The Calf Intestinal Alkaline Phosphatase. II. Reaction between the metal content and the enzyme activity

Pure alkaline phosphatase (EC 3.1.3.1; 1500 U/mg) was dialyzed at 4° during 168 h against water, 10^?4M EDTA or 10^?4M o-phenanthroline. During the dialysis, samples were periodically removed and analyzed for metal content and activity. The results indicate that 1 mol of native calf intestinal alkaline phosphatase contains 4 g-atom of zinc and 4 g-atom of magnesium tightly bound, and that both metal ions are necessary for full enzyme activity. The dialyzed, partially demetallized enzyme could be reactivated by the addition of zinc and/or magnesium salts.     

Gas-chromatographischer Nachweis von Methylquecksilber im Vollblut im Nanogrammbereich

Ohne Zusammenfassung

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Detection of methylmercury in blood at the nanogram level by gas chromatography

     

X-ray absorption spectroscopy of liquid methanol microjets: bulk electronic structure and hydrogen bonding network

We have measured the X-ray absorption (XA) spectrum of liquid (298 K) methanol at the oxygen and carbon K edges. The 4a(1) orbital at the O K edge exhibits a pronounced sensitivity to the formation of intermolecular hydrogen bonds, with significant differences observed between the vapor and bulk spectra, whereas the C K edge reveals only subtle corresponding spectral changes. Comparison with DFT computed spectra of model methanol clusters indicates that the bulk liquid comprises long chains (n > 6) and rings of hydrogen-bonded monomers.     

Direct observation of the ionization step in solvolysis reactions: electrophilicity versus electrofugality of carbocations

Rates and equilibria of the reactions of highly stabilized amino-substituted benzhydrylium ions (Ar2CH+) with carboxylate ions have been determined photometrically in acetone and acetonitrile solutions. Treatment of covalent benzhydryl carboxylates (Ar2CH-O2CR) with aqueous acetone or acetonitrile leads to the regeneration of the colored amino-substituted benzhydrylium ions Ar2CH+, which do not undergo subsequent reactions with the solvent. One can, therefore, directly measure the first step of S(N)1 reactions. The electrofugality order, i.e., the relative ionization rates of benzhydryl esters Ar2CH-O2CR with the same anionic leaving group, does not correlate with the corresponding electrophilicity order, i.e., the relative reactivities of the corresponding benzhydrylium ions Ar2CH+ toward a common nucleophile. Thus, benzhydrylium ions which are produced with equal rates by ionization of the corresponding covalent esters may differ by more than 2 orders of magnitude in their reactivities toward nucleophiles, e.g., carboxylate ions. Variable intrinsic barriers account for the breakdown of the rate-equilibrium relationships. Complete free-energy profiles for the ionization of benzhydryl carboxylates Ar2CH-O2CR are constructed, which demonstrate that the transition states of these ionizations are not carbocation-like. As a consequence, variation of the solvent-ionizing power Y has only a small effect on the ionization rate constant (m = 0.35 to 0.55) indicating that small values of m in the Winstein-Grunwald equation do not necessarily imply an S(N)2 type mechanism.     

Experimental evidence for muonicX-rays from fission fragments

In the spectrum of muonic X-rays of²³⁸U measured in coincidence with prompt fission events a structure has been found which is attributed to 2p1s transitions of the muon attached to heavy fragments. The intensityI _s of this structure relative to the strengthI _pf observed for prompt fission has been determined to beI _s/I _pf=(6.0± 2.1) %. Although the experimental significance for the appeareance of this phenomenon is weak, this is the first experimental indication for its occuxence.We are indebted to the following institutes or organizations for financial support: Bundesministerium für Forschung und Technologie der Bundesrepublik Deutschland contract number 06BN271 (CR,PD,HH,FR,WS), Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organization of the Advancement of Pure Research (NWO) (JK,CTAMdL,AT), the Swiss National Foundation (SNF) (LAS,LS), and the Heinrich-Hertz-Foundation (HH) (FFK,BS).     

Counting statistics of collective photon transmissions

We theoretically study cooperative effects in the steady-state transmission of photons through a medium of N radiators. Using methods from quantum transport, we find a cross-over in scaling from N to N² in the current and to even higher powers of N in the higher cumulants of the photon counting statistics as a function of the tunable source occupation. The effect should be observable for atoms confined within a nano-cell with a pumped optical cavity as photon source.