Laser-spectroscopic laboratory studies of atmospheric aqueous phase free radical chemistry

Nitrate radical (NO₃) reactions with benzene (R-1), toluene (R-2), p-xylene (R-3), p-cresol (R-4) and mesitylene (R-5) have been studied by laser photolysis/long path laser absorption (LP-LPLA) in aqueous solution. Rate constants of k₁=(4.0±0.6) 10⁸, k₂=(1.2±0.3)10⁹, k₃=(1.6±0.1)10⁹, k₄= (8.4±2.3)10⁸ and k₅=(1.3±0.3)10⁹ lmol^-1s^-1 were obtained at T=298 K. In addition, reaction rate coefficients for SO^-₅+Fe²⁺prod. (R-6) and SO^-₅+Mn²⁺prod. (R-7) of k₆=(4.3±2.4) 10⁷ lmol^-1s^-1 and k₇=(4.6±1.0)10⁶ lmol^-1s^-1 (T=298 K, I0) have been obtained by the application of laser photolysis/UV-VIS broadband diode array spectroscopy. A new laser photolysis/UV-long path laser absorption experiment has been applied to study the reaction of the Cl^-₂ radical anion with dissolved sulfur(IV). For the reactions Cl^-₂+HSO^-₃2Cl^-+H⁺+SO^-₃ (R-8) and Cl^-₂+SO^2-₃2Cl^-+SO^-₃ (R-9) rate coefficients of k₈=(1.7±0.2)10⁸ lmol^-1s^-1 (T=298 K, I0) and of k₉=(6.2±0.3)10⁷ lmol^-1s^-1 (T=279 K, I0) were obtained.     

Biosynthetic Production of [N2,1,3,7,9-15N]Guanosine and [1,3,7,9-15N]inosine and conversion into [N6,1,3,7,9-15N]adenosine for structure elucidation of RNA by heteronuclear NMR

A procedure was developed for the biosynthetic preparation of ¹⁵N-labelled guanosine and inosine through the action of a mutant Bacillus subtilis strain. Crude [N²,1,3,7,9-¹⁵N]guanosine and [1,3,7,9-¹⁵N]inosine were isolated from the culture filtrate by precipitation and anion-exchange chromatography (Scheme 1). No cell lysis and no enzymatic degradation was necessary. The per-isobutyrylated derivatives 1 and 2 were isolated from a complex mixture, purified by virtue of their different lipophilicity, and separated in three steps involving normal-and reversed-phase silica-gel chromatography. One litre of complex nutrient medium yielded 8.44 mmol of guanosine derivative and 2.84 mmol of inosine derivative with high average ¹⁵N enrichment (83.5 and 91.9 atom-%, resp.). [N⁶,1,3,7,9-¹⁵N]Adenosine ( 4 ) was obtained from 2′,3′,5′-tri-O-isobutyryl[1,3,7,9-¹⁵N]inosine ( 1 ) through the ammonolysis of its 1,2,4-triazolyl derivative with aqueous ¹⁵NH₃ (Scheme 2).     

Stable Methods for Evaluating the Points cos(i{pi}/n)

A variety of alternative methods for evaluating cos(i/n) fori= 0, 1,...,n are compared theoretically and experimentally,and the best ones selected on the basis of accuracy and thecomputational efficiency. The error analysis involved demonstrateshow certain mathematically equivalent recurence relations canexhibit very different computational behaviour.     

Structure and cooperativity of the hydrogen bonds in sodium dihydrogen triacetate

Geometry and energetics of low energy conformers of sodium dihydrogen triacetate (SDHTA) and its anion are studied using density functional theory (DFT) at the Becke, Lee‐Yang‐Parr hybrid functional (BLYP) and Becke, three‐parameter, Lee‐Yang‐Parr hybrid functional (B3LYP) levels. For both cases, two structures of comparable energy are found, which have different symmetry with respect to the two hydrogen bonds (HBs). DFT‐based Born–Oppenheimer molecular dynamics simulations are performed for SDHTA, which show that both structures are visited at room temperature conditions. The trajectory analysis further reveals that the two HBs behave anticooperative, that is, on average elongation of one HB is accompanied by a compression of the other one. This is in accord with nuclear magnetic resonance (NMR) experimental studies for a similar counter ion–dihydrogen triacetate complex. © 2012 Wiley Periodicals, Inc.     

Synthesis of Stereochemically Flexible Cyclic Biphenylbisphosphinite Ligands: Control of the Dynamics and Selectivity

Novel l -tartaric acid based stereodynamic biphenylbisphosphinite ligands with anilino linkers were prepared as cyclic diamide compounds. The influence of the constitutional substitution pattern of the amino group at the aniline moiety on the diastereoselective formation of the ligand was investigated. While the meta-anilino bridged ligands showed a highly dynamic behavior and no discrimination between (R_ax) and (S_ax) configuration, l -tartaric acid substitution on ortho-anilino bridged ligands leads to diastereoselective self-alignment of the central biphenol axis, which controls the stereoselectivity of the ligand and catalyst. The experimental findings were corroborated by theoretical calculations. In the rhodium-catalyzed enantioselective hydrogenation of methyl 2-acetamidoacrylate (MAA), an enantiomeric ratio of 75 : 25 (R/S) was obtained for the ortho-substituted ligand.     

Gårding's Theory of Hyperbolic Polynomials

This paper presents a simple, self‐contained account of Gårding's theory of hyperbolic polynomials, together with a recent convexity result of Bauschke‐Güler‐Lewis‐Sendov and an inequality of Gurvits. This account begins by establishing some new results. The first concerns the existence of a pointwise arrangement of the eigenvalues so that they become global real analytic functions. The second asserts that the associated “branches” are independent of the choice of hyperbolic direction. © 2013 Wiley Periodicals, Inc.     

Montecrinanes A–C: Triterpenes with an Unprecedented Rearranged Tetracyclic Skeleton from Celastrus vulcanicola. Insights into Triterpenoid Biosynthesis Based on DFT Calculations

Three new triterpenoids with an unprecedented 6/6/6/6‐fused tetracyclic carbon skeleton, montecrinanes A–C ( 1 – 3 ), were isolated from the root bark of Celastrus vulcanicola, along with known D:B‐friedobaccharanes ( 4 – 6 ), and lupane‐type triterpenes ( 7 – 12 ). The stereostructures of the new metabolites were elucidated based on spectroscopic (1D and 2D NMR) and spectrometric (HR‐EIMS and HR‐ESIMS) techniques. Their absolute configurations were determined by both NMR spectroscopy, with (R)‐(?)‐α‐methoxyphenylacetic acid as a chiral derivatizing agent, and biogenetic considerations. Biogenetic pathways for montecrinane and D:B‐friedobaccharane skeletons were proposed and studied by DFT methods. The theoretical results support the energetic feasibility of the putative biogenetic pathways, in which the 1,2‐methyl shift from the secondary baccharenyl cation represents a novel and key reaction step for a new montecrinane skeleton.     

Autonomously Propelled Motors for Value‐Added Product Synthesis and Purification

A proof‐of‐concept design for autonomous, self‐propelling motors towards value‐added product synthesis and separation is presented. The hybrid motor design consists of two distinct functional blocks. The first, a sodium borohydride (NaBH₄) granule, serves both as a reaction prerequisite for the reduction of vanillin and also as a localized solid‐state fuel in the reaction mixture. The second capping functional block consisting of a graphene–polymer composite serves as a hydrophobic matrix to attract the reaction product vanillyl alcohol (VA), resulting in facile separation of this edible value‐added product. These autonomously propelled motors were fabricated at a length scale down to 400 μm, and once introduced in the reaction environment showed rapid bubble‐propulsion followed by high‐purity separation of the reaction product (VA) by the virtue of the graphene–polymer cap acting as a mesoporous sponge. The concept has excellent potential towards the synthesis/isolation of industrially important compounds, affinity‐based product separation, pollutant remediation (such as heavy metal chelation/adsorption), as well as localized fuel‐gradients as an alternative to external fuel dependency.