The Collision Cross Sections of Iodide Salt Cluster Ions in Air via Differential Mobility Analysis-Mass Spectrometry

To date, most collision cross section (CCS) predictions have invoked gas molecule impingement-reemission rules in which specular and elastic scattering of spherical gas molecules from rigid polyatomic surfaces are assumed. Although such predictions have been shown to agree well with CCSs measured in helium bath gas, a number of studies reveal that these predictions do not agree with CCSs for ions in diatomic gases, namely, air and molecular nitrogen. To further examine the validity of specular-elastic versus diffuse-inelastic scattering models, we measured the CCSs of positively charged metal iodide cluster ions of the form [MI]_n[M⁺]_z, where M?=?Na, K, Rb, or Cs, n?=?1 – 25, and z?=?1 – 2. Measurements were made in air via differential mobility analysis mass spectrometry (DMA-MS). The CCSs measured are compared with specular-elastic as well as diffuse-inelastic scattering model predictions with candidate ion structures determined from density functional theory. It is found that predictions from diffuse-inelastic collision models agree well (within 5 %) with measurements from sodium iodide cluster ions, while specular-elastic collision model predictions are in better agreement with cesium iodide cluster ion measurements. The agreement with diffuse-inelastic and specular-elastic predictions decreases and increases, respectively, with increasing cation mass. However, even when diffuse-inelastic cluster ion predictions disagree with measurements, the disagreement is of a near-constant factor for all ions, indicating that a simple linear rescaling collapses predictions to measurements. Conversely, rescaling cannot be used to collapse specular-elastic predictions to measurements; hence, although the precise impingement reemission rules remain ambiguous, they are not specular-elastic.

Transiting the molecular potential energy surface along low energy pathways: The TRREAT algorithm

The Transition Rapidly exploring Random Eigenvector Assisted Tree (TRREAT) algorithm is introduced to perform searches along low curvature pathways on a potential energy surface (PES). The method combines local curvature information about the PES with an iterative Rapidly exploring Random Tree algorithm (LaValle, Computer Science Department, Iowa State University, 1998, TR98–11) that quickly searches high‐dimensional spaces for feasible pathways between local minima. Herein, the method is applied to identifying conformational changes of molecular systems using Cartesian coordinates while avoiding a priori definition of collective variables. We analyze the pathway identification problem for alanine dipeptide, cyclohexane and glycine using nonreactive and reactive forcefields. We show how TRREAT‐identified pathways can be used as valuable input guesses for double‐ended methods such as the Nudged Elastic Band when ascertaining transition state energies. This method can be utilized to improve/extend the reaction databases that lie at the core of automatic chemical reaction mechanism generator software currently developed to build kinetic models of chemical reactions. © 2013 Wiley Periodicals, Inc.     

Simple Reduction of Heteroaromatic Esters to Alcohols Using a Sodium Borohydride–Methanol System

Some heteroaromatic esters were reduced to the corresponding alcohols by using a sodium borohydride–methanol system. The reduction was completed within 0.15–2.0 h in refluxing THF. The alcohol products were isolated after aqueous workup in moderate to excellent yield (48–97%).     

Binding of Ionic Pyrene Derivatives to Polyelectrolytes. A Uv Absorption and Fluorescence Study

Abstract

The binding of pyrenesulfonic acid and pyrenebutyric acid to poly(vinyl benzyl trimethylammonium) chloride was investigated by UV and fluorescence spectroscopy. It was found that the binding constant was 7.5 × 10⁴ and 3.5 × 10⁴M^?1, respectively. The addition of the polyelectrolyte quenches the fluorescence of the pyrene group, and at the same time the typical excimer emission appears. This emission originates in pre-formed ground state aggregates of the pyrene derivatives incorporated into the polyion domain. Similar effects were observed when anionic polyelectrolytes, poly(styrene sulfonic), and poly(vinyl sulfonic) acids were added to cationic pyrene derivatives. The binding constants depend on the length of the aliphatic sidechain of the derivatives.     

Cyclopalladation and Reactivity of Amino Esters through C?H Bond Activation: Experimental,Kinetic, and Density Functional Theory Mechanistic Studies

The orthopalladation, through C? H bond activation, of a large number of amino esters and amino phosphonates derived from phenylglycine, and having different substituents at the aryl ring and the C‐α atom, as well as on the N‐amine atom, has been studied. The experimental observations indicated an improvement in the yields of the orthopalladated compounds when the N‐amine and/or the C‐α atom are substituted, when compared with the unsubstituted methyl phenylglycinate derivatives. In contrast, substitutions at the aryl ring do not promote significant changes in the orthometalation results. Furthermore, the use of hydrochloride salts of the amino esters has also been shown to have a remarkably favorable effect on the process. All these observations have been fully quantified at different temperatures and pressures by a detailed kinetic study in solution in different solvents and in the presence and absence of added Brønsted acids and chloride anions. The data collected indicate relevant changes in the process depending on these conditions, as expected from the general background known for cyclopalladation reactions. An electronic mechanism of the orthopalladation has been proposed based on DFT calculations at the B3LYP level, and a very good agreement between the trends kinetically measured and the theoretically calculated activation barriers has been obtained. The reactivity of the new orthopalladated amino phosphonate derivatives has been tested and it was found that their halogenation, alkoxylation and carbonylation resulted in formation of the corresponding functionalized ortho‐haloaminophosphonates, ortho‐alkoxyaminophosphonates and oxoisoindolinylphosphonates.     

VISIBLE CHEMILUMINESCENCE ASSOCIATED WITH THE REACTION BETWEEN METHEMOGLOBIN OR OXYHEMOGLOBIN WITH HYDROGEN PEROXIDE

Abstract Visible chemiluminescence is emitted in the irreversible deactivation of hemoglobin or methemoglobin with excess H₂O₂. The emission takes place in two phases. The most intense one lasts a few seconds and is followed by a second phase of lower intensity that remains for longer periods. This second phase presents chaotic or sustained oscillations. Free radicals are implicated in the luminescent process since the emission can be reduced by free radical scavengers such as 6-hydroxy-2,5,7,8,-tetramethylchroman-2-carboxylic acid (Trolox) or ascorbic acid. These additives lead to a delay in reaching the maximum intensity, which can be related to their consumption, implying substantial recycling of the hemoprotein. Chemiluminescence is also observed in the oxidation of hemin by H₂O₂, suggesting a role for the heme group in the processes leading to the excited state production. The lower intensity observed in the presence of hemin can be related to the contribution of the globin chains.     

Xylanolytic enzyme production by anAspergillus niger isolate

Production of xylanolytic enzymes by anAspergillus niger CCMI 850 isolate was investigated in batch cultures. The effect of the composition of a fermentation medium that did not include chemical inducers, on β-xylanase, β-xylosidase, α-l-arabinofuranosidase, and total cellulase activity was studied. With 4% xylan as the carbon source, about 65 U/mL of β-xylanase was obtained, whereas the total cellulase activity was undetectable, under the specified conditions. This β-xylanase activity represents the highest reported for a wild-type strain ofA. niger. The effect of pH and temperature on the activity of β-xylanase was studied. Partial characterization of the β-xylanase showed that with insoluble birchwood as substrate theK _m andV _max were 0.3 mM and 19 μmol/min, respectively. Aspects of using the crude β-xylanase preparation for applications in the pulp and paper industry were discussed.     

A method to calculate density distribution of adsorption centers from temperature-programmed desorption spectra

A new method to calculate the function of density distribution of adsorption centers according to the activation energies of desorption by using temperature-programmed desorption curves is suggested. The application of this method is exemplified by toluene desorption from ZSM-5 zeolite.

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Tetragonal to monoclinic phase transition observed during Zr anodisation

Plasma electrolytic oxidation (PEO) is a coating procedure that utilises anodic oxidation in aqueous electrolytes above the dielectric breakdown voltage to produce oxide coatings that have specific properties. These conditions facilitate oxide formation under localised high temperatures and pressures that originate from short-lived microdischarges at sites over the metal surface and have fast oxide volume expansion. Anodic ZrO₂ films were prepared by subjecting metallic zirconium to PEO in acid solutions (H₂C₂O₄ and H₃PO₄) using a galvanostatic DC regime. The ZrO₂ microstructure was investigated in films that were prepared at different charge densities. During the anodic breakdown, an important change in the amplitude of the voltage oscillations at a specific charge density was observed (i.e., the transition charge density (Q ^T)). We verified that this transition charge is a monotonic function of both the current density and temperature applied during the anodisation, which indicated that Q ^T is an intrinsic response of this system. The oxide morphology and microstructure were characterised using SEM and X-ray diffraction experiments (XRD) techniques. X-ray diffraction analysis revealed that the change in voltage oscillation was correlated with oxide microstructure changes during the breakdown process.