Optimization of Sr-90 precipitation in nitric acid using design of experiments for radioactive waste characterization method

Journal of Radioanalytical and Nuclear Chemistry - 90Sr radiochemical method using nitric acid for Sr and Ca separation was optimized using design of experiments methodology. Nitric acid...     

Quantification of curium isotopes in environmental samples: drawbacks,speciation and specific tracer

Journal of Radioanalytical and Nuclear Chemistry - In this study, drawbacks of the use of 243Am as a tracer in order to quantify curium isotopes during a complex chemical procedure were...     

Oxidation of alcohols by electrochemically regenerated nickel oxide hydroxide. Selective oxidation of hydroxysteroids

Primary alcohols, α,ω-diols and secondary alcohols are easily transformed into carboxylic acids, dicarboxylic acids or ketones, respectively, by heterogeneous oxidation with nickel oxide hydroxide electrochemically regenerated at a nickel hydroxyde electrode. The results are discussed in comparison to those of the nickel peroxide and chromic acid oxidation. The oxidation rate decreases with increasing steric hindrance of the alcohol, thus allowing the selective oxidation of the 3-position in hydroxysteroids.     

Force field and 13C-NMR investigations of substituted cyclopentanes. A concept for the adaption of 13C NMR shifts to varying torsional arrangements in flexible conformers

MM2 Exploration of the conformational space for methylcyclopentane, in contrast to cyclopentanone yields more and flatter minima than known previously. Calculations of cyclopentanes with substituents X = F, Cl, CHMe₂, and CMe₃ with two stable conformations indicate <2° torsional angle changes with the different substituents. Cyclopentanes bearing not more than 2 substituents can accommodate all groups in pseudoequatorial positions without changing the basic envelope and twist chair geometries significantly. A model for ¹³C-shift calculation is proposed in which shift increments for the different torsional arrangements are obtained by linear interpolation between corresponding cyclohexane values. After correction for the nonequivalent carbon shifts in the hydrocarbon itself, again using the linear interpolation, a significant improvement of the shift correlations is observed. For disubstituted cyclopentanes these predict the shifts within ± 1.7 ppm with Me, CHMe₂, CMe₃, Cl, Br and OH as substituents. Configurational assignments are difficult with 1,3-di-substituted cyclopentanes, but straightforward with 1,2-di- and trisubstituted compounds. Thus, due to the presence of smaller torsional angles between, e.g. diequatorial vicinal substituents in the 1,2- cis series as compared to the trans compounds, the latter show deshielding, particularly at C2, by 1–4 ppm. Several epimers are stereo-selectively prepared by suitable ketone reduction and displacement methods.     

2,6-dicyano-1,5-dimethylsemibullvalene as a probe for homoaromatic molecules of the Dewar-Hoffman type

The 2,6-dicyano-1,5-dimethylsemibullvalene (2d) synthesized via the bicyclo[3.3.0]octanedione 7 exists as a classical ground state which is lower in energy by less than 5 kcal/mole than the homoaromatic transition of the Cope rearrangement of 2d.     

Interplay and Competition Between Two Different Types of Redox-Active Ligands in Cobalt Complexes: How to Allocate the Electrons?

The field of molecular transition metal complexes with redox-active ligands is dominated by compounds with one or two units of the same redox-active ligand; complexes in which different redox-active ligands are bound to the same metal are uncommon. This work reports the first molecular coordination compounds in which redox-active bisguanidine or urea azine (biguanidine) ligands as well as oxolene ligands are bound to the same cobalt atom. The combination of two different redox-active ligands leads to mono- as well as unprecedented dinuclear cobalt complexes, being multiple (four or six) center redox systems with intriguing electronic structures, all exhibiting radical ligands. By changing the redox potential of the ligands through derivatisation, the electronic structure of the complexes could be altered in a rational way.     

1,2- and 1,3-diphosphetanes from alkylidenephosphines

Abstract

Alkyl- or arylbis(trimethylsilyl)phosphines as well as tris(trimethylsilyl)phosphine and the corresponding arsines react with acyl chlorides to give [1-(trimethylsiloxy)alkylidene]phosphines 1 and -arsines 2; most of their 2,2-dimethylpropylidene derivatives are thermally stable at room temperature. With the same class of phosphines as starting compounds and carbon disulfide [bis(trimethylsilylsulfano)methylidene]phosphines 3 are formed, whereas [(dialkylamino)methylidene]-4 and [diarylmethylidene]phosphines 5 or the corresponding arsines 6 and 7 can be obtained from acyl amides or ketones.¹     

Modification of polymers by adsorption phenomena

The adsorption of ions and amphiphilic molecules on solid polymers is investigated by direct force measurements using an atomic force microscope (AFM). It is shown that electrolyte ions are changing the surface potentials of the solid polymers as well as their adhesive properties. The experiments show that the interaction with a negatively charged probe is dramatically decreased by the adsorption of anions. The adsorption isotherms are determined by zeta potential measurements (streaming potential of flat plates). In presence of adsorbing anions, the attractive interaction and the adhesion are reduced and can be eliminated completely. So, even solutions of simple electrolyte ions can be applied intentionally in order to modify the interaction of polymer surfaces. A wide variety of technological applications becomes accessible.     

Biologically active metabolites from fungi, 17. 8-alpha-acetoxyverrol,a new member of the trichothecene sesquiterpenes

8-alpha-Acetoxyverrol (4), the first open chain example of the trichothecenes with oxygenation at C-8, was isolated from cultures of Aphanocladium spectabile. The compound doses the biosynthetic gap to the macrocyclic verrucarins.