Intermolecular alkyl/aryl exchange of 2-iminothiazoles with isothiocyanates and isocyanates: scopes and limitations

2-Iminothiazole, an isoform of 2-aminothiazole, is a scaffold of synthetic and medicinal significance. We have reported an efficient method by which alkyl group of 2-alkyliminothiazoles is changed into other alkyl groups by isothiocyanates. In this article, a detailed mechanistic aspect, and the scopes and limitations were disclosed. All the reactions were carried out in toluene at 105 °C without any additive. The reaction is a reversible process and the equilibrium is determined by the reactivity of both reactants, in which the more electron-withdrawing alkyl or aryl groups at the 2-imino group or isothiocyanate showed higher reactivities. With this simple method, we effectively altered the alkyl group attached on the imine nitrogen. A synthetic problem in 2-iminothiazole chemistry, synthesis of amino acid-derived 2-iminothiazole was solved in a very simple manner. Using suitably designed 2-iminothiazole substrate, the electrophilic reactivity of various isothiocyanates could be empirically compared by this exchange reaction. Moreover, successful exchange reaction using isocyanates instead of isothiocyanates broadened the utility of this reaction.     

Variational dimension of random sequences and its application

A concept of variational dimension is introduced for a random sequence with stationary increments. In the Gaussian case, the variational dimension in the limit coincides with the Hausdorff dimension of a proper random process. Applications of the concept are illustrated by examples of neurological data and network traffic analysis.     

Evidence for an Equilibrium between an N-heterocyclic Carbene and Its Dimer in Solution

Evidence for the Wanzlick equilibrium between carbene 1 and dibenzotetraazafulvalene (1)(2) at ambient temperature has been found (see scheme). Enetetramines of type (1)(2) can also be cleaved by coordinatively unsaturated transition metal compounds to form dicarbene complexes.     

Detection of myocardial viability by low-dose dobutamine Cine MR imaging

The purpose of this work was to test the diagnostic value of dobutamine stress magnetic resonance imaging (MRI) for predicting recovery of regional myocardial contractility after revascularization. Cardiac wall motion abnormalities are due to either non-viable and/or scarred, or viable, but hibernating, myocardial tissue. Dobutamine stress leads to increased systolic wall thickening only in viable myocardium. Twenty-five patients with akinetic or dyskinetic myocardial regions were examined with a Cine FLASH-2D sequence at rest and during dobutamine stress (10 μg/kg/min). Patients were re-examined at rest 3, and in case of persisting wall motion defects, 6 months after revascularization. Criterion of viability was increasing end-systolic wall thickening during stress and/or at follow-up. Akinetic regions related either to the LAD (n = 19) or to the RCA (n = 6) were judged viable if >=50% of the affected segments improved. MR studies were completed in all subjects without arrhythmia or need for early terminations due to symptoms. Sensitivity, specificity, and positive predictive value for the prediction of myocardial viability were 61%, 90%, and 87% for the segment-related analysis, and 76%, 100%, and 100% for the patient-related analysis based on coronary artery distribution, respectively. Dobutamine stress MRI allows to predict global functional recovery of akinetic myocardial regions after revascularization with a high positive predictive value and high specificity.     

Zur Lumineszenz des Zinkoxyds

The temperature dependance of efficiency and decay of the ultraviolet and green luminescence bands at UV- and cathode ray-excitation is investigated. In addition to earlier results the Riehl-effect is only observed when excited by cathode rays. The UV-band decays hyperbolically at all temperatures while the decay of the green band depends on kind and intensity of the excitation as well as on temperature. The results can be interpreted by considering the increasing number of electrons in the conduction band under different kinds of excitation and the variation of conductivity with temperature. Furthermore, the glow curves of various ZnO-samples (untreated and annealed in reducing atmosphere) show one or two peaks respectively, thus revealing two trap depths. As the light sum increases with the efficiency it is assumed that by reduction both activators and traps are created. The occurrence of thermoluminescence with many conduction electrons being present leads to the assumption of hole traps.     

Vergleichbare Kraftfelder vieratomiger Formylverbindungen

Comparable force fields for HCOO^–, HFCO, HClCO and HDCO have been calculated on the basis of internal coordinates. Linear relations between (i) the carbonyl bond order and the carbonyl stretching force constant, (ii) the sum of the three in-plane bending force constants and the hydrogen out-of-plane force constantf , (iii) a combination of orbital electronegativities andf , have been obtained. The observed in-plane vibrational frequencies have been calculated with an average error of 6.3 cm^–1 or 0.4%.

     

New aspects of the luminescence of magnesiumtitanate part I: Activation with chromium

Mg₂TiO₄:Cr³⁺ annealed at 560°C shows luminescence properties which differ considerably from those of the unannealed phosphor used so far. In both cases the regular Cr³⁺ ions only absorb the irradiated energy transferring it radiationless to the real luminescence centres, but the annealed phosphor reveals a new spectrum consisting of a few sharp lines. The radiance of the single lines can be influenced by powdering, which in connection with the annealing effect shows that the centres of both types of phosphors consist of clusters of lattice defects and octahedrally coordinated Cr³⁺ ions. These clusters or associates form themselves by thermal diffusion during the annealing process. Furthermore criteria have been found showing that the R lines do not come from only one but from two Cr³⁺ ions situated in non-equivalent lattice sites.