NiCl2-catalyzed hydrophosphinylation

[reaction: see text] A new nickel-based catalytic system has been developed for phosphorus-carbon bond formation. The addition of alkyl phosphinates to alkynes is catalyzed by nickel chloride in the absence of added ligand. The reaction generally proceeds in high yields, even with internal alkynes, which were poor substrates in our previously reported palladium-catalyzed hydrophosphinylation of alkyl phosphinates. The method is useful for the preparation of H-phosphinate esters and their derivatives. The one-pot synthesis of various important organophosphorus compounds is also demonstrated. The reaction can be conducted with microwave heating.     

Total synthesis of emericellamides A and B

A concise total synthesis of emericellamides A and B, two cyclic depsipeptides exhibiting antibacterial and cytotoxic activities, is reported. A Paterson anti-aldol reaction and a hydroxy directed 1,3-anti reduction were applied for construction of the polypropionate unit with the required stereochemistry in emericellamides A and B. An FDPP mediated macrolactamization was used to construct the macrocycle of emericellamides A and B.     

Cladonia verticillaris (lichen) can exhibit defense mechanisms against Rn-222 under controlled conditions

Journal of Radioanalytical and Nuclear Chemistry - This study aimed to evaluate the effects of the Rn-222 progeny on the lichen Cladonia verticillaris under controlled conditions. The results...     

Characterization of the Simultaneous Decay Kinetics of Metarhodopsin States II and III in Rhodopsin by Solution‐State NMR Spectroscopy

The mammalian visual dim‐light photoreceptor rhodopsin is considered a prototype G protein‐coupled receptor. Here, we characterize the kinetics of its light‐activation process. Milligram quantities of α,ε‐¹⁵N‐labeled tryptophan rhodopsin were produced in stably transfected HEK293 cells. Assignment of the chemical shifts of the indole signals was achieved by generating the single‐point‐tryptophan to phenylalanine mutants, and the kinetics of each of the five tryptophan residues were recorded. We find kinetic partitioning in rhodopsin decay, including three half‐lives, that reveal two parallel processes subsequent to rhodopsin activation that are related to the photocycle. The meta II and meta III states emerge in parallel with a relative ratio of about 3:1. Transient formation of the meta III state was confirmed by flash photolysis experiments. From analysis of the site‐resolved kinetic data we propose the involvement of the E₂‐loop in the formation of the meta III state.     

Absence of Differential Correlations Between the Wave Equations for Upper-Lower One-Index Twistor Fields Borne by the Infeld-van derWaerden Spinor Formalisms for General Relativity

It is pointed out that the wave equations for any upper-lower one-index twistor fields which take place in the frameworks of the Infeldvan der Waerden γε-formalisms must be formally the same. The only reason for the occurrence of this result seems to be directly related to the fact that the spinor translation of the traditional conformal Killing equation yields twistor equations of the same form. It thus appears that the conventional torsionless devices for keeping track in the γ-formalism of valences of spinor differential configurations turn out not to be useful for sorting out the typical patterns of the equations at issue.     

Copolymers of Bromine-Containing Monomers. 5. Terpolymerization of Acryionitrile,Styrene, and Pentabromophenyl Acrylate

The terpolymerization of acryionitrile, styrene, and pentabromophenyl acrylate in dimethylformamide solution was investigated. Experimental terpolymerization data agreed well with calculations using the Alfrey-Goldfinger equation. The relationship between monomer feed and terpolymer compositions are presented on triangular coordinate graphs, and the lines of unique and the lines of binary azeotropic composition were identified. No point of true ternary azeotropic composition was found but a “pseudoazeotropic” region was identified. The experimental results of the terpolymerization agreed well with the theoretical curves over a wide range of monomer composition up to high conversions. The influence of pentabromophenyl acrylate units on the thermal and flammability characteristics of the terpolymers are described.     

Distribution and environmental impact of radionuclides in marine sediments along the Venezuelan coast

The activity concentrations of ¹³⁷Cs, ⁴⁰K, ²²⁶Ra and ²³²Th in Bq/kg from 42 marine sediment samples collected at nine sampling sites were determined in order to establish a radiological baseline along the Venezuelan coast. The radioactivity levels were determined by means of a gamma-ray spectroscopy system using a hyper-pure germanium detector in a low-background configuration. Particle size distribution and total organic matter content were also determined. Activity concentrations of ¹³⁷Cs were lower than the detection limit of the analytical technique (0.9 Bq/kg) in all studied sites. The results suggest that the variation of grain-size distribution is one of the most important factors influencing the spatial variations of ⁴⁰K, ²²⁶Ra and ²³²Th in sediments along the Venezuelan coasts. In all sampling sites, average concentrations of ⁴⁰K, ²²⁶Ra and ²³²Th were lower than the world average values. Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in coastal marine sediments along the Venezuelan coast could be considered to be low when compared with global average values, indicating that they are not apparently above of the range that might be considered normal or background. These results suggest that the studied sites do not pose any significant radiological threat to the population. The results attained in this study should be of considerable value as baseline data and background reference levels for Venezuelan coastlines.     

Synthesis,characterization, crystal structure determination,catalytic activity and thermal study of a new oxidovanadium(IV) Schiff base complex: production of V2O5 nano-particles

A new oxidovanadium(IV) Schiff base complex, VOL₂ (1), containing furfuryl pendant group was synthesized by the reaction of the related bidentate O, N-type Schiff base ligand and VO(acac)₂ in the ratio of 2:1 in methanol in the reflux conditions. The Schiff base ligand and its vanadyl complex were characterized by ¹H-NMR and FT-IR spectra and elemental analysis. The crystal structure of 1 was also determined the single-crystal X-ray analysis. It showed that the metal center located in a distorted tetragonal pyramidal (N₂O₃) geometry in which the two bidentate Schiff base ligands were coordinated to the vanadium(IV) ion in four equatorial positions, and one oxygen atom in its axial position. The catalytic activity of the vanadyl Schiff base complex was elucidated in the epoxidation of cyclooctene as a model substrate. Different reaction parameters were investigated in this reaction and the results showed that it was an effective and selective catalyst in these optimal conditions. Thermogravimetric analysis of 1 showed that it was decomposed in two stages by losing two methoxy groups and other organic residuals, respectively, in the temperature range of 253–532 °C. In addition, the vanadyl Schiff base complex (1) was thermally decomposed in air at 660 °C and the XRD pattern of the obtained solid showed the formation of the V₂O₅ nano-particles with the average size of 52 nm.     

The Use of Chiral Auxiliaries Prepared from (-)-β-Pinene in Stereoselective Reduction of β-Ketobutyrates

Chiral auxiliaries previously prepared from (-)-β---pinene (3), alcohols 5a-e and 6, were transformed into β---ketobutyrates 7a-e and 8 respectively. These compounds were stereoselectively reduced by NaBH₄ in the presence of additives (MnCl₂ or CaCl₂), leading to the corresponding β-hydroxy butyrates 10a-e and 11 in good chemical yield and poor to moderate stereoselectivities (de 0%-60%). The configuration at the newly generated stereogenic center in 10a was determined to be S through its transformation into S-(+)-butanediol.