Enantiomerically enriched atropisomeric N,N′-diaryl ureas by oxidative kinetic resolution of their 2-sulfanyl derivatives

Atropisomeric N-methyl-N,N′-diaryl ureas may be obtained in enantiomerically enriched form by oxidative kinetic resolution of their sulfide derivatives. The atropisomeric sulfides may be obtained in up to 97:3 er and display high stability to racemisation (half-lives at 25 °C of up to 500 years). Unlike related fully alkylated ureas, the product sulfoxides exhibit relatively weak thermodynamic conformational selectivity.     

Photocrystallographic structure determination of a new geometric isomer of [Ru(NH3)4(H2O)(eta1-OSO)][MeC6H4SO3]2

The structure of a new metastable geometric isomer of [Ru(NH3)4(H2O)(SO2)][MeC6H4SO3]2 in which the SO2 group is coordinated through a single oxygen in an eta1-OSO bonding mode has been determined at 13 K; the new isomer was obtained as a 36% component of the structure within a single crystal upon irradiation using a tungsten lamp.     

The determination of tin by carbon filament atomic absorption spectrometry

The atomic absorption characteristics of tin on a carbon filament atom reservoir are described. The behaviour of tin in aqueous solution astin(II) chloride, in xylene as tin octoate and in oil solutions is studied. The interferenceeffects of a selected range of seven cations, added as chlorides in aqueous solution or as naphthenates in non-aqueous media, and of sulphate and phosphate were examined. In all cases, the signals were measured in the filament reservoir with a surrounding hydrogen diffusion flame. The 1% absorption sensitivity in the organic media at the 286.3-nm line was 10^-10 g and 9·10^-11 g in aqueous solution. In the latter medium, the corresponding sensitivity at 224.6 nm was 6.7·10^-11 g. The linear analytical range lay in the region 0 to 20 ng.     

Hierarchical Decompositions and Circular Ray Shooting in Simple Polygons

A hierarchical decomposition of a simple polygon is introduced. The hierarchy has logarithmic depth, linear size, and its regions have at most three neighbors. Using this hierarchy, circular ray shooting queries in a simple polygon on n vertices can be answered in O(log² n) query time and O(n log n) space. If the radius of the circle is fixed, the query time can be improved to O(log n) and the space to O(n).     

A Telecommunications Project to Empower Kansas Elementary/Middle Level Teachers as Change Agents for Integrated Science and Mathematics Education

Nineteen elementary and 5 middle school in-service teachers served as regional lead teachers to provide 13 two- and four-day workshops for 235 in-service teachers. The lead teachers attended 100 hours of inservice training on national science/math reform curricula, cognitive theory, pedagogical strategies for enhancing problem solving, and authentic assessment procedures. The lead teachers then selected $30,000 worth of instructional materials for use in their classrooms. Subsequently, they developed four hands-on-manipulative-based workshops through extensive use of video-teleconferencing technology. The lead teachers strongly believe that this extensive project has made a permanent positive impact on the quality and quantity of integrated science and math instruction in Kansas.     

Cytochrome P450s: creating novel ligand sets

Cytochromes P450 are a ubiquitous group of hemoproteins that perform vital cellular reactions in all lifeforms. Until recently, it was thought that P450s contained non-covalently bound heme. However, it was established that covalent linkage of the heme macrocycle occurs naturally in one major group of the P450 superfamily. The reaction involves heme linkage to a conserved amino acid and is autocatalytic, occurring as a consequence of P450 turnover. This finding presents opportunities to engineer biotechnologically important P450s to covalently link the heme, in order to stabilize cofactor binding and to enhance operational stability of these P450s. This opportunity has been taken in studies on two important bacterial P450s and has produced variants with intriguingly different properties. In this article we survey the developments in the field, the relationships with heme macrocycle ligations in other proteins and the important impact that recent studies of heme ligation have had on our general appreciation of P450 structure and mechanism.