quantitatively analyzed in zymograms using pixel optical densitometry as area under the peaks (AUP) and integrated density (ID). These results suggest that the inhibition of digestive enzymes in combination with activation of cholinesterases in O. niloticus is a set of biochemical effects that evidence the presence of aluminium in the aquatic environment. Moreover, these enzymatic alterations may support further studies on physiological changes in this species with implications for its neurological and digestive metabolisms.

Antimicrobial Activity and Urease Inhibition of Schiff Bases Derived from Isoniazid and Fluorinated Benzaldehydes and of Their Copper(II) Complexes

In order to evaluate the influence of substitution on biological properties of Schiff bases and their metal complexes, a series of differently substituted fluorine-containing Schiff bases starting from the drug isoniazid (isonicotinylhydrazide) were prepared and their structures were established by single-crystal X-ray diffraction. Also, four copper(II) complexes of these Schiff bases were synthesized. The prepared compounds were evaluated for their antimicrobial activity and urease inhibition. Two of the Schiff bases exerted activity against C. albicans. All copper(II) complexes showed excellent inhibitory properties against jack bean urease, considerably better than that of the standard inhibitor acetohydroxamic acid.

Tungsten Oxide Nanoplates; the Novelty in Targeting Metalloproteinase-7 Gene in Both Cervix and Colon Cancer Cells

In this study, we synthesized tungsten oxide (WO₃) nanoplates, both crystallographic phases and the morphology of the samples were determined by powder x-ray diffraction and the scanning electron microscopy, respectively. The obtained data clarified that, the all prepared WO₃·H₂O samples were composed of large quantity of nanoplates. The cytotoxicity patterns of nanoplates were checked on both normal and cancer mammalian cell lines. Both nanoplates cytotoxicity did not exceed the 50 % inhibitory concentration (IC50) on the all normal tested cells even by using concentrations up to 1 mg/ml. In addition, orthorhombic tungsten oxide nanoplate was more potent against both Caco2 and Hela cells by showing inhibition percentages in cellular viability 64.749 and 72.27, respectively, and with cancer selectivity index reached 3.2 and 2.6 on both colon and cervix cancer, respectively. The anticancer effects of nanoplates were translated to alteration in both pro-apoptotic and anti-apoptotic genes expressions. Tungsten oxide nanoplates down regulated the expression of B cell lymphoma 2 (Bcl-2) and metalloproteinase-7 (MMP7) genes. In addition, orthorhombic tungsten oxide nanoplates showed more potentiation in IL2 and IL8 induction (40.43 pg/ml) and upregulation of TNF-α gene expression but with lower folds than Escherichia coli lipopolysaccharide (LPS) induction.

Biological activities of Zn(II)-S-methyl-cysteine complex as antiradical, inhibitor of acid phosphatase enzyme and in vivo antidepressant effects

The antidepressant effect of simple Zn(II) salts has been proved in several animal models of depression. In this study, a coordination metal complex of Zn(II) having a sulfur containing ligand is tested as antidepressant for the first time. Forced swimming test method on male Wistar rats shows a decrease in the immobility and an increase in the swimming behavior after treatment with [Zn(S-Met)2] (S-Met=S-methyl-l-cysteine) being more effective and remarkable than ZnCl2. The thiobarbituric acid and the pyranine consumption (hydroxyl and peroxyl radicals, respectively) methods were applied to evaluate the antioxidant activity of S-Met and [Zn(S-Met)2] showing evidence of attenuation of hydroxyl but not peroxyl radicals activities. UV-vis studies on the inhibition of acid phosphatase enzyme (AcP) demonstrated that S-methyl-l-cysteine did not produce any effect but, in contrast, [Zn(S-Met)2] complex behaved as a moderate inhibitor. Finally, bioavailability studies were performed by fluorescence spectroscopy denoting the ability of the albumin to transport the complex.

Inhibition studies of Helicobacter pylori urease with Schiff base copper(ii) complexes

Nine new copper(ii) complexes derived from various Schiff bases were prepared. Five complexes show effective urease inhibitory activities. Complex5has the most effective activity against urease, with a mixed competitive inhibition mechanism.

Synthesis, structures and urease inhibitory activity of cobalt(III) complexes with Schiff bases

A series of new cobalt(III) complexes were prepared. They are [CoL(1)(py)3]·NO3 (1), [CoL(2)(bipy)(N3)]·CH3OH (2), [CoL(3)(HL(3))(N3)]·NO3 (3), and [CoL(4)(MeOH)(N3)] (4), where L(1), L(2), L(3) and L(4) are the deprotonated form of N'-(2-hydroxy-5-methoxybenzylidene)-3-methylbenzohydrazide, N'-(2-hydroxybenzylidene)-3-hydroxylbenzohydrazide, 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol, and N,N'-bis(5-methylsalicylidene)-o-phenylenediamine, respectively, py is pyridine, and bipy is 2,2'-bipyridine. The complexes were characterized by infrared and UV-Vis spectra, and single crystal X-ray diffraction. The Co atoms in the complexes are in octahedral coordination. Complexes 1 and 4 show effective urease inhibitory activities, with IC50 values of 4.27 and 0.35 μmol L(-1), respectively. Complex 2 has medium activity against urease, with IC50 value of 68.7 μmol L(-1). While complex 3 has no activity against urease. Molecular docking study of the complexes with Helicobacter pylori urease was performed.

Tuning cobalt(III) Schiff base complexes as activated protein inhibitors

Cobalt(III) Schiff base complexes ([Co(acacen)(L)2](+), where L = NH3) inhibit histidine-containing proteins through dissociative exchange of the labile axial ligands (L). This work investigates axial ligand exchange dynamics of [Co(acacen)(L)2](+) complexes toward the development of protein inhibitors that are activated by external triggers such as light irradiation. We sought to investigate ligand exchange dynamics to design a Co(III) complex that is substitutionally inert under normal physiological conditions for selective activation. Fluorescent imidazoles (C3Im) were prepared as axial ligands in [Co(acacen)(L)2](+) to produce complexes (CoC3Im) that could report on ligand exchange and, thus, complex stability. These fluorescent imidazole reporters guided the design of a new dinuclear Co(III) Schiff base complex containing bridging diimidazole ligands, which exhibits enhanced stability to ligand exchange with competing imidazoles and to hydrolysis within a biologically relevant pH range. These studies inform the design of biocompatible Co(III) Schiff base complexes that can be selectively activated for protein inhibition with spatial and temporal specificity.

Aluminum and its effect in the equilibrium between folded/unfolded conformation of NADH

Nicotinamide adenine dinucleotide (NADH) is one of the most abundant cofactor employed by proteins and enzymes. The molecule is formed by two nucleotides that can lead to two main conformations: folded/closed and unfolded/open. Experimentally, it has been determined that the closed form is about 2 kcal/mol more stable than the open formed. Computationally, a correct description of the NADH unfolding process is challenging due to different reasons: 1) The unfolding process shows a very low energy difference between the two conformations 2) The molecule can form a high number of internal hydrogen bond interactions 3) Subtle effects such as dispersion may be important. In order to tackle all these effects, we have employed a number of different state of the art computational techniques, including: a) well-tempered metadynamics, b) geometry optimizations, and c) Quantum Theory of Atoms in Molecules (QTAIM) calculations, to investigate the conformational change of NADH in solution and interacting with aluminum. All the results indicate that aluminum indeed favors the closed conformation of NADH, due mainly to the formation of a more rigid structure through key hydrogen bond interactions.

Mode of action of tin-based anti-proliferative agents: Biological studies of organotin(IV) derivatives of fatty acids

Some organotin(IV) carboxylates of the general formula RnSn(L)m [n=3, m=1, R=Me, Pr, Bu and Ph; n=2, m=2, R=Me, Bu and Oct; L=anion of lauric (HLA), stearic (HSA) and myristic acid (HMA)] have been synthesized and characterized by various spectroscopic studies. Tri- and diorganotin(IV) carboxylates adopt trigonal-bipyramidal and octahedral geometry around tin atom, respectively. They have been screened in vitro for anti-tumor activity against cancer cell lines of human origin, viz. MCF-7 (mammary), HEK-293 (kidney), PC-3 (prostate), HCT-15 (colon) and HepG-2 (liver). Enzyme assays viz. lipid peroxidase, glutathione peroxidase, glutathione reductase and total glutathione assay have been carried out to explore the cause of their cytotoxiciy. The results indicate that ROS (reactive oxygen species) generation may be responsible for their cytotoxicity but elevation in LDH (lactate dehydrogenase) suggests that necrosis cannot be excluded. Further, DNA (deoxyribonucleic acid) fragmentation, acridine orange and comet assay support the fact that the apoptosis is the main cause of cytotoxicity of organotin(IV) carboxylates, whereas the necrosis plays a minor role. The anti-inflammatory activity evaluation shows that the complexes possess moderate activity. Results of acute toxicity of the complexes have also been discussed.

Solid-phase synthesis as a platform for the discovery of new ruthenium complexes for efficient release of photocaged ligands with visible light

Ruthenium-based photocaging groups have important applications as biological tools and show great potential as therapeutics. A method was developed to rapidly synthesize, screen, and identify ruthenium-based caging groups that release nitriles upon irradiation with visible light. A diverse library of tetra- and pentadentate ligands was synthesized on polystyrene resin. Ruthenium complexes of the general formula [Ru(L)(MeCN)n](m+) (n = 1-3, m = 1-2) were generated from these ligands on solid phase and then cleaved from resin for photochemical analysis. Data indicate a wide range of spectral tuning and reactivity with visible light. Three complexes that showed strong absorbance in the visible range were synthesized by solution phase for comparison. Photochemical behavior of solution- and solid-phase complexes was in good agreement, confirming that the library approach is useful in identifying candidates with desired photoreactivity in short order, avoiding time-consuming chromatography and compound purification.

Detection of trace heavy metal ions in water by nanostructured porous Si biosensors

Specific and sensitive detection and quantification of heavy metals in real water using label-free optical biosensors.

DNA interaction, cytotoxicity, antibacterial and antituberculosis activity of oxovanadium(iv) complexes derived from fluoroquinolones and 4-hydroxy-5-((4-hydroxyphenyl)diazenyl)thiazole-2(3H)-thione

Oxovanadium complexes (5a–5g) with fluoroquinolone ligands and azodye rhodanine (3) were synthesized and the effect of different groups was studied, which displayed various biological and medicinal activities.

Coordination behavior and bio-potent aspects of Ni(II) with 2-aminobenzamide and some amino acid mixed ligands--Part II: Synthesis, spectral, morphological, pharmacological and DNA interaction studies

A series of novel bioactive mixed ligand Ni(II) complexes (1a-1d) have been synthesised by using 2-aminobenzamide (2AB) and some bio-relevant amino acid ligands. The synthesised Ni(II) complexes were structurally characterized by various physico-chemical and spectral studies. Elemental analysis and molar conductance values suggest that 1:1:1 stoichiometry with non-electrolytic nature. Based on the spectral studies, both the ligands act as bidentate and they chelate with Ni(II) ion via amino-NH2 and amido-O and deprotonated carboxylato-O and amino-NH2 atoms respectively to form a stable six, five membered chelate rings with mononuclear octahedral geometry. Thermal studies show the presence of coordinated water and acetate molecules in the coordination. The powder X-ray diffractogram and SEM pictograph imply that all the complexes have fine crystalline peaks with homogeneous surface morphology. In vitro antimicrobial and antioxidant studies indicate the complexes are more active than free 2-aminobenzamide ligand. The Ni(II)-2AB-gly/phe complexes (1a and 1d) show significant oxidative cleavage and DNA binding activities. Moreover, the 3D molecular modeling, analysis of the complexes has also been studied.

Heterologous expression and functional characterization of a novel cellulose-disruptive protein LeEXP2 from Lycopersicum esculentum

There has been little research reported on the synergism of plant expansins in cellulose hydrolysis because of the difficulty of heterologous expression. In this study, the expansin gene LeExp2 of Lycopersicum esculentum was expressed for the first time in Pichia pastoris to identify its function in vitro. The optimal expression level was obtained by adding PMSF and a commercial protease inhibitor, and the maximum expression level was 70.9 mg/L. The affinity-purified LeEXP2 displayed cellulose-weakening activity and synergism with cellulase, and the reducing sugar yield in the reaction mixture with LeEXP2 was 1.4-9.8-fold that of control. The optimum pH and temperature for reducing-sugar liberation by LeEXP2 and endoglucanase were pH 4.8 and 50 °C. Cu(2+) and Fe(2+) notably increased the synergistic activity of LeEXP2, and Co(2+) enhanced the activity of endoglucanase but failed to improve synergism. LeEXP2 exhibited a high level of robustness to reagents and heat, indicating its potential application for cellulose decomposition. LeEXP2 preferentially bound to cellulose over lignin, and the binding capability to given substrates was not related to the crystallinity. This is the first study to characterize the functional role of LeEXP2 in cellulose degradation.

Synthesis, characterization, biological and catalytic applications of transition metal complexes derived from Schiff base

A novel series of Cu(II), Ni(II), Zn(II), Co(II), and Cd(II) complexes have been synthesized from the Schiff base. Structural features were determined by analytical and spectral techniques like IR, (1)H NMR, UV-vis, elemental analysis, molar electric conductibility, magnetic susceptibility and thermal studies. The complexes are found to be soluble in dimethylformamide and dimethylsulfoxide. Molar conductance values in dimethylformamide indicate the non-electrolytic nature of the complexes. Binding of synthesized complexes with calf thymus DNA (CT DNA) was studied. There is significant binding of DNA in lanes 2, 3, and 5. Lanes 4 and 6 are showing more florescence when compared to the control indicating that these molecules are strongly bound to the DNA by inserting themselves between the two stacked base pairs and exhibiting their original property of fluorescence. Angiogenesis study has revealed that the compounds B-2, B-4 and B-5 have potent antitumor efficacy and activation of antiangiogenesis could be one of the possible underlying mechanisms of tumor inhibition.

Morphological and pharmacological investigation on some biopotent materials derived from substituted pyrimidine and imidazole enzyme constituents

Coordinating behavior of novel N2O type mixed ligand complexes (1-6) have been synthesized from substituted fluoropyrimidine [5-Fluorouracil (5-FU; A)] with biopotent imidazole enzyme constituents (B) viz., imidazole(him) and benzimidazole(bim) in the presence of Ni(II), Cu(II) and Zn(II) ions. Synthesized complexes were characterized by chemical analysis, spectral studies, magnetic moment and conductivity measurements. The results of chemical analysis and the observed low molar conductance values propose their stoichiometry to be 1:1:1 (M:A:B) with non-electrolytic nature. From the spectral data, it is inferred that the ligands A & B coordinate with M(II) ions in bi and monodentate approach through C(4)=O, N(3) and imidazole ring N(3) atoms respectively. The thermogravimetric analysis shows the dehydration, decomposition and thermal stability of mixed ligand complexes. XRD and SEM patterns show sharp crystalline peaks with homogeneous morphology. In vitro antimicrobial activities of free ligands (A & B) and their metal complexes were screened against some pathogenic strains by well diffusion technique. Absorption and gel electrophoresis experiments on the interaction of mixed ligand complexes with DNA suggest that all the complexes can bind as well as cleave the DNA by intercalation between chromophores and DNA base pairs. In addition, in vitro antioxidant activities were tested by DPPH free radical scavenging model.

Interaction of firefly luciferase and silver nanoparticles and its impact on enzyme activity

We report on the dose-dependent inhibition of firefly luciferase activity induced by exposure of the enzyme to 20 nm citrate-coated silver nanoparticles (AgNPs). The inhibition mechanism was examined by characterizing the physicochemical properties and biophysical interactions of the enzyme and the AgNPs. Consistently, binding of the enzyme induced an increase in zeta potential from -22 to 6 mV for the AgNPs, triggered a red-shift of 44 nm in the absorbance peak of the AgNPs, and rendered a 'protein corona' of 20 nm in thickness on the nanoparticle surfaces. However, the secondary structures of the enzyme were only marginally affected upon formation of the protein corona, as verified by circular dichroism spectroscopy measurement and multiscale discrete molecular dynamics simulations. Rather, inductively coupled plasma mass spectrometry measurement revealed a significant ion release from the AgNPs. The released silver ions could readily react with the cysteine residues and N-groups of the enzyme to alter the physicochemical environment of their neighboring catalytic site and subsequently impair the enzymatic activity.