Charge density and experimental electrostatic potentials of two penicillin derivatives

Two penicillin derivatives, the active penamecillin and the inactive penamecillin-1beta-sulfoxide, were used to study the relationship between their charge density and their activity. Single crystals of both compounds were measured at the synchrotron beamline F1 at the HASYLAB/DESY, at 100 K and up to resolutions of around 0.4 A. Experimental charge densities were obtained by using the Hansen-Coppens multipole formalism. The cleavage of the amide bond in the beta-lactam ring is of paramount importance in the mechanism of action of penicillins. Topological analysis of this bond in terms of Bader's AIM theory showed that its strength is equal in both compounds; therefore a direct influence of bond strength on the activity can be ruled out. However, the two derivatives differ significantly in their experimental electrostatic potentials. These differences are discussed and provide further insight into the chemistry and activity of penicillins.     

Fine structure of hearing threshold and loudness perception

Hearing thresholds measured with high-frequency resolution show a quasiperiodic change in level called threshold fine structure (or microstructure). The effect of this fine structure on loudness perception over a range of stimulus levels was investigated in 12 subjects. Three different approaches were used. Individual hearing thresholds and equal loudness contours were measured in eight subjects using loudness-matching paradigms. In addition, the loudness growth of sinusoids was observed at frequencies associated with individual minima or maxima in the hearing threshold from five subjects using a loudness-matching paradigm. At low levels, loudness growth depended on the position of the test- or reference-tone frequency within the threshold fine structure. The slope of loudness growth differs by 0.2 dB/dB when an identical test tone is compared with two different reference tones, i.e., a difference in loudness growth of 2 dB per 10-dB change in stimulus. Finally, loudness growth was measured for the same five subjects using categorical loudness scaling as a direct-scaling technique with no reference tone instead of the loudness-matching procedures. Overall, an influence of hearing-threshold fine structure on loudness perception of sinusoids was observable for stimulus levels up to 40 dB SPL--independent of the procedure used. Possible implications of fine structure for loudness measurements and other psychoacoustic experiments, such as different compression within threshold minima and maxima, are discussed.     

Positron diffusion in metals

Calculations are presented of the positron diffusion constant, mobility and other diffusion related quantities in simple metals. The mobility is found to be largely limited by the positron-phonon interaction which is treated in the deformation potential model. The effect of positron conduction electron scattering is also evaluated and found to be small. The effect of positron impurity scattering is discussed and detailed estimates given for Li in Al. In dilute alloys at moderate temperatures the positron phonon interaction will dominate also over this effect.     

Uber die Einwirkung von Licht auf einige feste Salze vom Typus trans-[Co(en)2(NO2)(X)]Y

The influence of sunlight and particularly artificial light with wavelengths λ ≥ 430 nm on two groups of solid complex nitrocobalt(III) salts is investigated: (1) trans-isothiocyanatonitro-bis(ethylendiamine)cobalt(III)-perchlorate, -nitrate and -thiocyanate and (2) trans-chloronitro- and trans-nitratonitro-bis(ethylenediamine)cobalt(III)-nitrate. When the perchlorate of the first group is exposed to sunlight, its colour changes from yellow to red. This change is caused by a partial isomerization of the salt into the corresponding nitrito compound. Under the influence of artificial light with λ ≥ 430 nm the perchlorate and the nitrate of the first group change their colours in the way mentioned. The degree of isomerization under the same experimental conditions is 35 and 47% respectively. Neither the thiocyanate of the first group nor the chloronitronitrate of the second are influenced by the artificial light or sunlight. The absorbance curve of the irradiated nitratonitronitrate in aqueous solution is quite different from that of the non-irradiated. The corresponding nitratonitritonitrate has not been synthesized yet.     

Direct observation of the non-supported metal nanoparticle electron density of states by X-ray photoelectron spectroscopy

Synchrotron-based X-ray photoelectron spectroscopy on copper and silver cluster beams created by a magnetron-based gas-aggregation source has allowed mapping the electron density of states (DOS) of free metallic nanoparticles. The cluster DOS profiles obtained in the experiments strongly resemble the infinite solid DOS shapes, but the extracted cluster work-functions are lower than those for the bulk metal. The latter observation is explained by the initial negative charge on most of the clusters, created by the source.     

The reaction of indole and the indole grignard reagent with phosgene. A facile synthesis of indole-3-carboxylic acid derivatives

Indole-3-carboxylic acid (as well as indole-3-glyoxylic acid) derivatives are readily prepared from indoles (including oxindoles) and phosgene (oxalyl chloride), respectively. The interaction of these reagents with the indole Grignard reagent afforded several products including the cyclo-tetramers, 21 and 30 . Indolo-fused heterocycles can be readily prepared from the reaction of phosgene (or oxalyl chloride) with suitable reactants. Thus e.g., phosgene and 2-(2-hydroxy-phenyl)-N-methylindole readily gave 5,6-dihydro-11-methyl-6-oxobenzo[a]pyrano[4,3-b] indole ( 33 ).     

Invariom‐model refinement of l‐valinol

The structure of l ‐valinol [(S)‐(+)‐2‐amino‐3‐methyl­butan‐1‐ol or hydroxy­lated l ‐valine], C₅H₁₃NO, has been determined at 100 K by single‐crystal X‐ray diffraction. The independent atom model geometry, Flack parameter and figures of merit are compared with results from an invariom structure refinement. The latter provides H‐atom positions free of independent atom model bias and therefore yields a more accurate hydrogen‐bond pattern, and the geometry from invariom refinement shows an improved agreement with results from a quantum chemical geometry optimization.     

Separation of membrane proteins by two-dimensional electrophoresis using cationic rehydrated strips

Due to their poor solubility during IEF membrane proteins cannot be separated and analyzed satisfactorily with classical 2-DE. A more efficient method for such hydrophobic proteins is the benzyldimethyl-n-hexadecylammonium chloride (16-BAC)/SDS-PAGE, but the corresponding protocol is intricate and time-consuming. We now developed an easy-to-handle electrophoresis method in connection with a novel device which enables reproducible separation of ionic solubilized membrane proteins using individually rehydrated plastic sheet gel strips. These strips are suitable for the first dimension in a 2-D 16-BAC/SDS system and can be handled easily; this is demonstrated by the separation of membrane proteins of human embryonic kidney (HEK293) cells.     

Chemical Approach to Functional Artificial Opals

Artificial opals are self‐assembled colloidal crystals, which consist of a cubic dense packing (fcc) of hard (not film‐forming) colloids with diameters ranging from 200 to 900 nm. Because of their periodic nanostructure the assemblies are able to reflect light that matches their periodicity, i.e., UV‐ to IR‐radiation depending on the size of the colloids. Thus, they present a subgroup of ‘photonic crystals’. While, originally, the chemistry inside the colloids and the resulting opals was of minor significance, nowadays the chemical variation of opals is becoming more and more important for the preparation of functional and patterned opals. The search for functional opals is, therefore, especially focused on four topics: I) coloring agents, II) incorporation of fluorescent materials, III) replication, and IV) the controlled incorporation of defects.