X‐ray investigations of bicyclic α‐methyl­ene‐δ‐valerolactones. II. (4aS,8aS)‐4a‐Methyl‐3‐methyl­eneper­hydro­chromen‐2‐one

The title compound, C₁₁H₁₆O₂, adopts a semifolded conformation with the δ‐lactone and cyclo­hexane rings almost perpendicular to one another. The β‐methyl substituent occupies an axial position with respect to the cyclo­hexane ring. The δ‐lactone moiety adopts a slightly distorted half‐chair arrangement, while the cyclo­hexane ring exists in an almost ideal chair conformation.     

Structurally tailored carbon xerogels produced through a sol–gel process in a water–methanol–inorganic salt solution

The impact of solvent composition as well as inorganic salt content and type on carbon xerogel structure was investigated. Carbon xerogels were derived from the sol–gel polycondensation of resorcinol with furfural in a water–methanol–inorganic salt solution. As inorganic salts, NaCl, NH₄ClO₄ and FeCl₃ were used. In order to conduct an accurate examination of the carbon xerogel structures and textures, inorganic salts were removed prior to carbonization. The xerogel structures can be tailored according to the water/methanol ratio and, to a lesser extent, according to the inorganic salt content and type in the starting solution. As a result, a significant amount of salt can be introduced to the gel network of the desired structure. The morphology and physical properties of the organic xerogels, carbon xerogels and their composites were characterized by means of SEM, N₂ sorption and XRD. It was found that samples derived from mixtures with FeCl₃ manifest well developed mesoporosity and depleated microporosity in comparison to samples prepared from mixtures with NaCl and NH₄ClO₄. Iron ions chemically bond to the xerogel matrix and cause its partial graphitization during the carbonization process, resulting in enhanced mesoporosity.     

Statically Admissible Stress Fields for Plastic Design of Connections of Steel Structures

ABSTRACT

The technique of statically admissible plastic stress fields is used in the plastic design of complex connections -of steel structures. An appropriate stress field gives a safe estimate of the shape of the connection design. Complex three-dimensional stress fields are composed of elementary subfields. Thus the procedure of plastic design consists in appropriate arrangement of subfields into a complex system of stresses.     

An Improved Synthesis of Dihalopyromellitic Acids

A practical molar scale syntheses of the commercially unavailable dichloro- and dibromopyromellitic acids are described in detail.     

Topotecan dynamics,tautomerism and reactivity—1H/13C NMR and ESI MS study

Topotecan (TPT) is in clinical use as an antitumor agent, hycamtin^?. Because of this, it requires both biologically and chemically useful information to be available. TPT acts by binding to the covalent complex formed by nicked DNA and topoisomerase I. This has a poisonous effect since inserted into the single‐strand nick and TPT inhibits its religation. We used NMR to trace TPT dynamics, tautomerism and solvolysis products in various solvents and conditions. Chemical stability was assessed in methanol and DMSO as compared to water, and the regioselectivity of the N‐ and O‐methylation was studied using various alkylating agents. The reaction products of quaternization of the nitrogen atom and methylation of the oxygen atom were characterized by means of ESI MS, ¹H/¹³C‐HMBC and ‐HSQCAD NMR. We have focused on the NMR characterization of TPT with an anticipation that its aggregation, tumbling properties and the intramolecular dipolar interactions will be a common feature for other compounds described in this article. These features can also be useful in tracing the interactions of this class of topoisomerase I (TopoI) poisons with DNA. Moreover, the results explained shed light on the recently disclosed problem of lack of stability of TPT in the heart tissue homogenate samples using the analytical assays developed for this class of compounds carried out in the presence of methanol. Copyright © 2010 John Wiley & Sons, Ltd.     

A Sharpened Nuclearity Condition and the Uniqueness of the Vacuum in QFT

It is shown that only one vacuum state can be prepared with a finite amount of energy and it appears, in particular, as a limit of physical states under large timelike translations in any theory which satisfies a phase space condition proposed in this work. This new criterion, related to the concept of additivity of energy over isolated subsystems, is verified in massive free field theory. The analysis entails very detailed results about the momentum transfer of local operators in this model.     

Intrinsic optical bistability for low-frequency rigid layer modes in MoS2 crystal

A study of the parametric optical excitation of overtones of rigid layer modes in a MoS₂ crystal is presented. This effect, resulting from the modulation of the vibrational frequency by a biharmonic optical field, is shown to lead to a significant intrinsic optical bistability, which can be registered in a four-wave mixing process.     

Conditions for blow-up of solutions of some nonlinear Volterra integral equations

In this paper we give necessary and sufficient conditions for blow-up of solutions for a particular class of nonlinear Volterra equations. We also give some examples.