Presence Of Certain Metal Ions Research Articles

Multiresponse optimization in amylolytic desizing of viscose fabric in the copresence of ferrous ions and an anionic surfactant

Purpose This study aims to investigate the effect of the copresence of ferrous (Fe2+) ions and sodium dodecyl sulfate (SDS) on the activity of an amylase enzyme during the desizing of greige viscose fabric for potential industrial applications. The removal of starches is an essential step before processing the fabric for dyeing and finishing operations. The authors tend to accomplish it in eco-friendly and sustainable ways. Design/methodology/approach The experiments were designed under the Taguchi approach, and the results were analyzed using grey relational analysis to optimize the process. The textile properties of absorbency, reducing sugars, bending length, weight loss, Tegawa rating and tensile strength were assessed using the standard protocols. The control and optimized viscose specimens were investigated for certain surface chemical properties using advanced analytical techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). Findings The results demonstrate that the Fe2+ concentration and process time were the main influencing factors in the amylolytic desizing of viscose fabric. The optimized process conditions were found to be 0.1 mm Fe2+ ions, 3 mm SDS, 80°C, 7 pH and 30 min process time. The copresence of Fe2+ ions and SDS promoted the biodesizing of viscose fabric. The SEM, Fourier transform infrared spectroscopy, XRD and TGA results demonstrated that the sizing agent has efficiently been removed from the fabric surface. Practical implications The amylase desizing of viscose fabric in the presence of certain metal ions and surfactants is a significant subject as the enzyme may face them due to their prevalence in the water systems. This could also support the biodesizing and bioscouring operations to be done in one bath, thus making the textile pretreatment process both economical and environmentally sustainable. Originality/value The authors found no report on the biodesizing of viscose fabric in the copresence of Fe2+ ions and the SDS surfactant under statistical multiresponse optimization. The biodesized viscose fabric has been investigated using both conventional and analytical approaches.

The influence of common metal ions on the interactions of the isoflavone genistein with bovine serum albumin

The interaction of genistein with bovine serum albumin (BSA) has been characterized via UV–vis, fluorescence spectroscopy and Circular Dichroism (CD) measurements under physiological conditions. In this study, we have investigated the effect of some common metal ions on the binding of genistein with BSA using fluorescence studies. The fluorescence data reveal that the binding affinity of genistein to BSA increases in presence of certain metal ions. The possibility of non-radiative energy transition from the donor tryptophan to the acceptor genistein has been observed in absence and presence of metal ions. The observed similarities in the values of efficiency of energy transfer (E) and the separation between the donor and acceptor (r) in both the cases may be correlated with the complexation between the genistein and metal ions, which is also observed from the UV–vis studies. The changes in enthalpy (ΔH°) and entropy (ΔS°) of the interaction were found to be −14.64kJmol−1 and +42.75Jmol−1K−1 respectively. These values indicate the involvement of electrostatic interactions along with a hydrophobic association that results in a positive entropy change. CD analysis shows that there is a slight increase in the% α-helical content of BSA on binding with genistein at lower molar ratios. Warfarin and ibuprofen displacement studies in accordance with the molecular docking show that genistein binds to site I (subdomain IIA) of BSA.

Inclusion of Tetrachloroquinone and Metal Ions in a Macrotricyclic Molecule with a Tetrathiafulvalene Moiety Prompts Intermolecular Electron Transfer

And here′s your host: The synthesis and characterization of triptycene-based cylindrical macrotricyclic molecule 1, which contains one tetrathiafulvalene (TTF) unit and four glycol chains, is reported. Absorption and ESR spectroscopic studies show that intermolecular electron transfer occurs from the TTF unit in 1 to a tetrachloroquinone guest in the presence of metal ions. A triptycene-based cylindrical macrotricyclic molecule 1, which contains one tetrathiafulvalene (TTF) unit and four glycol chains, is reported. Both absorption and ESR spectroscopic studies clearly indicate that intermolecular electron transfer occurs from TTF in 1 to tetrachloroquinone in the presence of certain metal ions (e.g. Sc3+, Pb2+, and Zn2+). Based on comparative studies with 3 and 5, the close intermolecular alignment between 1 and tetrachloroquinone is proposed to occur by the synergic coordination of metal ions with oxygen atoms of the glycol chains and tetrachloroquinone (as well as the sulfur atoms of TTF). The intermolecular electron transfer is facilitated by the positive shift of the reduction potentials of tetrachloroquinone through coordination with metal ions, and the close alignment of 1 and tetrachloroquinone, which is beneficial for stabilizing the electron-transfer state. 1 Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Calix[4]arene based molecular sensors with pyrene as fluoregenic unit: Effect of solvent in ion selectivity and colorimetric detection of fluoride

Fluorescent molecular sensors having excimer emission property have been designed and synthesised incorporating calix[4]arene derivatives in cone and 1,3-alternate conformation as ionophore and two pyrene moieties at close proximity as fluorophore. They exhibit strong excimer emission around 515 nm, which is used to monitor interaction of metal ions with the ionophores. Ion-binding study of these fluoroionophore has been investigated in acetonitrile–chloroform and THF–H 2O with a wide range of cations and anions and the recognition process is monitored by luminescence, UV–Vis and 1H NMR (for F −) spectral changes. The present study demonstrated profound influence of solvent in ion selectivity, in acetonitrile–chloroform they formed complexes with Hg 2+, Pb 2+, Cu 2+ and Ni 2+, whereas in THF–H 2O they exhibit selectivity only for Cu 2+. In the case of anions, selectivity for only F − with color change is observed. Composition of the complexes formed was determined from mass spectrometry and the binding constants were determined from fluorescence titration data. The reasons for formation of excimer emission, quenching of it in presence of certain metal ions, role of solvent in selectivity and energy/electron transfer process involved in the ion-recognition event have been discussed on the basis of experimental data.

Spectrophotometric detection of lead(II) ion using unimolecular peroxidase-like deoxyribozyme

Deoxyribonucleic acid (DNA) can form G-quadruplexes in the presence of certain metal ions. These play a functional role in a variety of biological process. A DNA 17-mer (PW17) was previously reported to bind hemin in the presence of excess potassium ion. The resulting stabilized G-quadruplex-hemin complex exhibits peroxidase-like activity. However, this activity is lost in the presence of one equivalent of Pb2+ ion. We exploit this property in a method for spectrophotometric detection of Pb2+. Inhibition by Pb2+ ion is reflected by a change in the Soret band of hemin and a sharp reduction in the catalytic activity towards hydrogen peroxide-mediated chromogenic oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate. The new method enables Pb2+ to be detected in the concentration range from 0.05 to 1.2 μM, with a detection limit of 27 nM. The assay shows high selectivity over other metal ions. It was successfully used to determine Pb2+ in water samples.

Characterization of an unusual folding pattern in a catalytically active guanine quadruplex structure

In the presence of certain metal ions, DNA and RNA can form guanine quadruplex structures, which have been proposed to play a functional role in a variety of biological processes. An 18-nucleotide DNA oligomer, PS2.M, d(GTG3TAG3CG3T2G2), was previously reported to bind hemin and the resulting complex exhibited peroxidase activity. It was proposed that PS2.M folds unimolecularly into an antiparallel quadruplex with unusual, single-base loops and terminal guanines positioned in adjacent quartets. Here we describe structural and stability properties of PS2.M alone in different buffers and metal ions, using gel electrophoresis, circular dichroism (CD), ultraviolet (UV)-visible spectroscopies, and one-dimensional 1H nuclear magnetic resonance (NMR). Native gel behavior of PS2.M in the presence of either Na+ or Pb2+ suggests the formation of unimolecular structures but, in the presence of K+, both unimolecular and multistranded structures are observed. In the presence of Pb2+ ions, PS2.M forms a unimolecular quadruplex containing three guanine quartets. CD titrations reveal that binding of Pb2+ ions to PS2.M is stoichiometric, and a single lead cation suffices to fully fold PS2.M. The PS2.M-Na+ system also forms a similar unimolecular quadruplex. In the presence of K+, the PS2.M-K+ system forms mixed species. With increasing time and PS2.M concentration, the contribution of unimolecular species decreases while that of multimolecular species increases, and this behavior is independent of buffer media. These results suggest that the catalytically active form, studied in the presence of K+, may be a parallel, multistranded quadruplex rather than an antiparallel, unimolecular quadruplex.

Gamma and ultraviolet radiation cause DNA crosslinking in the presence of metal ions at high pH.

M-DNA is a novel duplex conformation in which metal ions such as Co2+, Ni2+ or Zn2+ replace the imino protons of every base pair. An ethidium fluorescence assay was used to estimate lesions in M-DNA induced by gamma- and UV radiation. General damage to DNA was assessed from the loss of ethidium fluorescence after irradiation of calf thymus DNA. Crosslinks were measured from the return of ethidium fluorescence after a heating and cooling step. Strand breaks were estimated from the loss of fluorescence in covalently closed circular plasmid DNA after a heating and cooling step. For the Co2+ form of M-DNA, gamma-radiation caused the very efficient formation of crosslinks which was not observed with B-DNA nor with the Ni2+ or Zn2+ forms of M-DNA. The crosslinks occurred in both A-T and G-C base pairs but did not form in the presence of a free radical scavenger. Crosslinks induced by UV radiation also formed at a faster rate in the Co2+, Ni2+ and Zn2+ forms of M-DNA compared to B-DNA; crosslinking occurred in all DNA but was more prominent in AT-rich sequences and was not inhibited by a free radical scavenger. Therefore, the presence of certain metal ions may lead to large increases in the formation of radiation-induced crosslinks in DNA.

Enantioselective Complexation of Amino Acids by 6A-Deoxy-6A-hydroxyethylamino-β-Cyclodextr in and its Metallo-Derivatives in Aqueous Solution

Enantioselectivity towards several amino acids by metallo-6A-deoxy-6A-hydroxyethyl-amino-β-cyclodextrins (metallo-βCDea's) was investigated by potentiometric titration of the various amino acid/metallo-βCDea systems with NaOH solution. It was shown that the cyclodextrin derivative is capable of distinguishing between enantiomers of amino acid species in the presence of certain metal ions (Co2+, Ni2+, Cu2+and Zn2+). Ni2+-βCDea complexes show the most enantioselectivity, whereas for Cu2+- and Co2+-βCDea complexes less selectivity is observed. As expected, Zn2+-βCDea complexes exhibit no enantioselectivity. Stability and selectivity, however, do not go hand in hand, since the most stable complexes are formed with Cu2+. Several factors play a role in determining stability and selectivity in binary and ternary complexes and further study is required to gain a more comprehensive understanding of these.

Effects of pH and Metals on the Surface Tension of Aqueous Humic Materials

Humic substances play an important role in the transport and fate of xenobiotic materials in the environment. Since most of the relevant interactions take place in aqueous media, it is of prime importance to understand the behavior of these natural polymers in solution. In this study, surface tension measurements were used to elucidate conformational and structural changes in dissolved humic and fulvic acids under different conditions of pH, ionic strength, and the presence of certain metal ions. The measurements showed that the amphiphilic character of the humic solutes, which determines their surface activity, varied significantly with pH and metal content. The charge of the metal ion added was found to have an important effect in rendering the humic material sufficiently amphiphilic to migrate to the surface. As cation concentrations were increased, the formation of micelle‐like humic structures led to the restoration of higher surface tensions. Measurements with materials of different molecular size indicated that these structures could arise from both intermolecular aggregation and intramolecular coiling. Kinetic measurements showed that the evolution of surface tension values in humic acid solutions followed a course that was consistent with the migration of metal ions within the humic structure. This is thought to involve the formation and subsequent disintegration of hydrophobic domains as the metal–humate interactions change during a period of hours.

ATP and Mg2+ Ions Regulate Both Conformation and Aminoacylation Capacity of Transfer RNA.

It has been known that transfer RNA assumes a functional conformation in the presence of certain metal ions, most commonly magnesium ions. Several Mg2+-binding sites of high affinity have been revealed by X-ray crystallographic analyses of yeast tRNAPhe. On the other hand, ATP, a naturally occurring high-energy compound and which is one of the substrates in aminoacylation of tRNA, is known to have ability to chelate Mg2+. We therefore examined the possibility that the conformation of tRNA is regulated by the quantitative balance between Mg2+ and ATP, and consequently biological activity of tRNA is modulated as well. Structural transition of tRNA was monitored by measuring the melting profiles of yeast tRNATyr in the presence of Mg2+ and/or ATP at various [ATP]/[Mg2+] ratios. Tyrosine-accepting activity of yeast tRNATyr was also measured under the similar solution conditions. These results clearly indicated that conformation of tRNA and its aminoacylation capacity can be easily modulated by changing the relative concentration ratio of Mg2+ and ATP.

Central non-Pur.Pyr sequences in oligo(dG.dC) tracts and metal ions influence the formation of intramolecular DNA triplex isomers.

The effect of the central non-Pur.Pyr sequences in oligo(dG.dC) inserts on determining the type of intramolecular DNA triplex isomers formed in negatively supercoiled plasmids was investigated. Different triplex types (H-r3, H-r5, and H-y3), revealed by a combination of chemical probing and Maxam-Gilbert sequencing reactions, were adopted by the oligo(dG.dC) tracts depending on the length and composition of the central non-Pur.Pyr sequences (0, 3, or 5 base pairs) and the kind of metal ions. The H-r3 triplex conformer, one isomer of a Pur.Pur.Pyr structure, was formed in the (C)20 and (C)10GCG(C)10 inserts in plasmids in the presence of certain metal ions. Interestingly, H-r5, the other isomer of the Pur.Pur-Pyr triplex which had not been detected previously, was formed in a (C)9GAATT(C)9 insert in the presence of either Mg2+ or Ca2+. Alternatively, H-y3, one isomer of a Pyr.Pur.Pyr triplex, was formed in the (C)9GAATT(C)9 insert in the absence of metal ions. Thus, central non-Pur.Pyr sequences and metal ions play a role as determinants of the types of intramolecular triplexes formed; they also reduce the requirement of longer Pur.Pyr repeat sequences to form intramolecular triplexes. Furthermore, the effects of MgCl2 concentration and pH on the formation of triplex isomers were examined. The Pur.Pur.Pyr conformations (H-r3 and H-r5) may be the favored conformations in the cellular milieu, since they are stable at physiological pH and metal ion concentration.

Metal ions cause the isomerization of certain intramolecular triplexes.

The influence of cations on the capacity of five oligopurine.oligopyrimidine mirror repeat sequences to adopt intramolecular triplexes (the usual H-y3 isomer and/or the rare H-y5 isomer) in recombinant plasmids was investigated. Unexpectedly, the presence of certain metal ions (magnesium, zinc, manganese, and calcium) stabilized the (GAA)4TTCGC(GAA)4 insert in the rare H-y5 when cloned into either of two different sequence backgrounds. Alternatively, either shortening or lengthening the sequence at the central interruption, which becomes the loop of the triplex, led to the formation of the canonical H-y3 under all conditions tested. Similarly, other oligopurine.oligopyrimidine mirror repeat sequences (i.e. (GAA)8 or (GGA)8) formed only the H-y3 under all experimental conditions. All triplexes were stabilized by negative supercoiling at pH 5.0; chemical probe and primer extension analyses served as critical structural tools. Hence, the nature of the central interruption sequence (the loop) of the mirror repeat is important for the stabilization of the H-y5. This region may be important for metal ion binding in the initial stages of triplex formation and thus may play a critical role in determining which isomer is formed. The possible biological role of a DNA sequence adopting three different conformations is discussed.

Purification and characterization of an extracellular β-glucosidase from the rumen fungus Neocallimastix frontalis EB188

An extracellular β-glucosidase (E3.2.1.21) from the rumen fungus Neocallimastix frontalis EB188 was purified. The purification protocol included hydroxylapatite, gel filtration, and ion exchange chromatographies and native polyacrylamide gel electrophoresis. The enzyme readily hydrolysed p-nitrophenyl (pNP) β- d-glucopyranoside, and cellobiose, but not a variety of other substrates. Activity was inhibited by glucose ( K i = 10.5 m m ) and glucono-δ-lactone ( K i = 0.24 m m ). Activity was inhibited in the presence of certain metal ions and stimulated by dithiothreitol. The enzyme had a denatured molecular weight of 125,500 daltons and possessed an isoelectric focusing point of 7.10. Using pNP β- d-glucopyranoside as substrate, the K m and V max values of the enzyme were 2.5 m m and 5.02 IU mg −1, respectively. The temperature optimum of the activity was 45°C. The enzyme was rapidly inactivated at 65°C. The pH activity optimum occurred broadly between 5.5 and 7.0.

Spectrophotometric and derivative spectrophotometric determination of copper (II) with dithizone in aqueous phase

A Spectrophotometric and derivative Spectrophotometric study of Cu-dithizonate complex in aqueous phase in the presence of Triton X-100, a neutral surfactant, is reported. The system obeys Beer's law between 1.0 × 10−6−9.0 × 10−6 mol/l of Cu2+; detection limit is 12 ng/ml. The molar absorption coefficient, specific absorptivity and Sandell's sensitivity of the complex are 3.06 × 104 1 mol−1 cm−1, 0.4825 ml g−1 cm−1 and 2.1 × 10−3 μg cm−2, respectively. The conditional stability constant of the 1 ∶ 2 complex, calculated considering simultaneously existing equilibria, has been found to be 1.73 × 1011 I2 mol2 (I = 0.07, pH 1.4, temperature = 10 °C). Absorption studies in the derivative mode have been carried out to determine the absorption maximum of the complex and to overcome interference due to the presence of certain metal ions. The method has been validated by determination of copper in beers, wines, human hair, goat liver and fly ash samples.

NEW FLAVIN SEMIQUINONE RADICALS AS PRODUCED BY THE REACTION WITH NADH MODEL COMPOUNDS

Abstract The oxidation activity of a flavin (PyFl) with a fused pyridine moiety as a metal-chelation site was enhanced in the presence of certain metal ions. The reaction of PyFl and 1-benzyl-1,4-dihydronicotinamide in the presence of Mg(II), Zn(II), and Cd(II) in acetonitrile gave a transient absorption band at around 500 nm and an ESR spectrum attributable to the semiquinone radical. This is the first example for the flavin semiquinone radical produced by the reaction with an NADH model compound.

Presence of an amino acid oxidase in photosystem II of Anacystis nidulans.

Membrane fractions from the blue‐green algae Anacystis nidulans can catalyze O2 evolution with ferricyanide as acceptor in the light and the dark oxidation of l‐arginine. The two reactions are both inhibited by o‐phenanthroline, but they respond to certain trivalent, divalent and monovalent cations (like e.g. La3+ or Ca2+ or K+) in different ways. These metals stimulate the Hill reaction with ferricyanide as acceptor, but totally inhibit l‐arginine oxidation. The order of effectiveness is M3+ > M2+ > M+. The effect of e.g. Ca2+ on the dark oxidation of l‐arginine mirrors the effect of Ca2+ on the light‐driven O2 evolution with ferricyanide, as though these two activities are mutually exclusive, i.e. one process is inhibited to the extent that the other is activated. The enzyme responsible for the dark oxidation of l‐arginine has been purified from A. nidulans and shown to be a flavo‐enzyme [Pistorius, E. K. and Voss, H. (1980) Biochim. Biophys. Acta, 611, 227–240].Active photosystem II particles have also been isolated from Anacystis membrane fractions. They can catalyze 2,6‐dichloroindophenol reduction with diphenylcarbazide as donor in the light. They retain l‐arginine oxidation activity in the presence of EDTA. Both reactions are inhibited by o‐phenanthroline. Moreover, it could be shown that one of the protein bands which has been shown to be characteristic for photosystem II particles [Koenig, F. and Vernon, L. P. (1981) Z. Naturforsch. C36, 295–304], co‐chromatographs with the purified l‐amino‐acid oxidase on SDS gels. An antibody prepared to the purified l‐amino‐acid oxidase also gave a precipitin line with detergent‐treated photosystem II particles.The experiments show that the l‐amino‐acid oxidase is part of photosystem II particles in A. nidulans. This protein might have a dual role: acting as an electron transferring protein in photosynthesis in the presence of certain metal ions (M3+ > M2+ > M+) and as an l‐amino‐acid oxidase in the absence of these.

Simultaneous determination of trace concentrations of arsenic, antimony, bismuth, selenium and tellurium in aqueous solution by introduction of the gaseous hydrides into an inductively coupled plasma source for emission spectrometry. Part I. Preliminary studies

In the simultaneous determination of arsenic, antimony, bismuth, selenium and tellurium by measurement of the atomic line emission from the elements in an inductively coupled plasma source after their introduction as the gaseous hydrides, two types of possible interferences were investigated. Mutual interferences between the analytes were found to be negligible under the operating conditions used. The presence of certain metal ions in solution resulted in low recoveries of some of the analytes, especially selenium and tellurium. However, this could be overcome by prior separation of the analytes by co-precipitation on lanthanum hydroxide.

Simultaneous determination of trace concentrations of arsenic, antimony, bismuth, selenium and tellurium in aqueous solution by introduction of the gaseous hydrides into an inductively coupled plasma source for emission spectrometry. Part II. Interference studies

In the simultaneous determination of arsenic, antimony, bismuth, selenium and tellurium by measurement of the atomic line emission from the elements in an inductively coupled plasma source after their introduction as the gaseous hydrides, two types of possible interferences were investigated. Mutual interferences between the analytes were found to be negligible under the operating conditions used. The presence of certain metal ions in solution resulted in low recoveries of some of the analytes, especially selenium and tellurium. However, this could be overcome by prior separation of the analytes by co-precipitation on lanthanum hydroxide.

Progesterone-binding protein in human myometrium. Influence of metal ions on binding.

ABSTRACT Progesterone-binding protein was isolated by (NH4)2SO4 precipitation from the myometrial cytosol fraction obtained from three women treated with estrogen prior to hysterectomy. The in vitro steroid-binding process was found to be sensitive to the presence of certain metal ions. The cations seemed to interfere directly with SH groups at the progesterone binding site. The most potent inhibitor of the binding was Hg(II) (50% decrease in binding in the presence of 8 μmo1/1) followed by Cu(II) (10 μmo1/1), Ag(I) (13 μmo1/1), Zn(II) (17 μmo1/1) and Fe(II) (2.5 mmo1/1). The inhibition achieved with cupric ions was partially abolished by dithiothreitol and EDTA. Ligand-bound protein was less susceptible to the action of cations than unbound binding protein.

Studies on the Mixed-Ligand Complexes.II. Synthesis of the Mixed-Ligand Complexes between 8-Hydroxyquinoline-5-sulfonic Acidand L-Histidine with Metals

Since some of oxine-like compounds showed antibacterial action in the presence of certain metal ions, this experiment was carried out to synthesize a model compound of mixed-ligand complexes of 8-hydroxyquinoline-5-sulfonic acid (abbr. as HQS below), being a water soluble oxine derivative, L-histidine (abbr. as His) and certain metal ions. The authors reported on the synthesis of the mixed-ligand complex of Co (III) containing oxine and glycine. In this paper His was used as a chelating amino acid, which is expected to form mixed-ligand complexes more easily than in the case of glycine in cooperating with HQS, since the stability constants of His-metal complexes are much closer to those of HQS-metal complexes.