Presence Of Certain Metal Cations Research Articles

A DNA Polymerase Stop Assay for Characterization of G-Quadruplex Formation and Identification of G-Quadruplex-Interactive Compounds.

Guanine-rich DNA sequences are able to spontaneously fold into G-quadruplex structures in the presence of certain metal cations. In the human genome, the majority of DNA G-quadruplexes form at the telomeres and regulatory regions of cancer-related genes. The formation of these structures is implicated in nuclear processes involving DNA, including transcription, DNA replication, and DNA repair. In the past few decades, small molecules which can stabilize these structures have been shown to suppress the telomere extension and to inhibit oncogene transcription. Therefore, DNA G-quadruplexes are thought to be attractive targets for new anticancer therapies. In this chapter, we describe step by step a DNA polymerase extension method for the characterization of G-quadruplex formation and identification of G-quadruplex-interactive compounds. This method is based on the principle that DNA polymerase is incapable to resolve G-quadruplex structure and pauses at 3'-end of the G-quadruplex forming region when it transverses to the 5'-end of the template. Results from the DNA polymerase stop assay can provide the basis for further studies aimed at elucidating the major G-quadruplexes formed by sequences consisting of more than four runs of contiguous guanines, as well as the specificity of G-quadruplex-interactive molecules in binding different G-quadruplex topologies.

45 Electrochemical investigation of the interaction between G-quadruplex and some ligands using MWCNT modified carbon paste electrode

The G-quadruplex is an unusual DNA secondary structure based on the Hoogesteen G–G base pairing, which stabilizes in the presence of certain metal cations, mainly alkali ions such as K+ (Elahi, Bathaie, Mousavi, Hoshyar, & Ghasemi, 2012). In continuation of our previous studies on the interaction between DNA and small molecules (Ghanbari, Bathaie, Mousavi, 2008; Heli, Bathaie, & Mousavi, 2004), more recently, interaction of G-DNA with polyamines and ethidium bromide was studied (Elahi et al., 2012). In the present study, we investigated the interaction of carotenoids (crocin and crocetin) and monoterpene aldehydes (safranal) of saffron with G-DNA. The MWCNT was ultrasonically treated in 35% solution of nitric acid for 6 h to be functionalized with carboxylic acid groups. The carbon paste electrode was prepared by mixing graphite powder with paraffin at the ratio 65:35. The resulting paste was packed into Teflon tube. The outer layer of the electrode was made of carbon paste modified by the addition of modified MWCNT at the concentration of 10% (w/w). G-DNA was covalently immobilized onto the CPE modified with MWCNT (MWCNT/CPE) in the presence of EDC/NHS. Interaction of G-DNA with the named ligands was investigated by cyclic voltammetry and differential pulse voltammetry using the electroactive complex [Ru(NH3)6]3+ (RuHex). The results showed that crocetin has more affinity than crocin and safranal for binding to G-DNA. Binding constants for these interactions are 4.4 × 104, 1.4 × 104, and 1.6 × 104 M−1 for crocetin, crocin and safranal, respectively.

ChemInform Abstract: Palladium‐Catalyzed Amination of 2‐Chloro‐1‐azaazulene with 2‐Aminopyridine.

AbstractSince compounds (III) and (IV) exhibit a significant change in their absorption and emission spectra in the presence of certain metal cations, they could be potentially used as metal‐cation sensors.

Palladium-Catalyzed Amination of 2-Chloro-1-azaazulene with 2-Aminopyridine

Since compounds (III) and (IV) exhibit a significant change in their absorption and emission spectra in the presence of certain metal cations, they could be potentially used as metal-cation sensors.

Basic iron sulfate — a potential killer in the processing of refractory gold concentrates by pressure oxidation

Refractory gold concentrates often contain submicroscopic gold that is encapsulated within the crystal matrix of iron sulfide minerals, such as pyrite, pyrrhotite and arsenopyrite. To recover the gold, the host mineral must generally be broken down chemically by oxidative processes, such as roasting, pressure oxidation or bacterial leaching, which expose the gold for subsequent recovery by leaching in cyanide solution. The focus of attention in these pretreatment processes is usually the oxidation of the sulfides to elemental sulfur, sulfur dioxide gas or sulfate ions. Less attention is paid to the deportment of iron and the changes in its oxidation state, although this can have a profound effect on gold and silver liberation, as well as downstream operating costs. Iron sulfide minerals break down completely during pressure oxidation, and dissolve in the sulfuric acid solution that is generated from oxidation of the sulfides. This dissolution liberates the tiny gold particles that were originally trapped in the sulfide crystals, and gold recovery during subsequent cyanidation is usually very high (>95%). Iron goes into solution in the oxidation process, initially as ferrous sulfate, but this compound is rapidly oxidized to ferric sulfate, which then hydrolyzes and reprecipitates. The form of the precipitate varies depending on the operating conditions in the autoclave and the presence of certain metal cations. When the acidity in the autoclave is quite low ( 200°C), the formation of hematite is favored. When the acidity is high (>20 g/L H2SO4) and the temperature is relatively low (160 to 200°C), the formation of basic iron sulfate is favored. If the ore or the leach solution contains significant levels of certain cations (such as Na+, K+, NH4+, Ag+ or Pb2+) and the acidity is high (>20 g/L H2SO4), jarosite compounds are favored. Hematite is the desired iron product in the autoclave discharge, for both metallurgical and environmental reasons, but it is difficult to operate an autoclave under the conditions required for effective liberation of gold without converting some of the iron to basic iron sulfate and/or jarosite. These compounds fall into a category of iron compounds known generically as iron hydroxy sulfates, all of which can cause significant processing and environmental problems in the downstream gold process. This paper deals specifically with basic iron sulfate: the conditions under which it is formed in an autoclave, the problems that are caused by its presence in the feed to a cyanidation plant and possible remedial strategies that can be adopted, both in the autoclave and downstream.

Multi-channel receptors based on thiopyrylium functionalised with macrocyclic receptors for the recognition of transition metal cations and anions

We report herein the synthesis and characterization of a family of ligands containing different cation binding sites covalently connected to a thiopyrylium signalling reporter. The receptors L1-L6 are able to signal the presence of certain metal cations via three different channels; i.e. electrochemically, fluorogenically and chromogenically. An acetonitrile solution of L1-L6 shows a bright blue colour due to a charge-transfer band in the 575-585 nm region. The colour variation in acetonitrile of L1-L6 in the presence of the metal cations Ag+, Cd2+, Cu2+, Fe3+, Hg2+, Ni2+, Pb2+ and Zn2+ has been studied. A selective hypsochromic shift of the blue band was found for the systems L4-Pb2+ and L5-Hg2+. Additionally, L1-L6 are poorly fluorescent but coordination with certain metal cations induces an enhancement of the fluorescence at ca 500 nm. For instance, the presence of Cu2+ and Fe3+ induced a remarkable 42-fold and 45-fold enhancement in the emission intensity of L1 centred at 500 nm, respectively. Also remarkable was the 18-fold enhancement observed for L4 and L5 in the presence of Fe3+ and Cu2+, respectively. The electrochemical behaviour of receptors L1-L6 was studied in acetonitrile using platinum as a working electrode and [Bu4N][BF4] as a supporting electrolyte. This family of receptors showed a one-electron reversible redox process at ca. -0.46 V versus sce attributed to the reduction of the thiopyrylium group. A moderate anodic shift in the presence of certain metal cations was observed. The effect in the UV-visible spectra of acetonitrile solutions of receptor L1-L6 in the presence of anions was also studied. A remarkable bleaching was found in the presence of cyanide.

Multi‐Channel Receptors and Their Relation to Guest Chemosensing and Reconfigurable Molecular Logic Gates

AbstractThe synthesis and characterisation of a family of multi‐channel receptors containing crown‐cation binding sites anchored to a 1‐aminophenyl‐1,2,2‐tricyanoethylene group is reported. The ligands L1–L6 bear a 1‐aminophenyl‐1,2,2‐tricyanoethylene scaffolding which is simultaneously a redox‐active group (showing reduction processes at moderately modest potentials) and an acceptor moiety in the 1‐aminophenyl‐1,2,2‐tricyanoethylene chromophore. Additionally, dyes L1–L6 also show fluorescence emission. The colour variation of L1–L6 in acetonitrile in the presence of the metal cations Ag+, Cd2+, Cu2+, Fe3+, Hg2+, Pb2+ and Zn2+ has been studied. Selective hypsochromic shifts were found for the systems L4‐Pb2+, L5‐Hg2+ and L6‐Hg2+. For Hg2+ with L5 and L6 and Pb2+ with L4, emission fluorescence enhancements most likely associated with metal coordination to the anilinium nitrogen were observed. The electrochemical behaviour of receptors L1–L6 was studied in acetonitrile with platinum as working electrode and [Bu4N][BF4] as supporting electrolyte. This family of receptors shows a one‐electron reversible reduction process at around –0.70 V vs. SCE, attributed to the reduction of the tricyanovinyl group. Additionally, all the receptors also show the oxidation of the anilinium moiety at about 1.2–1.4 V vs. SCE. Significant anodic shifts of both reduction and oxidation waves were found in the presence of certain metal cations. The relationship of these multiple‐channel signalling receptors with guest chemosensing and reconfigurable molecular‐based logic gates is discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

HYDROLYSIS OF I131-THYROPROTEIN BY PANCREATIC ENZYMES

Until about 5 years ago, treatment with hot alkali was the most widely used method for hydrolyzing the iodoprotein of thyroid tissue. By such a procedure, Kendall first isolated thyroxine from the thyroid glands of oxen (1). Proteolytic enzymes have also been used for this purpose with varying degrees of success, since the early work of Hutchison (a), Oswald (3), and Harington (4). More recently, the usefulness of enzymic hydrolysis has been extended considerably by combining this method for fragmenting the thyroid protein with the very sensitive techniques of chromatography and radioisotopic labeling for the isolation and identification of the products of hydrolysis. Although this combinat,ion of procedures has been used in several laboratories (5-la), a thorough study of the hydrolysis with proteases has not been reported. In our investigation of this procedure we found, in agreement with Roche et al. (7), that the iodotyrosines are released quite rapidly from the thyroprotein, whereas the release of thyroxine proceeds more slowly. In addition, we found that the yield of thyroxine can be increased by performing the hydrolysis in the presence of certain metal cations (Mn++, Mg++, Ca++). These findings are described below, along with a procedure for the analysis of 1131-labeled thyroid tissue. This procedure requires 10 to 20 hours of hydrolysis, yields approximately 95 per cent recovery of 1131 protein in the form of 1131-amino acids, and results in little release of inorganic I131.