Stark shift and broadening of FI and ClI lines

We report measured Stark shifts and widths of neutral flourine and chlorine lines. Wall stabilized arc is used as a plasma source. Electron densities 2–4×10²² m^?3 are determined from the width of theH _β line and electron temperatures 9500–10 000 K from plasma composition data. Experimental results for FI and ClI Stark widths and FI Stark shifts agree within 10% with semiclassical calculations. ClI Stark shifts are systematically smaller for about 20% than theoretical data with the only exception of the line from multiplet no. 15 where the discrepancy goes up to 49%. Results of investigation of similarities and regularities of Stark widths are in agreement with the study of Wiese and Konjevi?. Comparison of experimental Stark shifts shows certain types of regularities.     

On the properties of surfactant aqueous solutions

Summary From studies of aqueous solutions of dodecylammoniumnitrate an association mechanism has been proposed involving multiequilibrium. In the concentration range considered we can differentiate between two aspects: ranges of marked qualitative and quantitative changes and formation of differently structured surfactant species.

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Zusammenfassung Aus der Untersuchung wäßriger Lösungen von Dodecylammoniumnitrat würde ein Assoziationsmechanismus abgeleitet, welcher ein Multiequilibrium beinhaltet. Im untersuchten Konzentrationsbereich können zwei Bereiche unterschieden werden: Bereiche mit ausgeprägten qualitativen und quantitativen Änderungen und Bereiche mit der Bildung von verschieden strukturierten oberflächenaktiven Spezies.

     

Viskosimetrische Untersuchung des Systems LiNO3−H2O

Zusammenfassung Die Temperaturabhängigkeit der Viskosität im System LiNO₃–H₂O und im Temperaturbereich 20–70°C wird in der Gleichung =A expB/T=T ₀ zusammengefaßt; aus der so erhaltenen Beziehung werden Rückschlüsse auf die Struktur der Lösungen gezogen.

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Temperature dependence of the viscosity in the system LiNO₃–H₂O is expressed by =A expB/T-T ₀ in the temperature range 20–70°C. Possible relations to structural changes in the solutions are considered.

     

Global Forcing Number of Benzenoid Graphs

A global forcing set in a simple connected graph G with a perfect matching is any subset S of E(G) such that the restriction of the characteristic function of perfect matchings of G on S is an injection. The number of edges in a global forcing set of the smallest cardinality is called the global forcing number of G. In this paper we prove several results concerning global forcing sets and numbers of benzenoid graphs. In particular, we prove that all catacondensed benzenoids and catafused coronoids with n hexagons have the global forcing number equal to n, and that for pericondensed benzenoids the global forcing number is always strictly smaller than the number of hexagons.     

Can multivalency be expressed kinetically? The answer is yes

Inspired by the concept of multivalency and in pursuit of ever more intricate artificial molecular machines, we investigated the strict self-assembly of a triply threaded two-component superbundle, starting from a tritopic receptor in which three benzo[24]crown-8 macrorings are fused onto a triphenylene core and a trifurcated trication wherein three bipyridinium units are linked 1,3,5 to a central benzenoid core. The result of the investigation was quite unexpected and surprising. It transpired that the rapid formation of a doubly threaded two-component complex was followed by an extremely slow conversion (a week at 253 K in CD3COCD3 to reach equilibrium) of this kinetically controlled product into a thermodynamically controlled one, namely a triply threaded two-component superbundle. This intriguing observation begs the question: are there instances in nature where multivalency is expressed as a kinetically controlled process, prior to an equilibrium state being reached, and if so, what are the biological implications, if any?     

Double cyclisation of phenylglycine-o-carboxylic acids—I: New stable mesoionic oxazolones

Remarkably stable mesoionic oxazolones possessing an oxazolo[3,2-a]quinolinium structure (5a–b),8,16, 17) were obtained by the double cyclisation of phenylglycine-o-carboxylic acids (3a–c) in refluxing acetic anhydride or in benzoic anhydride at 140°, The 0-Ac group was eliminated to give the corresponding lactones (6a–b) or replaced by O-Ts (7). IR stretching vibrations of the endo-carbonyl were in the range 1710–1768 cm^?1, while v_1-CH exhibited unusually high values (3159–3194 cm^-1). 1-Acyl derivatives could be obtained only with TFAA (23–24), although easy deuteration of the same position took place in the presence of traces of trifluoroacetic acid. Hydrolysis of 5b led to the α-quinolone-N-acetic acid 27a. In the case of 5a, hydrolysis was accompanied by self-acylation of the nucleophilic site at C-4 with formation of a dimeric acid 28a. The presence of an additional Me group in phenylalanine-o-carboxylic acid (36) activates the corresponding mesoionic oxazolone 37 so that 1-acylation becomes possible with formation of the fused oxazole 38 by the Dakin-West reaction. Temperature dependent magnetic non-equivalence of methylene protons has been observed in acids 3b-d and f and also in the 7-membered anhydride 48b.     

Improvement of electron capture efficiency by resonant excitation

A novel pulse sequence improving the efficiency for electron capture dissociation (ECD) of an unmodified Fourier transform ion cyclotron resonance (FTICR) mass spectrometer by more than an order of magnitude is presented. Commercially available FTICR instruments are usually equipped with a filament-based electron source producing an electron beam that has a rather small cross section. An ideal overlap between the rotating ion cloud and the electron beam appears to be a prerequisite for a high ECD efficiency. A reduced interception of the ion cloud and the electron beam is probably due to the contribution of the magnetron motion to the trajectory of the ions, resulting in a precession about the z-axis of the instrument. By increasing the kinetic energy and therefore increasing the cyclotron radii of the precursor ions by resonant excitation, the overlap of the rotating ion cloud with the electron beam is improved. By use of this protocol the efficiency of electron capture is substantially increased and consequently the acquisition time of ECD spectra is reduced significantly. The capability of resonant excitation of the precursor ions during the irradiation with electrons is demonstrated for standard peptides. This approach is particularly valuable for analysis and characterization of O-glycosylated peptides. In addition to amino acid sequence information, the attachment site of the labile glycan moiety is determined, and also radical-site-induced fragmentations of the glycosidic bonds are observed.     

Development and prevalidation of a method for phenol determination by solid-phase spectrophotometry

A simple, sensitive and rapid solid-phase spectrophotometric procedure was developed for the determination of traces of phenol with 4-aminoantipyrine as a reagent (AAP-SPS), and the optimal experimental conditions were established. This method was performed by sorption and direct absorbance measurements of the product phenol-AAP sorbed on the anion-exchanger Dowex 1-X4 (0.2 g) at 495 nm (absorption maximum) and 700 nm (non-absorption wavelength). The sensitivity offered by the AAP-SPS procedure was higher by a factor of 40 compared with the respective conventional spectrophotometric method. Metrological characteristics were established using a prevalidation strategy. The AAP-SPS procedure is characterized by a linear calibration function in the working range of 0.05–0.50 μmol, low standard deviation of procedure (±0.012), low limit of determination (0.021 μmol), and favorable random (±0.85 to ±11.27%) and systematic deviations (−4.55 to +11.50%). Moreover, the accuracy of the system investigated by the recovery test is acceptable (99–102%). Favorable working and performance characteristics make the new SPS method ideal for phenol monitoring in pharmaceutical preparations as well as other matrices.     

Cyclic chronopotentiometry of nickel(II) at mercury electrodes in acidic perchlorate solutions: Case of higher order nonregenerative reactions following electron transfer

The reduction of Ni²⁺ ions at mercury electrodes in acidic perchlorate solutions, at perchlorate concentrations below 0.2 M, is characterized by absence of kinetic control in the preceding step, and by a complex reaction mechanism following the electron transfer. This reaction sequence is known to involve intermetallic compound formation between Ni and Hg and is best described, as shown here, by a parallel second and third order kinetic scheme. Apparent rate coefficients for this kinetic scheme were determined using cyclic chronopotentiometric data and fitting by digital simulation. A linearization test of computed kinetic rate coefficients versus the number of transitions permits quantitative tests of validity of assumptions made.     

Elektronenlokalisierung im Grundzustand und in angeregten Zuständen Pars-Orbital-Methode, 12. Mitt

UsingGleason's theorem the pars orbital concept is developed for excited states of conjugated systems described by CI-methods. A significance index is introduced to evaluate different patterns of fragmentation. The usefulness of this approach is illustrated for butadiene, biphenyl, naphthalene, and azulene.

11. Mitt.:H. Karpf, O. E. Polansky undM. Zander, Tetrahedron Lett.1978, 2069.