Presence Of Zinc Research Articles

Novel mono- and dinucleating ligands-containing artificial di- and tetrahistidine and their zinc(II) complexes as a structural phosphotriesterase models for the hydrolysis of p-nitrophenyl diphenylphosphate (p-NPDPP)

Two new artificial peptides with histidine side chains, namely N-methyl N,N′-bis(Im-bzl-l-histidylmethylestermethyl)amine L1 and N,N′,N″,N‴-tetrakis(Im-bzl-l-histidylmethyl-estermethyl)ethylene diamine L2 have been synthesized and were shown to form stable zinc complexes [L1Zn(H2O)2](ClO4)2 1 and [L2Zn2(H2O)3](ClO4)4 2, respectively. Solution studies (pH–1NMR titrations) of the ligand L2 in the presence of zinc ions were also reported. The catalytic activity of zinc complex species 1 and 2 as structural phosphotriestrase models were tested on the hydrolysis/detoxification of p-nitrohenl diphenylphosphate (p-NPDPP). From the correlation between the pH-rate profiles and the species distribution curves, the catalytically active species could be identified. On the basis of R-dependence as well as the rate acceleration of each complex, the possibility of cooperative action of zincs in dinuclear zinc complex is debated.

Utilization of Kynurenic Acid Produced from D-kynurenine in an in Vitro Assay of D-Amino Acid Oxidase Activity

D-2-Amino-4-(2-aminophenyl)-4-oxobutanoic acid (D-kynurenine) was used to assay D-amino acid oxidase (DAAO, EC 1.4.3.3) activity. D-Kynurenine is enzymatically converted by DAAO to 4-hydroxyquinoline-2-carboxylic acid (kynurenic acid), which emits fluorescence at 398 nm (excitation wavelength 251 nm) in the presence of zinc ions. Using D-kynurenine as a substrate, fluorescence intensity originating from kynurenic acid can be used to assess DAAO activity. Under enzymatic reaction at pH 8.5 (37°C), the Km and Vmax of D-kynurenine were 148 μM and 5.53 μmol/min per mg, respectively. Inhibition of DAAO by a commercial DAAO inhibitor was clearly observed in this assay.

Zinc-dependent effects of small molecules on the insulin-sensitive transcription factor FOXO1a and gluconeogenic genes

Metal-binding compounds have recently been reported to have anti-hyperglycaemic properties in vivo. In the current study, we have investigated the ability of these compounds and related structures to induce insulin-like signal transduction to downstream effectors such as the transcription factor FOXO1a and the key gluconeogenic regulatory enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6-phosphatase (G6Pase). Our results indicate that β-thujaplicin, diethyldithiocarbamate (DEDTC) and its clinically-used dimer disulfiram, induce insulin-like dose-dependent effects on signalling to FOXO1a in a manner that is strictly dependent on the presence of zinc ions, as other ions including aluminium, cobalt, copper, lithium and manganese cannot substitute. The most potent compound tested on gluconeogenesis is disulfiram, which in the presence of 10 μM zinc, inhibited both PEPCK and G6Pase with an IC50 of 4 μM. Our results demonstrate that metal-binding compounds with diverse structures can induce zinc-dependent insulin-like effects on signal transduction and gene expression.

Zinc Oxide Nanorods Prepared in Mixed Solvents

In this paper, we demonstrate a novel and direct synthesis of hexagonal-shaped zinc oxide (ZnO) nanorods at very low temperature of ~ 80oC simply by using metallic zinc foil and de-ionized (DI) water with few drops of ethanol. The formation of ZnO structures by the reaction of metals with DI water is suggested to occur due to the oxidation of metallic zinc in presence of water. The synthesized ZnO products were characterized in terms of their structural and optical properties. By the morphological investigations using FESEM, it was observed that the grown products are hexagonal-shaped ZnO nanorods with the diameters in the range of 50-60 nm and length with ~ 1 micrometer. The EDS and XRD pattern confirmed the composition and crystallinity of the grown nanorods and revealed that the grown products are pure ZnO with the wurtzite hexagonal phase.

Molecular recognition of uracil and adenine nucleobases by Langmuir monolayers of metal complexes of amphiphilic cyclen

The molecular recognition of purine and pyrimidine nucleobases (adenine and uracil) by the Langmuir monolayers of amphiphilic macrocyclic tetraamine (dicetylcyclen) is studied using independent methods of quartz microbalance and FTIR spectroscopy. Data show that the specific binding of pyrimidine base occurs in the presence of zinc ions and results from the formation of macrocyclic complex with metal ion followed by the coordination of uracil imide group to the metal complex. Experimental conditions that favor an increase in the efficiency of the recognition of uracil by the monolayer of metal complexes are determined. The inhibition effect of trace amounts of copper ions in the subphase containing zinc chloride-uracil mixture on the uracil recognition by the monolayer of dicetylcyclen is revealed. It is also established that the monolayer of Zn2+-dicetylcyclen complexes is inactive with respect to purine base (adenine). Therefore, the results suggest that monolayers of amphiphilic cyclen can be used as planar biomimetic modeling the function of active sites of transcription metalloproteins.

Effects of coumarin substituents on the photophysical properties of newly synthesised phthalocyanine derivatives

In this study, synthesis of new ligands, 8-hydroxy-3-[p-(3′,4′-dicyanophenoxy)-phenyl]coumarin and 8-hexyloxy-3-[p-(3′,4′-dicyanophenoxy)-phenyl]coumarin, and their phthalocyanines, 2,9,16,23-tetrakis[8-hexyloxy-3-(4-oxyphenyl)coumarin]-metal-free and metallophthalocyanines {M[Pc(OBzCou)4] (M = 2H, Zn(II), Co(II); Bz: benzene; Cou: coumarin)} were synthesised. The novel chromogenic compounds were characterised by elemental analysis: 1H NMR, 13C NMR, MALDI-TOF, IR and UV–vis spectral data. The effect of coumarin substituents on the photophysical properties of metal-free (H2Pc) and zinc phthalocyanines (ZnPc) derivatives has been examined. Spectrophotometric measurements revealed that coumarin-substituted ZnPc derivatives were in the unaggregated form, whereas those of H2Pc species were in aggregated form. It means that substitution of coumarin derivative prevents the cluster formation in the presence of zinc ion in the centre of Pc.

Zinc Surfactant Effects on Improved Mechanical Properties of Silica-Filled Silicone Rubber/Natural Rubber Blends Using TESPD Coupling Agent

Abstract Zinc surfactant (ZS) is added into natural rubber (NR)/silica/TESPD (bis (triethoxysilyl propyl) disulfide) and silicone rubber (SR)/NR/silica/TESPD compounds and these compounds are vulcanized. The addition of the ZS shows significant improvements on mechanical properties on both compounds. It increases the torque maximum values of the compounds as well as the tan values, which is an indirect implication that the vibration isolation property is increased. It shows the presence of zinc ion in the ZS helps silane coupling with double bond in the rubber chain. This results in improved mechanical properties such as the modulus, tensile strength, elongation at break, and hardness.

Relative Humidity Sensing Studies of WO<sub>3</sub>-ZnO Nanocomposite

Paper reports morphological and humidity sensing studies of WO3 and WO3-ZnO nanocomposite pellets prepared in the weight % ratio of 10:1, 4:1 and 2:1 by solid-state reaction route. The pellets have been annealed at temperatures of 300-500°C. XRD pattern shows peaks of ZnWO4 formed due to solid state reaction between WO3 and ZnO. SEM micrographs show that the sensing elements manifest porous structure. Granulation and tendency to agglomerate seen in the SEM micrograph are due to the presence of zinc ions in ZnWO4. Nanoparticles are having their sizes in the range 37-182 nm. The average Kelvin radius at 20°C room temperature is 27 Ả. Humidity sensing application of the pellets has been studied in a humidity control cabinet. It is observed that as relative humidity increases, there is decrease in the resistance of pellets in the range 10-85% RH. Sensing element of WO3-ZnO in 2:1 weight % ratio shows best results in 10-85 % relative humidity range. The average sensitivity of this sample is 1.20 MΩ/%RH. This sensing element shows good reproducibility, low hysteresis and less effect of aging.

Synthesis of Prostaglandin E1 Phosphate Derivatives and Their Encapsulation in Biodegradable Nanoparticles

Prostaglandin E(1) (PGE(1)) is an effective treatment for peripheral vascular diseases. The encapsulation of PGE(1) in nanoparticles for its sustained-release would improve its therapeutic effect and quality of life (QOL) of patients. In order to encapsulate PGE(1) in nanoparticles prepared with a poly(lactide) homopolymer (PLA) and monomethoxy poly(ethyleneglycol)-PLA block copolymer (PEG-PLA), we synthesized a series of PGE(1) phosphate derivatives and tested their efficacy. Among them, PGE(1) 2-(phosphonooxy)ethyl ester sodium salt (C2) showed the most efficient hydrolysis to yield PGE(1) in human serum. An in vitro platelet aggregation assay showed that C2 inhibited aggregation only after pre-incubation in serum, suggesting that C2 is a prodrug of PGE(1). In vivo, intravenous administration of C2 caused increase in cutaneous blood flow. In the presence of zinc ions, all of the synthesized PGE(1) phosphate derivatives could be encapsulated in PLA-nanoparticles. Use of L-PLA instead of D,L-PLA, and high molecular weight PLA resulted in a slower release of C2 from the nanoparticles. We consider that C2-encapsulated nanoparticles prepared with L-PLA and PEG-D,L-PLA have good sustained-release profile of PGE(1), which is useful clinically.

Eosin as Corrosion Inhibitor for Carbon Steel in Well Water

The inhibition efficiency of Eosin in controlling corrosion of carbon steel immersed in well water, has been evaluated by mass loss method both in absence and presence of zinc ion. A synergistic effect exists between Eosin (EN) and Zn 2+ . The inhibition efficiency (IE) of the EN - Zn 2+ system decreases with increase in immersion period. Addition of N-cetyl-N,N,N-trimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS), sodium sulphite (Na2SO3) does not change the excellent inhibition efficiency of the EN-Zn 2+ system. Polarization study suggests that the EN-Zn 2+ system functions as an anodic inhibitor system. AC impedance spectra reveal the presence of a protective film on the metal sur- face. FTIR spectra indicate that the protective film consists of Fe 2+ - EN complex and Zn(OH)2.

Active-site architecture and catalytic mechanism of the lipid A deacylase LpxR of Salmonella typhimurium

The lipid A portion of lipopolysaccharide, the major component of the outer leaflet of the outer membrane of gram-negative bacteria, is toxic to humans. Modification of lipid A by enzymes often reduces its toxicity. The outer-membrane protein LpxR from Salmonella typhimurium is a lipid A-modifying enzyme. It removes the 3'-acyloxyacyl moiety of the lipid A portion of lipopolysaccharide in a Ca(2+)-dependent manner. Here, we present the crystal structure of S. typhimurium LpxR, crystallized in the presence of zinc ions. The structure, a 12-stranded beta-barrel, reveals that the active site is located between the barrel wall and an alpha-helix formed by an extracellular loop. Based on site-directed mutagenesis and modeling of a substrate on the active site, we propose a catalytic mechanism similar to that of phospholipase A2, in which a Ca(2+) forms the oxyanion hole and a histidine activates a water molecule (or a cascade of two water molecules) that subsequently attacks the carbonyl oxygen of the scissile bond.

Bisquinoline-based fluorescent zinc sensors

Several bisquinoline derivatives, N,N'-bis(2-quinolylmethyl)-N,N'-dialkylethylnediamines (alkyl=methyl, ethyl, isopropyl and t-butyl), have been synthesized and their fluorescent responses toward zinc ion were investigated. These compounds exhibit zinc ion-induced fluorescence and their intensities decrease as the alkyl groups become larger. The t-butyl derivative (BQDtBEN) exhibited negligible fluorescence even in the presence of zinc ion. The fluorescence intensity of the zinc complex of the bisquinoline derivative (BQDMEN) is higher than that of TQEN (N,N,N',N'-tetrakis(2-quinolylmethyl)ethylenediamine), indicating that the TQEN-Zn complex has an intramolecular quenching mechanism due to the energy transfer among four quinoline rings and the remaining photoinduced electron transfer (PET) mechanism. Introduction of methoxy substituents into the quinoline ring shifted the excitation and emission wavelengths towards a lower-energy direction and increased the fluorescence intensity, which allows N,N'-bis(6-methoxy-2-quinolylmethyl)-N,N'-dimethylethylenediamine (6-MeOBQDMEN) to be used for cellular fluorescent microscopic analysis (lambdaex=331 nm, lambdaem=406 nm and phi=0.28 for 6-MeOBQDMEN-Zn complex).

Regulation of UMSBP activities through redox-sensitive protein domains

UMSBP is a CCHC-type zinc finger protein, which functions during replication initiation of kinetoplast DNA minicircles and the segregation of kinetoplast DNA networks. Interactions of UMSBP with origin sequences, as well as the protein oligomerization, are affected by its redox state. Reduction yields UMSBP monomers and activates its binding to DNA, while oxidation drives UMSBP oligomerization and impairs its DNA-binding activity. Kinetics analyses of UMSBP–DNA interactions revealed that redox affects the association of free UMSBP with the DNA, but has little effect on its dissociation from the nucleoprotein complex. A previously proposed model, suggesting that binding of DNA is regulated via the reversible interconversions of active UMSBP monomers and inactive oligomers, was challenged here, revealing that the two redox-driven processes are not interrelated. No correlation could be observed between DNA-binding inhibition and UMSBP oligomerization, upon oxidation of UMSBP. Moreover, while the presence of zinc ions was found to be essential for the interaction of UMSBP with DNA, UMSBP oligomerization occurred through zinc-depleted, unfolded zinc finger domains. Site directed mutagenesis analysis of UMSBP suggested that its unique methionine residue, which can be oxidized into methionine sulfoxide, is not involved in the redox-mediated regulation of UMSBP–DNA interactions.

Photo-and thermochromic spiranes 31.* Structure and photochromic properties of functionalized benzoxazine spiropyrans

An X-ray diffraction study gave the structure of a 4-oxohydro-2H-1,3-benzoxazine spiropyran with molecular formula C28H25N3O7, in which the π-electron-withdrawing formyl group is replaced with a chelatophoric hydrazine fragment containing a methoxy group. The structural parameters of this spiropyran were determined and compared with the data for similar spiropyrans. The photochromic properties of this compound in acetonitrile were studied in the presence of zinc ions.

Metal-triggered changes in the stability and secondary structure of a tetrameric dihydropyrimidinase: A biophysical characterization

Dihydropyrimidinase is involved in the reductive pathway of pyrimidine degradation, catalysing the reversible hydrolysis of the cyclic amide bond (–CO–NH–) of 5,6-dihydrouracil and 5,6-dihydrothymine to the corresponding N-carbamoyl-β-amino acids. This enzyme is an attractive candidate for commercial production of D-amino acids, which are used in the production of semi-synthetic β-lactams, antiviral agents, artificial sweeteners, peptide hormones and pesticides. We have obtained the crystal structure of the dihydropyrimidinase from Sinorhizobium meliloti (SmelDhp) in the presence of zinc ions, but we have not been able to obtain good diffracting crystals in its absence. Then, the role of the ion in the structure of the protein, and in its stability, remains to be elucidated. In this work, the stability and the structure of SmelDhp have been studied in the absence and in the presence of zinc. In its absence, the protein acquired a tetrameric functional structure at pH ∼ 6.0, which is stable up to pH ∼ 9.0, as concluded from fluorescence and CD. Chemical-denaturation occurred via a monomeric intermediate with non-native structure. The addition of zinc caused: (i) an increase of the helical structure, and changes in the environment of aromatic residues; and, (ii) a higher thermal stability. However, chemical-denaturation still occurred through a monomeric intermediate. This is the first hydantoinase whose changes in the stability and in the secondary structure upon addition of zinc are described and explained, and one of the few examples where the zinc exclusively alters the secondary helical structure and the environment of some aromatic residues in the protein, leaving unchanged the quaternary structure.

Tripeptide-modified silicon nanowire based field-effect transistors as real-time copper ion sensors

A highly sensitive and specific copper ion sensor using single crystalline silicon nanowires (SiNWs) configured as field-effect transistors (FETs) is reported. The surface of SiNWs is functionalized with a His-containing tripeptide which serves as a copper sensitive layer. It is found that the complexation between copper ions and His-containing tripeptides leads to an increase in the SiNW conductance, and the position of His residue in the tripeptide plays an important role for the binding of copper ions. Only Gly-Gly-His-modified SiNWs exhibit selectivity for copper ions in the presence of zinc ions whereas Gly-His-Gly-modified SiNWs do not. Our experimental results demonstrate the potential utility of oligopeptide-modified SiNWs as metal ion sensors.

The zinc-binding protein Hot13 promotes oxidation of the mitochondrial import receptor Mia40.

A disulphide relay system mediates the import of cysteine-containing proteins into the intermembrane space of mitochondria. This system consists of two essential proteins, Mia40 and Erv1, which bind to newly imported proteins by disulphide transfer. A third component, Hot13, was proposed to be important in the biogenesis of cysteine-rich proteins of the intermembrane space, but the molecular function of Hot13 remained unclear. Here, we show that Hot13, a conserved zinc-binding protein, interacts functionally and physically with the import receptor Mia40. It improves the Erv1-dependent oxidation of Mia40 both in vivo and in vitro. As a consequence, in mutants lacking Hot13, the import of substrates of Mia40 is impaired, particularly in the presence of zinc ions. In mitochondria as well as in vitro, Hot13 can be functionally replaced by zinc-binding chelators. We propose that Hot13 maintains Mia40 in a zinc-free state, thereby facilitating its efficient oxidation by Erv1.

Folding Induced Assembly of Polypeptide Decorated Gold Nanoparticles

Reversible assembly of gold nanoparticles controlled by the homodimerization and folding of an immobilized de novo designed synthetic polypeptide is described. In solution at neutral pH, the polypeptide folds into a helix-loop-helix four-helix bundle in the presence of zinc ions. When immobilized on gold nanoparticles, the addition of zinc ions induces dimerization and folding between peptide monomers located on separate particles, resulting in rapid particle aggregation. The particles can be completely redispersed by removal of the zinc ions from the peptide upon addition of EDTA. Calcium ions, which do not induce folding in solution, have no effect on the stability of the peptide decorated particles. The contribution from folding on particle assembly was further determined utilizing a reference peptide with the same primary sequence but containing both D and L amino acids. Particles functionalized with the reference peptide do not aggregate, as the peptides are unable to fold. The two peptides, linked to the nanoparticle surface via a cysteine residue located in the loop region, form submonolayers on planar gold with comparable properties regarding surface density, orientation, and ability to interact with zinc ions. These results demonstrate that nanoparticle assembly can be induced, controlled, and to some extent tuned, by exploiting specific molecular interactions involved in polypeptide folding.

Antiatherogenic effects of zinc are associated with copper in iron-overloaded hypercholesterolemic rabbits

Fifty-four juvenile male New Zealand white rabbits were randomly allocated to 9 groups including chow-fed rabbits without mineral supplementation, HC diet fed rabbits without mineral supplementation, HC + Cu, HC + Zn, HC + FeO, HC + Cu + Zn, HC + FeO + Cu, HC + FeO + Zn, and HC + FeO + Cu + Zn. Feeding HC diet resulted in a significant (P < .001) increase in the serum cholesterol, TG, LDL, and very LDL except HDL when compared with chow-fed rabbits. The highest serum lipid profiles were observed in the FeO rabbits without copper or zinc supplementation. A modest decrease in serum thiobarbituric acid reactant substances in rabbits given the HC + Zn was accompanied by a significant (P < .05) increase in antioxidant enzymes activities excluding superoxide dismutase that was markedly lower than those given the HC + Cu (12.83 +/- 2.13 vs 16.00 +/- 2.23 U/mL serum). Supplementation with copper alone in both the FeO and the non-FeO rabbits significantly (P < .001) enhanced serum ceruloplasmin activity in comparison with other groups, but co-supplementation of copper plus zinc in the non-FeO rabbits did not significantly (P > .05) affect ceruloplasmin activity in comparison with those treated with unsupplemented regimens. A significant decrease was found in sudanophilia area of rabbits supplemented with zinc (62.36% +/- 3.55%) compared to those given the HC + FeO, the HC + FeO + Cu, and HC without mineral supplementation; however, no significant (P > .05) difference in animals given the HC + Cu, the HC + Cu + Zn, and the HC + FeO + Zn was observed. Based on these findings, it may be suggested that the antiatherogenic effects of zinc in presence of copper, on which there is overloading of iron, is reduced under hypercholesterolemia.

Hydration study of ordinary portland cement in the presence of zinc ions

Hydration products of Portland cement pastes, hydrated in water and in the presence of zinc ions were studied comparatively at different ages. Hydration products were studied by X ray diffractions (XRD) and infrared spectroscopy (IR). Although IR is not frequently used in cement chemistry, it evidenced a new phase Ca(Zn(OH)3)2. 2H2O formed during cement hydration in the presence of zinc. The significant retardation of early cement hydration in the presence of zinc is assessed in detail by differential calorimetry as a complement to the study carried out by IR and XRD, providing evidence that permits to evaluate the kinetic of the early hydration.