Complexation of metal ions with the novel diazadithia crown ethers carrying two pyrene pendants in acetonitrile-tetrahydrofuran

Two crown ethers carrying pyrene side arms with nitrogen-sulfur donor atom were designed and synthesized by the reaction of the corresponding macrocyclic compounds and 1-bromomethyl-pyrene. The influence of metal cations such as Al³⁺, Zn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Mn²⁺, Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ on the spectroscopic properties of the ligands was investigated in acetonitrile-tetrahydrofuran (1:1) by means of absorption and emission spectrometry. Absorption spectra show isosbestic points in the spectrophotometric titration of Al³⁺, Zn²⁺, Fe²⁺, Ni²⁺, Cu²⁺, and Pb²⁺ with 16-membered crown ether. Similar results were obtained for Al³⁺, Fe²⁺, Hg²⁺, Cu²⁺ and Pb²⁺ with 14-membered crown ether. The results of spectrophotometric titration experiments disclosed the complexation stoichiometry and complex stability constants of the novel ligands with these cations. According to spectrofluorimetric titration measurements the 14-membered diazadithia crown ether showed sensitivity for Pb²⁺ with linear range and detection limit of 1.3 × 10^?6 to 5.2 × 10^?5 M and 5.2 × 10^?7 M, respectively. The 16-membered diazadithia crown ether showed sensitivity for Ni²⁺ with linear range and detection limit of 1.3 × 10^?7 to 5.2 × 10^?6 M and 4.1 × 10^?8 M, respectively.     

Fluorescence study on the interaction of bovine serum albumin with two coumarin derivatives

The interactions between bovine serum albumin (BSA) and two substituted hydroxychromone derivatives of coumarin, 3-hydroxy-7,8,9,10-tetrahydro-6H-benzo[c]chromen-6-on (C₃) and 1,3-dihydroxy-7,8,9,10-tetrahy-dro-6H-benzo[c]chromen-6-on (C_1.3), were investigated by fluorescence quenching spectra and UV-vis absorption spectra. It was proved that the fluorescence quenching of BSA by C₃ and C_{1, 3} was mainly a result of the formation of C₃ and C_1.3-BSA complexes. The Stern-Volmer quenching constants, binding constants, binding sites and the corresponding thermodynamic parameters ΔH ^o, ΔS ^o and ΔG ^o at different temperatures were calculated. The results indicated that van der Waals interactions and hydrogen bonds were the predominant intermolecular forces in stabilizing each complex. The detection limits of C₃ and C_1.3 were 5.08 × 10⁻⁷ and 1.11 × 10⁻⁷ M in the presence of BSA, respectively.     

Arsenic-induced protein phosphorylation changes in HeLa cells

Arsenic is well documented as a chemotherapeutic agent capable of inducing cell death while at the same time is considered a human carcinogen and an environmental contaminant. Although arsenic toxicity is well known and has formed an impressive literature over the time, little is known about how its effects are exerted at the proteome level. Protein phosphorylation is an important post-translational modification involved in the regulation of cell signaling and likely is altered by arsenic treatment. Despite the importance of phosphorylation for many regulatory processes in cells, the identification and characterization of phosphorylation, as effected by arsenic through mass spectrometric detection, are not fully studied. Here, we identify phosphorylated proteins, which are related to post-translational modifications after phenylarsine oxide (PAO) inoculation to HeLa cells. PAO was chosen because of its high cytotoxicity, measured earlier in these labs. In this study, size exclusion chromatography coupled to inductively coupled plasma mass spectrometry (SEC-ICP-MS) is used to establish several molecular weight fractions with phosphorylated proteins by monitoring ³¹P signal vs. time via ICP-MS. SEC-ICP-MS fractions are collected and then separated by the nano-LC-CHIP/ITMS system for peptide determination. Spectrum Mill and MASCOT protein database search engines are used for protein identification. Several phosphorylation sites and proteins related to post-translational modifications are also identified.     

Fe vibrational spectroscopy of myoglobin and cytochrome f

The Fe vibrational density of states (VDOS) has been determined for the heme proteins deoxymyoglobin, metmyoglobin, and cytochrome f in the oxidized and reduced states, using nuclear resonance vibrational spectroscopy (NRVS). For cytochrome f in particular, the NRVS spectrum is compared with multiwavelength resonance Raman spectra to identify those Raman modes with significant Fe displacement. Modes not seen by Raman due to optical selection rules appear in the NRVS spectrum. The mean Fe force constant extracted from the VDOS illustrates how Fe dynamics varies among these four monoheme proteins, and is correlated with oxidation and spin state trends seen in model heme compounds. The protein's contribution to Fe motion is dominant at low frequencies, where coupling to the backbone tightly constrains Fe displacements in cytochrome f, in contrast to enhanced heme flexibility in myoglobin.     

Noniron isotopes

Hyperfine Interactions - This article reports on experimental developments and first results for Mössbauer isotopes other than 57Fe. We will restrict ourselves to basic features of the...     

Sensitive voltammetric assay of etoposide using modified glassy carbon electrode with a dispersion of multi-walled carbon nanotube

A sensitive electroanalytical method for the determination of anticancer drug etoposide (ETP) using adsorptive stripping differential pulse voltammetry (AdSDPV) at a multi-walled carbon nanotube-modified glassy carbon electrode (MWCNT-modified GCE) is presented. The surface morphology of modified electrode was characterized by scanning electron microscopy. The effects of accumulation time and potential, pH, scan rate, and amount of MWCNT suspension were investigated. The calibration curve was linear in the concentration range of 2.0?×?10^?8–2.0?×?10^?6 M with the detection limit of 5.4?×?10^?9 M. The reproducibility of the peak current was found at 1.55 % (n?=?5) RSD value in pH 6.0 Britton–Robinson buffer for the MWCNT-modified GCE. The method was then successfully utilized for the determination of ETP in pharmaceutical dosage form, and a recovery of 99.55 % was obtained. The possible oxidation mechanism of ETP was also discussed. The proposed electroanalytical method using MWCNT-modified GCE is the most sensitive method for the determination of ETP with lowest limit of detection in the previously published electrochemical methods.     

The Galois closure of Drinfeld modular towers

In this article we study Drinfeld modular curves X₀(pn) associated to congruence subgroups Γ₀(pn) of GL(2,Fq[T]) where p is a prime of Fq[T]. For n>r>0 we compute the extension degrees and investigate the structure of the Galois closures of the covers X₀(pn)→X₀(pr) and some of their variations. The results have some immediate implications for the Galois closures of two well-known optimal wild towers of function fields over finite fields introduced by Garcia and Stichtenoth, for which the modular interpretation was given by Elkies.     

Nanostructured core-shell Ni deposition on SiC particles by alkaline electroless coating

In this study, core-shell nanostructured nickel formation on silicon carbide (SiC) ceramic powders was achieved through the electroless deposition method using alkaline solutions. To produce a nano core-shell Ni deposition on the SiC surfaces, process parameters such as pH values, the type of reducer material, deposition temperature, stirring rate and activation procedure among others were determined. Full coverage of core-shell nickel structures on SiC surfaces was achieved with a grain size of between 100 and 300 nm, which was approximately the same deposition thickness on the SiC surfaces. The surface morphology of the coated SiC particles showed a homogenous distribution of nanostructured nickel grains characterized by scanning electron microscopy and X-ray diffraction techniques. The nanostructures of the crystalline Ni coatings were observed to be attractive for achieving both good bonding and dense structure. The thin core shell-structure of Ni on the SiC surfaces was assessed as a beneficial reinforcement for possible metal matrix composite manufacturing.     

Compressed images for affinity prediction (CIFAP): a study on predicting binding affinities for checkpoint kinase 1 protein inhibitors

Analyses of known protein–ligand interactions play an important role in designing novel and efficient drugs, contributing to drug discovery and development. Recently, machine learning methods have proven useful in the design of novel drugs, which utilize intelligent techniques to predict the outcome of unknown protein–ligand interactions by learning from the physical and geometrical properties of known protein–ligand interactions. The aim of this study is to work through a specific example of a novel computational method, namely compressed images for affinity prediction (CIFAP), in which binding affinities for structurally related ligands in complexes with human checkpoint kinase 1 (CHK1) are predicted. The CIFAP algorithm presented here relates published pIC ₅₀ values of 57 compounds, derived from a thienopyridine pharmacophore, in complexes with CHK1 to their two‐dimensional (2D) electrostatic potential images compressed in orthogonal dimensions. Patterns obtained from the 2D images are then used as inputs in regression and learning algorithms such as support vector regression (SVR) and adaptive neuro‐fuzzy inference system (ANFIS) methods to validate the experimental pIC ₅₀ values. This study revealed that the 2D image pixels in the vicinity of bound ligand surfaces provide more relevant information to make correlations with the empirical pIC ₅₀ values. As compared with ANFIS, SVR gave rise to the lowest root mean square errors and the greatest correlations, suggesting that SVR could be a plausible choice of machine learning methods in predicting binding affinities by CIFAP. Copyright © 2013 John Wiley & Sons, Ltd.