Studies related to cephalosporins. Part 2 . Displacement reactions on 3-bromomethylcephems with salts of carboxylic acids

The reactivity of Δ³- and Δ²-3-bromomethylcephems toward carboxylate nucleophiles has been studied. The Δ³-bromomethylcephem 1 , less reactive than the Δ²-analogue 4 , is converted in high yields into 3-acyl-oxymethyl-3-cephems 2a-d , generally with no isomerization of the double bond, only within a narrow range of conditions. In particular, the Δ³-7-aminocephalosporanic acid (7-ACA) derivative 2a has been obtained as the only product in 91% yield by treatment of 1 with triethylammonium acetate in acetic acid. The Δ²-bromomethyl-cephem 4 is easily converted into the Δ²-acyloxymethyl-cepheras 5a-d without double bond isomerization, in very high yields.     

Simultaneous acquisition of X-ray spectra using a multi-wire, position-sensitive gas flow detector

A multi-wire, gas-filled position-sensitive detector has been developed for the simultaneous recording of wavelength-dispersed X-ray signals that enables X-ray fluorescence spectrometry with a limited multi-element capability in the low Z element range. Details of the modular construction of the detector are given. The detector performance was characterized using Al–K radiation and a variable slit system. The detector has been applied in a laboratory spectrometer equipped with an electron source and a double multilayer mirror device as the wavelength-dispersing element. Spectra from Al and Si obtained in the simultaneous acquisition mode show good agreement with calculations performed using a ray-tracing model.     

Acetone and perdeuterated acetone in UV-IMS

Measuring a mixture of acetone and perdeuterated acetone (acetone-d6) with an ultra-high resolution drift time ion mobility spectrometer (resolving power of R_p?=?235) and ultraviolet ionization (10.6 eV) at ambient pressure reveals three separated peaks. Two of the peaks can easily be associated with acetone and perdeuterated acetone. In a former publication several findings indicated an exchange of a methyl group and the formation of a H₃COCD₃ related peak. In this work the formed ion species were analyzed with a high resolution drift time ion mobility time of flight mass spectrometer. The mass spectra clearly show the formation of three proton-bound dimer peaks whereas the peak between acetone and acetone-d6 is a proton-bound mixed dimer consisting of one acetone and one acetone-d6 molecule.     

Many-to-many location-routing with inter-hub transport and multi-commodity pickup-and-delivery

In this paper, we consider a variant of the many-to-many location-routing problem, where hub facilities have to be located and customers with either pickup or delivery demands have to be combined in vehicle routes. In addition, several commodities and inter-hub transport processes are taken into account. A practical application of the problem can be found in the timber-trade industry, where companies provide their services using hub-and-spoke networks. We present a mixed-integer linear model for the problem and use CPLEX 12.4 to solve small-scale instances. Furthermore, a multi-start procedure based on a fix-and-optimize scheme and a genetic algorithm are introduced that efficiently construct promising solutions for medium- and large-scale instances. A computational performance analysis shows that the presented methods are suitable for practical application.     

Structural analysis of random propylene-ethylene copolymers

Structural properties of random propylene ethylene copolymers with low ethylene contents between 0 % and 11 mol % were investigated using mainly X-ray techniques. One of the essential issues of this paper is that a cocrystallization of the comonomer units does not take place. This is based on the following observations: The long period and the thickness of the crystalline lamellae decrease with increasing ethylene content. The electron density difference between crystalline and amorphous phase, however, as determined with the invariant, does not show any changes. The heat of fusion, normalized to the degree of crystallinity, does not decrease. This leads to the conclusion that the observed changes are not due to an incorporation of the ethylene units as defects, but to a reduced extension of the crystalline regions, now confined by the ethylene units which interrupt the helical chain conformation. The γ-modification, detectable by means of wide-angle X-ray diffractometry from an ethylene content of 5 mol % on, partially converted into the α-modification on annealing.     

Modifying LnHPDO3A Chelates for Improved T1 and CEST MRI Applications

The new ligand HPDO3MA [(R,R,R,R)-10-(2-hydroxypropyl)-α,α′,α′′-trimethyl-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid] was designed to combine and optimize the chemical properties of the macrocyclic ligands HPDO3A and DOTMA. The presence of the methyl groups on the acetic pendant arms of HPDO3A is expected to rigidify the structure of the ligand and favor an increase of the kinetic inertness of the Ln complexes. ¹H NMR spectra of Eu(HPDO3MA) displayed the presence of two pairs of diastereoisomers: SAP (square antiprismatic) and TSAP (twisted square antiprismatic) isomers (56 and 44 %, respectively). In addition, ¹H and ¹⁷O relaxometric NMR studies of Gd(HPDO3MA) showed approximately a 10 % increase in relaxivity and a faster water exchange rate with respect to Gd(HPDO3A). Moreover, a detailed chemical exchange saturation transfer (CEST) characterization of Yb(HPDO3MA) displayed a sensitivity about two times larger than that of Yb(HPDO3A) both in phantom and in cell labeling experiments. Finally, the kinetic inertness of Yb(HPDO3MA) was measured to be twice as high as that of Yb(HPDO3A), with a dissociation half-life at physiological pH of about 2500 years.