Unsystematische Zinkchemie: zufällige Bildung und Struktur von Zn6(SC6F5)10(BPPAE)2

Non‐systematic Zinc Chemistry: Accidental Formation and Structure of Zn₆(SC₆F₅)₁₀(BPPAE)₂ The reaction between pyridine‐2‐carbaldehyde and ammonia‐contaminated zinc‐bis(pentafluorothiophenolate) yielded, beside the expected 1 : 1 adduct, small amounts of the hexanuclear cluster Zn₆(SC₆F₅)₁₀(BPPAE)₂. Its ligand BPPAE (1,2‐bis‐pyridine‐2‐yl‐2[(pyridine‐2‐ylmethylene)‐amino]‐ethenolate) results from condensation of three molecules of pyridine‐2‐carbaldehyde with one molecule of ammonia. The Zn₆ cluster consists of two centrosymmetrically arranged Zn₃ units which contain three differently coordinated zinc ions in ZnS₄, ZnS₂ON and ZnSON₃ environments.     

Towards validating a method for two-dimensional electrophoresis/silver staining

Two-dimensional electrophoresis (2-DE) is a technique involving numerous steps, many of them to be performed manually. Hence, some operator dependency must be taken into account. An attempt to elucidate the reliability of 2-DE combined with silver staining is presented, employing the general practice to validate a method in pharmaceutical analysis. Most proteomic studies employing 2-DE aim at qualitative or quantitative differences in protein expression. One of the most sensitive and broadly applied staining techniques is silver staining. In order to gain information on accuracy, precision, linearity, and ruggedness of this technique, gels were run in replicates with different amounts of protein from a complex standard sample. In addition, sets of gels were repeated by two different operators in a second independent laboratory equipped with identical hardware and software. Our results show that reliable qualitative data on differential protein expression can be obtained by 2-DE, nevertheless replicate gels should be run and experimental conditions have to be kept stringently to a standardized protocol. Quantitative data are just achievable with spots, which are well-resolved, of high quality, with an optical density (OD) above a certain threshold (OD > 10), and which show a linear response. Quantitative differences occurring due to method-derived deviations may easily be misinterpreted as true changes in protein expression. After normalization, relative standard deviation (RSD) values of approximately 30% (n = 4) could be obtained, therefore minor changes (< 50%) should be critically reviewed.     

On the Complexity of Partial Order Properties

The recognition complexity of ordered set properties is considered in terms of how many questions must be put to an adversary to decide if an unknown partial order has the prescribed property. We prove a lower bound of order n ² for properties that are characterized by forbidden substructures of fixed size. For the properties being connected, and having exactly k comparable pairs, k n ² / 4 we show that the recognition complexity is (n\choose 2). The complexity of interval orders is exactly (n\choose 2) - 1. We further establish bounds for being a lattice, being of height k and having width k.     

A domino ring-closing metathesis as a key-step in the synthesis of chiral lactones from d-mannitol

Chiral lactones were synthesized in six steps from d-mannitol. The key-step was a domino ring-closing metathesis reaction leading to the symmetric cleavage of a d-mannitol triene derivative and to the formation of two molecules of the desired lactone.