Refraktometrie zur Untersuchung von Fruchts?ften

Ohne Zusammenfassung     

Structure and dynamics of Au+ ion in aqueous solution: ab initio QM/MM MD simulations

Structure and dynamics of hydrated Au(+) have been investigated by means of molecular dynamics simulations based on ab initio quantum mechanical molecular mechanical forces at Hartree-Fock level for the treatment of the first hydration shell. The outer region of the system was described using a newly constructed classical three-body corrected potential. The structure was evaluated in terms of radial and angular distribution functions and coordination number distributions. Water exchange processes between coordination shells and bulk indicate a very labile structure of the first hydration shell whose average coordination number of 4.7 is a mixture of 3-, 4-, 5-, 6-, and 7-coordinated species. Fast water exchange reactions between first and second hydration shell occur, and the second hydration shell is exceptionally large. Therefore, the mean residence time of water molecules in the first hydration shell (5.6 ps/7.5 ps for t*= 0.5 ps/2.0 ps) is shorter than that in the second shell (9.4 ps/21.2 ps for t*= 0.5 ps/2.0 ps), leading to a quite specific picture of a "structure-breaking" effect.     

Do the interstellar molecules CCCO and CCCS rearrange when energised?

Neutrals CCCO, CC(13)CO, CCCS and CC(13)CS have been prepared by one-electron vertical (Franck-Condon) oxidation of the precursor anion radicals (CCCO)(-*), (CC(13)CO)(-*), (CCCS)(-*) and (CC(13)CS)(-*)respectively in collision cells of a reverse sector mass spectrometer. Ionisation of the neutrals to decomposing cations shows the neutrals to be stable for the microsecond duration of the neutralisation-ionisation ((-)NR(+)) experiment. No rearrangement of the label in energised CC(13)CO or CC(13)CS occurs during these experiments. In contrast, minor rearrangement of (CC(13)CO)(+*) is observed [(CC(13)CO)(+*)-->(OCC(13)C)(+*), while significant rearrangement occurs for (CC(13)CS)(+*) [(CC(13)CS)(+*)-->(SCC(13)C)(+*)]. Theoretical calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory show that the cationic rearrangements occur by stepwise processes via key rhombic structures. Overall, the degenerate processes result in O and S migration from C-3 to C-1. The cations (CCCO)(+*) and (CCCS)(+*) require excess energies of > or = 516 and > or = 226 kJ mol(-1) respectively to effect rearrangement.     

Enantioselective synthesis of the [6,6] spiroketal core of reveromycin A

[structure: see text] Reveromycin A (1) belongs to a family of microbial polyketides with unusual structural features and biological activities. The structure of 1 is composed of a [6,6] spiroketal core decorated with highly unsaturated side chains. As a prelude to the synthesis of 1, we present herein a short, efficient, and enantioselective synthesis of the C9-C21 fragment 5 (spiroketal core) of reveromycin A.     

The electromagnetic properties of blends of poly(p‐phenylene‐vinylene) derivatives

We report the studies on the frequency dependence of the complex permittivity, and on the electromagnetic interference (EMI) shielding of conductive blends. The blends were obtained from conjugated oligomers of (p‐phenylene‐1,3,5‐hexatrienylene) end‐capped by Schiff base units and dispersed in an insulating matrix of poly(vinyl chloride) (PVC) and doped with sulfuric acid, H₂SO₄. Permittivity measurements from 10 kHz to 10 GHz have pointed out that the electrical conductivity of composites were in a range 10⁻⁵–10⁺¹ S/cm. From these experimental data performed on 250–500 µm, the reflectivity coefficients [R(dB)] have been calculated for simulation of mm thick samples, they have values of −9 to −20 dB depending on the frequency and on the thickness of the composites. These permitivity data have also allowed us to develop modelization of the radioelectric properties of conductive blends, using McLachlan's General Effective Medium (GEM) Theory. The optimization of the GEM parameters suggests some informations about the shape of the particles as well as the micro/macrostructure of the composite materials. Copyright © 2000 John Wiley & Sons, Ltd.     

The isomeric ratios in photonuclear reactions of natural barium induced by bremsstrahlungs with endpoint energies in the giant dipole resonance region

We have determined the isomeric ratios in ¹³⁰Ba(γ, n)^129m,gBa, ¹³²Ba(γ, n)^131m,gBa and ¹³⁴Ba(γ, n)^133m,gBa photonuclear reactions of natural barium induced by bremsstrahlungs with end-point energies in the giant dipole resonance region. The investigated samples were irradiated at electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reaction, Joint Institute for Nuclear Research, Dubna, Russia. The gamma spectra of the samples irradiated were measured with spectroscopic system consisting of 8192 channel analyzer and high-energy resolution (180 keV at gamma ray 1332 keV of ⁶⁰Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors.     

Fabrication and proton conductivity of sulfonated silica composites prepared by postoxidization of mercaptomethoxysilane

Sol–gel derived organic–inorganic hybrids containing phosphotungstic acid (PWA) have been prepared previously to obtain proton conductive membranes. However, leaking of PWA was a serious problem to achieve the higher proton conductivity. In this study, polyelectrolyte membranes functionalized with sulfonic acid groups were fabricated by the sol–gel method. Proton conductivity measurements were performed on an impedance analyzer at 80°C/95% RH. The functionalized polyelectrolyte membranes exhibited the proton conductivity σ ～ 0.9 (S/cm) which was much higher than the previously reported hybrids containing PWA. Although the hybrids exhibited fairly high proton conductivity irrespective to the catalysts used, that under the low relative humidity strongly depends on the catalysts. Among the hybrids prepared in this study, the membrane synthesized with HCl showed outstanding proton conductive properties even at the low humidity thanks to the proton transport channel formed by the swelling of ionic clusters. This fact was confirmed by measuring the ion exchange capacity, water uptake, swelling rate, Fourier transform infrared spectroscopy, atomic force microscopy, and thermogravimetric analysis. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Friedel–Crafts acylation using bismuth triflate in [BMI][PF6]

Bismuth trifluoromethanesulfonate was found to be a good catalyst for the Friedel–Crafts acylation. Bismuth triflate immobilized in an ionic liquid was the most efficient catalytic system. Bismuth triflate in [BMI][PF₆] catalyzes this reaction under microwave irradiation allowing the rapid synthesis of aryl ketones in excellent yields. The catalyst system was easily recovered and reused several times.     

Highly sensitive and rapid determination of sunset yellow in drinks using a low-cost carbon material-based electrochemical sensor

Starting from simple graphite flakes, an electrochemical sensor for sunset yellow monitoring is developed by using a very simple and effective strategy. The direct electrochemical reduction of a suspension of exfoliated graphene oxide (GO) onto a glassy carbon electrode (GCE) surface leads to the electrodeposition of electrochemically reduced oxide at the surface, obtaining GCE/ERGO-modified electrodes. They are characterized by cyclic voltammetry (CV) measurements and field emission scanning electron spectroscopy (FE-SEM). The GCE/ERGO electrode has a high electrochemically active surface allowing efficient adsorption of SY. Using differential pulse voltammetry (DPV) technique with only 2 min accumulation, the GCE/ERGO sensor exhibits good performance to SY detection with a good linear calibration for concentration range varying 50–1000 nM (R² = 0.996) and limit of detection (LOD) estimated to 19.2 nM (equivalent to 8.9 μg L⁻¹). The developed sensor possesses a very high sensitivity of 9 μA/μM while fabricated with only one component. This electrochemical sensor also displays a good reliability with RSD value of 2.13% (n = 7) and excellent reusability (signal response change < 3.5% after 6 measuring/cleaning cycles). The GCE/ERGO demonstrates a successful practical application for determination of sunset yellow in commercial soft drinks.

Graphical abstract

     

One-pot synthesis of a novel magnetic activated carbon/clay composite for removal of heavy metals from aqueous solution

Abstract

In the present work, a novel composite consisting of magnetite, activated carbon from spent coffee grounds and natural clay (MACCC) was prepared by a one-pot synthesis method via a simultaneous activation and magnetization processes. Various techniques (XRD, FTIR, SEM, TEM, EDX, BET) were utilized to characterize the synthesized composite before utilizing it as an adsorbent for removal of Cu(II), Ni(II) and Pb(II) ions from aqueous solutions. Conditions for removal of heavy metals were thoroughly optimized as 25?°C, pH of 5.5, adsorbent dosage of 2?g L^?1, and a contact time of 60?min. Three models of pseudo first-, second-order and intraparticle diffusion as well as three models of Langmuir, Freundlich, and Temkin were used to analyze kinetics and isotherms of the adsorption process. Thermodynamics was discussed completely. Regeneration and recyclability of the adsorbent were also evaluated. Based on the analysis of experimental results, a possible adsorption mechanism of heavy metals onto the synthesized composite was proposed. The maximum capacities caculated from Langmuir model followed the order of Pb(II) > Cu(II) > Ni(II) as 143.56, 96.16 and 84.86?mg·g^?1, respectively. The overall results indicated that MACCC is a potential adsorbent for removal of toxic Pb(II), Cu(II) and Ni(II) ions from wastewater due to simple preparation, high removal efficiency and good recyclability.