Cysteamine and its homoleptic complexes with group 12 metal ions. Differences in the coordination chemistry of ZnII, CdII, and HgII with a small N,S-donor ligand

2-Ammoniumethanethiolate, (-)SCH(2)CH(2)NH(3)(+), the first structurally characterized zwitterionic ammoniumthiolate, is the stable form of cysteamine (HL) in the solid state and in aqueous solution. Reactions of ZnCl(2), Cd(Oac)(2), and HgCl(2) with cysteamine and NaOH in a 1:2:2 ratio, respectively, lead to the homoleptic complexes ML(2). Their single-crystal X-ray structures demonstrate basic differences in the coordination chemistry of Zn(II), Cd(II), and Hg(II). While chelating N,S-coordination modes are found for all metal ions, Zn(II) forms a mononuclear complex with a distorted tetrahedral Zn(N(2)S(2)) coordination mode, whereas Hg(II) displays a dimer with Hg(N(2)S(2)) coordinated monomers being connected by two long Hg...S contacts. Solid-state (199)Hg NMR spectra of HgL(2) and [Hg(HL)(2)]Cl(2) reveal a low-field shift of the signals with increasing coordination number. Strong and nearly symmetric Cd-S-Cd bridges in solid CdL(2) lead to a chain structure, Cd(II) displaying a distorted square pyramidal Cd(N(2)S(3)) coordination mode. The ab initio [MP2/LANL2DZ(d,f)] structures of isolated ML(2) show a change from a distorted tetrahedral to bisphenoidal coordination mode in the sequence Zn(II)-Cd(II)-Hg(II). A natural bond orbital analysis showed a high ionic character for the M-S bonds and suggests that the S-M-S fragment is best described by a 3c4e bond. The strength of the M...N interactions and the stability of ML(2) toward decomposition to M and L-L decreases in the sequence Zn > Cd > Hg. Ab initio calculations further suggest that a tetrahedral S-M-S angle stabilizes Zn(II) against substitution by Cd(II) and Hg(II) in a M(N(2)S(2)) environment. Such geometry is provided in zinc-finger proteins, as was found by a database survey.     

Ueber die Bestimmung von Weins?ure und Citronens?ure bei Gegenwart verschiedener Basen und S?uren

Ohne Zusammenfassung     

Selective alignment of molecular spin isomers

We experimentally demonstrate field-free, spin-selective alignment of ortho- and para molecular spin isomers at room temperature. By means of two nonresonant, strong, properly delayed femtosecond pulses within a four wave mixing arrangement, we observed selective alignment for homonuclear diatomics composed of spin 1/2 (15N) or spin 1 (14N) atoms. The achieved selective control of the isomers' angular distribution and rotational excitation may find applications to analysis, enrichment, and actual physical separation of molecular spin modifications.     

Microprobe sampling—Photo ionization-time-of-flight mass spectrometry for in situ chemical analysis of pyrolysis and combustion gases: Examination of the thermo-chemical processes within a burning cigarette

A microprobe sampling device (μ-probe) has been developed for in situ on-line photo ionization mass spectrometric analysis of volatile chemical species formed within objects consisting of organic matter during thermal processing. With this approach the chemical signature occurring during heating, pyrolysis, combustion, roasting and charring of organic material within burning objects such as burning fuel particles (e.g., biomass or coal pieces), lit cigarettes or thermally processed food products (e.g., roasting of coffee beans) can be investigated. Due to its dynamic changes between combustion and pyrolysis phases the cigarette smoking process is particularly interesting and has been chosen as first application. For this investigation the tip of the μ-probe is inserted directly into the tobacco rod and volatile organic compounds from inside the burning cigarette are extracted and real-time analyzed as the glowing front (or coal) approaches and passes the μ-probe sampling position. The combination of micro-sampling with photo ionization time-of-flight mass spectrometry (PI-TOFMS) allows on-line intrapuff-resolved analysis of species formation inside a burning cigarette. Monitoring volatile smoke compounds during cigarette puffing and smoldering cycles in this way provides unparalleled insights into formation mechanisms and their time-dependent change. Using this technique the changes from pyrolysis conditions to combustion conditions inside the coal of a cigarette could be observed directly. A comparative analysis of species formation within a burning Kentucky 2R4F reference cigarette with μ-probe analysis reveals different patterns and behaviors for nicotine, and a range of semi-volatile aromatic and aliphatic species.     

The $ B\to\pi K$ puzzle and its relation to rare B and K decays

The standard-model interpretation of the ratios of charged and neutral rates, R _c and R _n, respectively, points towards a puzzling picture. Since these observables are affected significantly by colour-allowed electroweak (EW) penguins, this puzzle could be a manifestation of new physics in the EW penguin sector. Performing the analysis in the R _n- R _c plane, which is very suitable for monitoring various effects, we demonstrate that we may, in fact, move straightforwardly to the experimental region in this plane through an enhancement of the relevant EW penguin parameter q. We derive analytical bounds for q in terms of a quantity L, which measures the violation of the Lipkin sum rule, and point out that strong phases around are favoured by the data, in contrast to QCD factorisation. The modes imply a correlation between q and the angle that, in the limit of negligible rescattering effects and colour-suppressed EW penguins, depends only on the value of L. Concentrating on a minimal flavour-violating new-physics scenario with enhanced Z ⁰ penguins, we find that the current experimental values on require roughly . As the data give , L has either to move to smaller values once the data improve or new sources of flavour and CP violation are needed. In turn, the enhanced values of L seen in the data could be accompanied by enhanced branching ratios for the rare decays , , and . Most interesting turns out to be the correlation between the modes and , with the latter depending approximately on a single scaling variable .Received: 8 September 2003, Published online: 12 November 2003     

B-->pipi, new physics in B-->piK, and implications for rare K and B decays

The measured B-->pipi,piK branching ratios (BRs) exhibit puzzling patterns. We point out that the B-->pipi hierarchy can be nicely accommodated in the standard model (SM) through nonfactorizable hadronic interference effects, whereas the B-->piK system may indicate new physics (NP) in the electroweak (EW) penguin sector. Using the B-->pipi data and the SU(3) flavor symmetry, we fix the hadronic B-->piK parameters and show that any currently observed feature of the B-->piK system can be easily explained through enhanced EW penguin diagrams with a large CP-violating NP phase. This in turn implies in particular an enhancement of the K(L)-->pi(0)nunu rate by 1 order of magnitude, with BR(K(L)-->pi(0)nunu) approximately 4BR(K+-->pi(+)nunu), BR(K(L)-->pi(0)e(+)e(-))=O(10(-10)), and (sin(2beta)(pinunu)<0. We address also other rare K and B decays and B(d)-->phiK(S).     

One-loop photonic corrections to Bhabha scattering in d=4-2ε dimensions

The luminosity measurement at the projected International Linear e⁺e^- Collider ILC is planned to be performed with forward Bhabha scattering with an accuracy of the order of 10^-4. A theoretical prediction of the differential cross-section has to include one-loop weak corrections, with leading higher order terms, and the complete two-loop QED corrections. Here, we present the weak part and the virtual one-loop photonic corrections. For the photonic corrections, the expansions in ε=(4-d)/2 are derived with inclusion of the terms of order ε in order to match the two-loop accuracy. For the photonic box master integral in d dimensions we compare several different methods of evaluation.