EPR, NMR, and Thermodynamic Evidences for Forced Nuclear Spin–Electron Spin Interactions in the Case of 1-Phenyl-2-Methylpropyl-1,1-Dimethyl-2-Nitroxide (TIPNO) Attached to Permethylated β-Cyclodextrin

In a recent paper (Bardelang et al. in J Org Chem 71:7657–7667, 2006), the deep inclusion of the TIPNO (1-phenyl-2-methylpropyl-1,1-dimethylethyl-2-nitroxide) free radical attached to a permethylated β-cyclodextrin (TRIMEB) into its cavity was questioned. In the present paper it is shown that the results of X-band and W-band electron paramagnetic resonance (EPR) and ¹H nuclear magnetic resonance (NMR) studies of the TIPNO–TRIMEB in the presence of competitors of complexation (1-adamantanol, methyl orange and 1-adamantylamine) are consistent with a situation where the nitroxide is capping the small cavity entrance. The inclusion of the incoming guest was proven by ¹H NMR, whereas no changes in EPR spectra were noticed whatever the competitors’ concentrations. These observations are rationalized in terms of an equilibrium between a nitroxide-capped cyclodextrin (weak complex) and a non-self included form, both species involving competitors’ inclusion without significant EPR spectral changes. These results not only confirm our preliminary findings, but also point out to the peculiar role of the cyclodextrin methoxy crown of the primary rim stabilizing the appended guest by means of weak interactions.     

DNS Analysis of Wall Heat Transfer and Combustion Regimes in a Turbulent Non-premixed Wall-jet Flame

Understanding the heat-release effects on the wall heat transfer in turbulent reacting flows, i.e. heat transfer with or without significant density variation, is essential for a wide variety of industrial flows, especially combustion problems. The present study focuses on the wall heat transfer and the near-wall reaction characteristics. The heat-release effects on the wall heat transfer and skin-friction coefficients are investigated using three-dimensional direct numerical simulations of a turbulent reacting wall-jet flow with and without heat release. Reductions in the skin-friction coefficient are observed in the exothermic case, compared to the isothermal one, and the underlying mechanism is explained. The absolute wall heat flux also increases, while the corresponding Nusselt number decreases with increasing heat release. Furthermore, the wall effects on the near-wall average burning rate are assessed. It is found that the isothermal cold wall results in an appreciable decrease of the burning rate in the exothermic cases. We observed indications that the wall increases the chances for the development of the premixed mode and its occurrence is very fast in the wall-normal direction.     

Force-field and quantum-mechanical binding study of selected SAMPL3 host-guest complexes

A Merck molecular force field classical potential combined with Poisson-Boltzmann electrostatics (MMFF/PB) has been used to estimate the binding free energy of seven guest molecules (six tertiary amines and one primary amine) into a synthetic receptor (acyclic cucurbit[4]uril congener) and two benzimidazoles into cyclic cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]) hosts. In addition, binding enthalpies for the benzimidazoles were calculated with density functional theory (DFT) using the B3LYP functional and a polarizable continuum model (PCM). Although in most cases the MMFF/PB approach returned reasonable agreements with the experiment (±2 kcal/mol), significant, much larger deviations were reported in the case of three host-guest pairs. All four binding enthalpy predictions with the DFT/PCM method suffered 70% or larger deviations from the calorimetry data. Results are discussed in terms of the molecular models used for guest-host complexation and the quality of the intermolecular potentials.     

Coupled Turbulent Flow Chromatography: LC–MS/MS Method for the Analysis of Pesticide Residues in Grapes, Baby Food and Wheat Flour Matrices

This paper describes an on-line sample preparation method for the simultaneous determination of 48 pesticides in grapes, baby food and wheat flour matrices. Target pesticides were selected to represent a wide variety of chemical structures and three typical matrices were selected. Turbulent flow chromatography was applied for on-line sample cleanup directly coupled to LC?CMS/MS. The aim of the method was to reduce total analysis time, eliminate manual laboratory work, provide clean extracts and achieve reproducible results. Single laboratory method validation was conducted establishing limits of detection between 0.8 and 6.0?ng?g^?1 for baby food, and 0.8?C10.3?ng?g^?1 for other matrices. Within-day precision values varied between 4 and 18?%, while between-day precisions were in the range 5?C22?%. Method recovery ranged from 67 to 124?%, and method accuracy was demonstrated by analysis of external quality control samples. The method was also tested on 24 different survey samples from both bio and organic origin. The method was shown to be convenient, fast and fit for purpose in meeting regulatory requirements for pesticide residue monitoring.     

Synthesis,solid-state photophysical properties and electropolymerization of novel diazulenyl ethenes

The novel 1,2-di(azulen-1-yl)cyclopent-1-ene 3 was conveniently synthesized via a two-step procedure involving Vilsmeier–Haack acylation of azulene with N,N,N′,N′-tetraethylglutaramide (TEGA) and POCl₃, followed by an intramolecular McMurry coupling of the resulting diketone. In contrast with the previously reported (E)-1,2-di(azulen-1-yl)ethene that shows negligible fluorescence in the solid state, alkene 3 displays fluorescence emission from the S₂ excited state of the azulene moieties. This compound easily polymerizes upon electrochemical oxidation, leading to the formation of a conducting polymer film at the electrode surface.     

PACIAE model capability in describing net proton moments

PACIAE 2.0, a parton and hadron cascade model, is employed to investigate the dependence of the moments of net proton event distributions on reaction energies varying from RHIC to LHC energy in p + p collisions. It is found that net proton moments and moment products are sensitive to the collision energy except the moment product k?? ² which is almost independent of the collision energy. The PACIAE results are in line with experimental data.     

Adaptive Neuro-Fuzzy Inference System and a Multilayer Perceptron Model Trained with Grey Wolf Optimizer for Predicting Solar Diffuse Fraction

The accurate prediction of the solar diffuse fraction (DF), sometimes called the diffuse ratio, is an important topic for solar energy research. In the present study, the current state of Diffuse irradiance research is discussed and then three robust, machine learning (ML) models are examined using a large dataset (almost eight years) of hourly readings from Almeria, Spain. The ML models used herein, are a hybrid adaptive network-based fuzzy inference system (ANFIS), a single multi-layer perceptron (MLP) and a hybrid multi-layer perceptron grey wolf optimizer (MLP-GWO). These models were evaluated for their predictive precision, using various solar and DF irradiance data, from Spain. The results were then evaluated using frequently used evaluation criteria, the mean absolute error (MAE), mean error (ME) and the root mean square error (RMSE). The results showed that the MLP-GWO model, followed by the ANFIS model, provided a higher performance in both the training and the testing procedures.     

Electrospray ionization mass spectrometric study of encapsulation of amino acids by cyclodextrins

Electrospray ionization (ESI) mass spectrometry has been used to study inclusion (host-guest) complexes of cyclodextrins (CDs) with amino acids. Host-guest complexes formed in solution are stable for characterization by ESI mass spectrometry: The relative abundances and the stoichiometry of the complexes formed in solution can, thus, be determined in the gas phase. The studies verified that β- and γ-cyclodextrin better accommodate protonated amino acids than α-cyclodextrin, and that chemically modified cyclodextrins such as heptakis(2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD) may show profound improvement in complexation. The preferential formation of DM-β-CD-aromatic amino acid over DM-β-CD-aliphatic amino acid complexes is confirmed by the experiments, and the relative gas-phase stabilities determined by repeller-collimator collision-induced dissociation show an identical trend to the complexation in solution. Although molecular mechanics studies also may predict the encapsulation preference of protonated amino acids by cyclodextrins, only small differences in the total complexation energies are obtained because of the inability of the calculations to consider hydrophobic interactions. An experimental approach based on ESI mass spectrometry is, therefore, more reliable in predicting host-guest interactions that involve cyclodextrins and amino acids than the theoretical calculations that employ molecular mechanics models.     

Baer modules over valuation domains

Summary A module B over a commutative domain R is said to be a Baer module if Ext _R ¹ (B, T)=0for all torsion R-modules T. The case in which R is an arbitrary valuation domain is investigated, and it is shown that in this case Baer modules are necessarily free. The method employed is totally different from Griffith's method for R=Z which breaks down for non-hereditary rings.This research was partially supported by NSF Grants DMS-8400451 and DMS-8500933.