Zur Kinetik der Reaktion zwischen Thioharnstoff und Eisen(III)-Ionen

Kinetics have been investigated in the presence of excess thiourea. The existence of two intermediate complexes has been established; the results can be interpreted on the assumption of interaction of the thiourea molecules with these complexes.

---

---

Mit 4 Abbildungen     

A microwave and quantum chemical study of cyclopropaneselenol

The microwave spectrum of cyclopropaneselenol, C 3H 5SeH, has been investigated in the 21.9-80 GHz frequency range. The microwave spectra of the ground vibrational state of five isotopologues of cyclopropaneselenol (C 3H 5 (82)SeH, C 3H 5 (80)SeH, C 3H 5 (78)SeH, C 3H 5 (77)SeH, and C 3H 5 (76)SeH) of one conformer, as well as the spectra of two vibrationally excited states of each of the C 3H 5 (80)SeH and C 3H 5 (78)SeH isotopologues of this rotamer, have been assigned. The H-C-Se-H chain of atoms is synclinal in this conformer, and there is no indication of further rotameric forms in the microwave spectrum. The b-type transitions of the ground vibrational state of the more abundant species C 3H 5 (80)SeH and C 3H 5 (78)SeH were split into two components, which is assumed to arise from tunneling of the proton of the selenol group between two equivalent synclinal potential wells. The tunneling frequencies were 0.693(55) MHz for C 3H 5 (80)SeH and 0.608(71) MHz for C 3H 5 (78)SeH. The microwave study has been augmented by high-level density functional and ab initio quantum chemical calculations, which indicate that the H-C-Se-H dihedral angle is approximately 75 degrees from synperiplanar (0 degrees).     

Nanojets, electrospray, and ion field evaporation: molecular dynamics simulations and laboratory experiments

The energetics, interfacial properties, instabilities, and fragmentation patterns of electrosprays made from formamide salt solutions are investigated in a mass spectrometric vacuum electrospray experiment and using molecular dynamics (MD) simulations. The electrospray source is operated in a Taylor cone-jet mode, with the nanojet that forms being characterized by high surface-normal electric field strengths in the vicinity of 1 V/nm. Mass-to-charge ratios were determined for both positive and negative currents sprayed from NaI-formamide solutions with solute-solvent mole ratios of 1:8.4 and 1:36.9, and from KI-formamide solutions with mole ratios of 1:41 and 1:83. The molecular dynamics simulations were conducted on isolated 10 nm NaI-formamide droplets at mole ratios of 1:8 and 1:16. The droplet was subjected to a uniform electric field with strengths ranging between 0.5 and 1.5 V/nm. Both the experiments and simulations demonstrate a mixed charge emission regime where field-induced desorption of solvated ions and charged droplets occurs. The macroscopic parameters, such as average mass-to-charge ratio and maximum surface-normal field strengths deduced from the simulations are found to be in good agreement with the experimental work and consistent with electrohydrodynamic theory of cone-jets. The observed mass spectrometric Na (+) and I (-) solvated ion distributions are consistent with a thermal evaporation process, and are correctly reproduced by the simulation after incorporation of the different flight times and unimolecular ion dissociation rates in the analysis. Alignment of formamide dipoles and field-induced reorganization of the positive and negative ionic charges in the interfacial region are both found to contribute to the surface-normal field near the points of charge emission. In the simulations the majority of cluster ions are found to be emitted from the tip of the jet rather than from the neck region next to the Taylor cone. This finding is consistent with the experimental energy distributions of the solvated ions which demonstrate that indeed most ions are emitted closer to the jet region, that is, beyond the cone-neck region where ohmic losses occur. This observation is also consistent with continuum electrohydrodynamic predictions of cluster-ion evaporation at surface regions of high curvature and therefore maximum surface electric field strengths, which may be the cone-neck region, the breakup region of the jet (usually near the tip of the jet), or the emitted charged droplets. In the nanoscale jets observed in this study, the regions of highest spatial curvature are at the ends of the jets where nascent drops either are forming or have just detached.     

A microwave and quantum chemical study of cyclopropanethiol

The microwave spectra of cyclopropanethiol, C(3)H(5)SH, and one deuterated species C(3)H(5)SD, have been investigated in the 20 - 80 GHz frequency range. The spectra of the ground vibrational state and of three vibrationally excited states of the parent species of a conformer which has a synclinal ("gauche") arrangement for the H-C-S-H chain of atoms, was assigned. The H-C-S-H dihedral angle is 76(5)° from synperiplanar (0°). The b-type transitions of the ground and of the vibrationally excited states of the parent species were split into two components, which is assumed to arise from tunneling of the proton of the thiol group between two equivalent synclinal potential wells. No splitting was resolved in the spectrum of C(3)H(5)SD. The tunneling frequency of the ground vibrational state of C(3)H(5)SH is 1.664(22) MHz. The tunneling frequency of the first excited-state of the C-S torsion is 52.330(44) MHz, whereas this frequency is 26.43(13) and 3.286(61) MHz, respectively, for the first excited states of the two lowest bending vibrations. The dipole moment of the ground vibrational state of the parent species is μ(a) = 4.09(5), μ(b) = 2.83(11), μ(c) = 0.89(32), and μ(tot) = 5.06(16) × 10(-30) C m. The microwave study has been augmented by high-level density functional and ab initio quantum chemical calculations.     

A microwave spectroscopic and quantum chemical study of propa-1,2-dienyl selenocyanate (H(2)==C==CHSeC[triple bond]N) and cyclopropyl selenocyanate (C(3)H(5)SeC[triple bond]N)

The microwave spectra of propa-1,2-dienyl selenocyanate, H(2)C==C==CHSeC[triple bond]N, and cyclopropyl selenocyanate, C(3)H(5)SeC[triple bond]N, are reported. The spectra of the ground and two vibrationally excited states of the (80)Se isotopologue and the spectrum of the ground state of the (78)Se isotopologue were assigned for one rotameric form of H(2)C==C[double bond, length as m-dash]CHSeC[triple bond]N. This conformer is characterized by a C-C-Se-C dihedral angle of 129(5) degrees from synperiplanar (0 degrees ) and is shown to be the global minimum of H(2)C[double bond, length as m-dash]C[double bond, length as m-dash]CHSeC[triple bond]N. The spectra of the ground and of three vibrationally excited states of the (80)Se isotopologue, as well as of the ground state of the (78)Se isotopologue of one rotamer of C(3)H(5)SeC[triple bond]N were assigned. This conformer has a H-C-Se-C dihedral angle of 80(4) degrees from synperiplanar and is at least 3 kJ mol(-1) more stable than any other form of the molecule. The microwave study has been augmented by quantum chemical calculations at the B3LYP/6-311+ +G(3df,3pd) and MP2/6-311+ +G(3df,3pd) levels of theory.     

Variability in different antimony,arsenic and chromium species in waters and bottom sediments of three water reservoirs in Upper Silesia (Poland): a comparative study

Migration of metals/metalloids and their inorganic forms from bottom sediments into waters and from waters into bottom sediments is a complex process. Understanding this mechanism is essential for recognising transformations that occur in water reservoir ecosystems. The following research was conducted in 2012–2014. The aim was to define the time and spatial correlations in the changes of total and ionic antimony, arsenic and chromium concentrations in waters and bottom sediments of three water reservoirs located in Upper Silesia (Poland), i.e. P?awniowice, Rybnik and Gocza?kowice. The ionic form contents were determined with high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS). The research was carried out to verify whether the bottom sediments deposited in the discussed reservoirs could have posed an environmental threat due to the possible release of toxic ionic forms (i.e. As(III), Sb(III) and Cr(VI)) into the pelagic zone. The comparison of the research results obtained for three reservoirs (being under different anthropopressure influence) enabled the researchers to describe the bioavailability of specific elements and their species. It also helped to discern the existing environmental threats for such water reservoirs and their users.     

Towards the classification of self-dual bent functions in eight variables

In this paper, we classify quadratic and cubic self-dual bent functions in eight variables with the help of computers. There are exactly four and 45 non-equivalent self-dual bent functions of degree two and three, respectively. This result is achieved by enumerating all eigenvectors with ± 1 entries of the Sylvester Hadamard matrix with an integer programming algorithm based on lattice basis reduction. The search space has been reduced by breaking the symmetry of the problem with the help of additional constraints. The final number of non-isomorphic self-dual bent functions has been determined by exploiting that EA-equivalence of Boolean functions is related to the equivalence of linear codes.     

Simultaneous determination of fluoride and monofluorophosphate in toothpastes by supressed ion chromatography

Suppressed ion chromatography with a highly selective and high capacity anion-exchange column is used for the determination of anionic compounds in ten commercially available toothpastes. Minimal sample preparation is needed, requiring only dilution and filtration over a solid-phase extraction cartridge. Quantitative analysis of fluoride and monofluorophosphate, as well as chloride, nitrate, orthophosphate, and sulfate is achieved in one chromatographic run with a total analysis time of 25 minutes. Optimized analytical conditions are validated in terms of accuracy, precision, and total uncertainty, and the results demonstrate the reproducibility of ion chromatography. The coefficient of determination for the anions ranges from 0.9896 to 0.9997. The spiked recoveries for the anions are 88–108%. The change in the fluoride content of the toothpaste with storage time is investigated.