μ+ relaxation correlated with susceptibility in the van‐Vleck paramagnet PrIn3

A previously unobserved increase of the magnetic susceptibility in PrIn₃ at low temperatures is reported. The increase is shown to correlate nicely with a large increase in the transverse μSR depolarization rate. Evidence supports the conclusion that both phenomena are related to some degree of atomic disorder in the structure, and an associated strong Pr CEF level changes. This revised version was published online in July 2006 with corrections to the Cover Date.     

N-Alkyl thiocarbamoyl phosphonic acid esters—2 : Alkylation by methyl iodide accompanied by phosphonate dealkylation

Thiocarbamoyl phosphonates 1 did not react with alkylating agents to give the S-alkyl derivatives 2, but gave zwitterions 3a–e in which the phosphonate ester moiety was dealkylated. In some starting material could be recovered. A mechanism is suggested in order to explain the relationship between the alkylation and the dealkylation steps of the reaction.     

Optical activity of the background caused by sheep organ tissue extracts and its effect on spectrophotometric determination of the herbicide bentazone

Summary Nowadays mainly triazine herbicides are used for treating cultural plants against weeds. Many methods for their determination as well as for their extraction and purification have been developed, but the latter apply mainly for the determination in plant material. In the present publication the effect of the animal organ tissue extracts on the residue determination by optical methods is investigated. The background materials obtained after extraction of sheep muscle, liver, kidney, heart and lung with acetonitrile, acetone and hexane each are investigated by means of an infrared spectrometric method. Bentazone was chosen as the model pesticide and had been toxicologically tested with two experimental groups of sheep throughout three months administered with two different dose rates. Since the main chromophore of the bentazone molecule is represented by a ketonic group which is used for the spectrophotometric determination of the substance, the elimination of the background at the respective UV region should be based on suppression of the optic activity of equivalents of similar absorbing chromophores as owned by the bentazone molecule. For this reason the cleaning capacities of the Separcol SI C18, SI C1 and Carb of Czechoslovak provenience were examined. After elimination of interfering background bentazone determination was verified at a wavelength of 219 nm.     

Calixrotanes: Calixarenes Incorporating Spiro-Linked Cyclopropyl Groups

Macrocyclic compounds (calix[4]- and calix[6]arene derivatives) with aryl rings interconnected by spirocyclopropyl groups have been synthesized and structurally characterized. The compounds were prepared by the reaction of dichlorocarbene with calixarenes possessing exocyclic double bonds at the bridges, followed by reductive perdechlorination of the spirocyclopropyl groups. In all systems, pairs of geminal rings connected to the quaternary spiro carbon atoms are oriented anti, and the methylene groups of the cyclopropyl rings are located in isoclinal positions. Calix[6]rotane adopts in the crystal and in solution a 1,3,5-alternate conformation. The presence of the spirocyclopropyl groups increases the rigidity of the macrocyclic ring.     

Nanomaterial-based electrochemical sensors for detection of glucose and insulin

Journal of Solid State Electrochemistry - Electrochemical sensors for the detection of specific biomolecules have attracted a lot of interest over the recent years due to their high sensitivity,...     

A class of time-machine solutions with a compact vacuum core

We present a class of curved-spacetime vacuum solutions which develop closed timelike curves at some particular moment. We then use these vacuum solutions to construct a time-machine model. The causality violation occurs inside an empty torus, which constitutes the time-machine core. The matter field surrounding this empty torus satisfies the weak, dominant, and strong energy conditions. The model is regular, asymptotically flat, and topologically trivial. Stability remains the main open question.     

Structural investigation on hexasubstituted benzene derivatives. Part 2: The structure of metadinitrotetramethylbenzene and molecular mechanics analysis on meta and ortho derivatives

C₁₀H₁₂N₂O₄ (M r=224.2) crystallizes in the monoclinic system, space groupP2₁/mwitha=15.462(4),b=7.926(3),c=8.972(3) Å;=90.2(1)°;V=1099.5(6) ų;Z=4;D _c=1.35 gcm^–3;(Cu-K)=8.6 cm^–1; =1.5418 Å;F(000)=472. The position of the molecule on a crystallographic mirror plane forces the NO₂ plane to be normal to the benzene ring. The-electron-withdrawing character of the NO₂ groups induces a deformation on the geometry of the benzene.