The presentation of an approach for estimating the intramolecular hydrogen bond strength in conformational study of β-Aminoacrolein

All the plausible conformations of β-aminoacrolein (AMAC) have been investigated by the Bekes-Lee-Yang-Parr (B3LYP) nonlocal density functional with extended 6-311++G** basis set for studying the stability order of conformers and the various possibilities of intramolecular hydrogen bonding formation. In general the ketoamine (KA) conformers of AMAC, by mean average, are more stable than the corresponding enolimine (EI) and ketoimine (KI) analogues and this stability is mainly due to the π-electron resonance in these conformers that established by NH2 functional group. The contribution of resonance to the stability of chelated KA conformers is about 75.6 kJ/mol, which is greater than that of the hydrogen bond energy (E_HB=35.0 kJ/mol). The relative decreasing order of the various hydrogen bond energies was found to be: O–HN_imine(strong)>N_amine-HO_keto (normal)>N_imine-HO_hydroxyl (weak) > N_imine-HO_keto (weak). Hydrogen bond energies for all systems were obtained from the method that we called related rotamers method (RRM). The topological properties of the electron density contributions for various type of intramolecular hydrogen bond have been analyzed in term of the Bader theory of atoms in molecules (AIM). The results of these calculations support the previous calculations, which obtained by the related rotamer methods.     

A Computational Study of 3‐D Helium Clusters

Physical and thermodynamic properties have been calculated and analyzed for the best and optimized geometries of the 3‐D clusters with N = 3 to N = 10 atoms and unit cells of three types of crystalline systems using ab initio RHF/6–31G^** method. Dependence of the lattice binding energy on the cluster parameter, R, has been studied. Similar behavior observed for the binding energies for all clusters shows that probabilities of their existence in the condensed phase are more or less the same. In the next step, thermodynamic properties have been calculated and analyzed for He₂₇ 3‐D helium clusters with simple cubic, body centered cubic (bcc), trigonal and hexagonal (hcp) configurations. The results show that the hexagonal cluster is more favored over other clusters. It is found that these clusters are electronically stable over a limited range of the values for the lattice parameter. Δ_fH is constant in this stability region and thus the Δ_fG exactly follows the variations of TΔ_fS. Surface effects have been investigated by comparing the square and hexagonal He₉ 2‐D lattices with the cubic and hexagonal He₂₇ 3‐D lattices, respectively. The lattice parameters, densities and molar volumes calculated for the clusters with hcp and bcc configurations have satisfactory agreement with the available experimental values. Properties of the He₁₃, He₃₄ and He₁₀₄ hcp clusters have also been calculated and analyzed.     

Fabrication of Fe3O4@graphene oxide core-shell nanospheres for ferrofluid-based dispersive solid phase extraction as exemplified for Cd(II) as a model analyte

Microchimica Acta - The authors describe the synthesis of core-shell structured Fe3O4@graphene oxide nanospheres (denoted as Fe3O4@GO NSs) via a chemical (covalent) bonding method. A chemical...     

Determination of Trihalomethanes in Drinking Water by Dispersive Liquid–Liquid Microextraction then Gas Chromatography with Electron-Capture Detection

Dispersive liquid–liquid microextraction (DLLME) has been used for preconcentration of trihalomethanes (THMs) in drinking water. In DLLME an appropriate mixture of an extraction solvent (20.0 μL carbon disulfide) and a disperser solvent (0.50 mL acetone) was used to form a cloudy solution from a 5.00-mL aqueous sample containing the analytes. After phase separation by centrifugation the enriched analytes in the settled phase (6.5 ± 0.3 μL) were determined by gas chromatography with electron-capture detection (GC–ECD). Different experimental conditions, for example type and volume of extraction solvent, type and volume of disperser solvent, extraction time, and use of salt, were investigated. After optimization of the conditions the enrichment factor ranged from 116 to 355 and the limit of detection from 0.005 to 0.040 μg L⁻¹. The linear range was 0.01–50 μg L⁻¹ (more than three orders of magnitude). Relative standard deviations (RSDs) for 2.00 μg L⁻¹ THMs in water, with internal standard, were in the range 1.3–5.9% (n = 5); without internal standard they were in the range 3.7–8.6% (n = 5). The method was successfully used for extraction and determination of THMs in drinking water. The results showed that total concentrations of THMs in drinking water from two areas of Tehran, Iran, were approximately 10.9 and 14.1 μg L⁻¹. Relative recoveries from samples of drinking water spiked at levels of 2.00 and 5.00 μg L⁻¹ were 95.0–107.8 and 92.2–100.9%, respectively. Comparison of this method with other methods indicates DLLME is a very simple and rapid (less than 2 min) method which requires a small volume of sample (5 mL).     

Determination of amine and aldehyde surface densities: application to the study of aged plasma treated polyethylene films

The aim of this work was to test and to compare different methods reported in the literature to quantify amine and aldehyde functions on the surface of polyethylene (PE) films treated by ammonia plasma and to specify their stability against time. A low pressure ammonia plasma reactor was used to functionalize PE films with amine groups, which could be subsequently used for further immobilization of biomolecules. In order to determine the density of amine groups on the surface of treated films, various molecule probes and spectrophotometric analytical methods have been investigated. Two methods using (i) sulfosuccinimidyl 6-[3'-(2-pyridyldithio)-propionamido] hexanoate (sulfo-LC-SPDP) and (ii) 2-iminothiolane (ITL) associated with bicinchoninic acid (BCA) have been proved to be reliable and sensitive enough to estimate the surface concentration of primary amine functions. The amount of primary amino groups on the functionalized polyethylene films was found to be between 1.2 and 1.4 molecules/nm2. In a second step, the surface concentration of glutaraldehyde (GA), which is currently used as a spacer arm before immobilization of biomolecules, has been assessed: two methods were used to determine the surface density of available aldehyde functions, after the reaction of GA with the aminated polyethylene film. The concentration of GA was found to be in the same range as primary amine concentration. The influence of aging time on the density of available amino and aldehyde groups on the surfaces were evaluated under different storage conditions. The results showed that 50% of the initial density of primary amine functions remained available after storage during 6 days of the PE samples in PBS (pH 7.6) at 4 degrees C. In the case of aldehyde groups, the same percentage of the initial density (50%) remained active after storage in air at RT over a longer period, i.e., 15 days.     

An assessment of theoretical procedures for π-conjugation stabilisation energies in enones

We introduce a representative database of 22 α,β- to β,γ-enecarbonyl isomerisation energies (to be known as the EIE22 data-set). Accurate reaction energies are obtained at the complete basis-set limit CCSD(T) level by means of the high-level W1-F12 thermochemical protocol. The isomerisation reactions involve a migration of one double bond that breaks the conjugated π-system. The considered enecarbonyls involve a range of common functional groups (e.g., Me, NH₂, OMe, F, and CN). Apart from π-conjugation effects, the chemical environments are largely conserved on the two sides of the reactions and therefore the EIE22 data-set allows us to assess the performance of a variety of density functional theory (DFT) procedures for the calculation of π-conjugation stabilisation energies in enecarbonyls. We find that, with few exceptions (M05-2X, M06-2X, BMK, and BH&;HLYP), all the conventional DFT procedures attain root mean square deviations (RMSDs) between 5.0 and 11.7 kJ mol^?1. The range-separated and double-hybrid DFT procedures, on the other hand, show good performance with RMSDs below the ‘chemical accuracy’ threshold. We also examine the performance of composite and standard ab initio procedures. Of these, SCS-MP2 offers the best performance-to-computational cost ratio with an RMSD of 0.8 kJ mol^?1.     

Electron spin resonance spectra of nitrogen heterocyclic radical ions

Abstract

We introduce a representative benchmark database of 20 cycloreversion reaction energies obtained by means of the high-level W1 thermochemical protocol. We use these benchmark values to assess the performance of a variety of contemporary DFT, double-hybrid DFT (DHDFT), standard ab initio, and compound thermochemistry methods. We show that this set of reaction energies provides an extremely challenging test for nearly all of the considered DFT and DHDFT methods. For example, about 80% of the considered functionals result in root-mean-square deviations (RMSDs) above 10 kJ mol^?1. The best DFT and DHDFT procedures are ωB97X and DSD-PBEP86-D3, with RMSDs of 4.7 and 7.9 kJ mol^?1, respectively. Coupled with the fact that the barrier heights for these reactions also pose a significant challenge for many DFT methods, this work shows that only a handful of functionals can quantitatively describe all aspects of the potential energy surface of this important class of reactions. In addition, this work shows that London dispersion effects are particularly large for this class of reactions. For example, empirical D3 dispersion corrections reduce the RMSDs for the DFT and DHDFT procedures by amounts ranging from 3.5 (PBE and B2K-PLYP) to 22.0 (BLYP) kJ mol^?1.     

Modeling absorption spectrum and saturation intensity of ZnO nano-colloid

In this work, the complex magnitude of the dielectric constant of a thin film of ZnO nano-particles has been obtained in the range of visible spectrum. Using this spectrum, the UV–visible absorptive spectrum of ZnO spherical nano-colloid is obtained using Mie theory. The absorption spectrum of ZnO nano-colloid has been related to the optical properties of the prepared thin film with a simulation model based on the Mie theory and the findings are corroborated by fitting with the experimental results. Based on this curve fitting, the volume fraction of nanoparticles in the nano-colloid is obtained and the diameter (and the Bohr radius) of the molecules contributing in a nanoparticle crystal structure has been obtained. In this paper, frequency dependence of the optical properties coefficients and also local field considerations are applied. Finally the precise magnitude of saturation intensity of ZnO nano-colloid is measured.