Allylic and benzylic oxidation using cobalt(II) alkyl phosphonate modified silica

The allylic and benzylic oxidation of a range of substrates proceeds in good yield using catalytic quantities of cobalt(II) alkyl phosphonate modified silica and tert-butyl hydroperoxide.     

Use of Two-Dimensional TLC to Identify Phenolic Acids in the Foliage and Fruit of Peucedanum tauricum Bieb.

JPC – Journal of Planar Chromatography – Modern TLC - Two-dimensional planar chromatography (2D TLC) on cellulose layers, solid phase extraction (SPE), and reversed-phase...     

Charm quark energy loss at RHIC

Heavy quark energy loss in a hot QCD plasma is computed taking into account the competing effects due to suppression of zeroth order gluon radiation below the plasma frequency and the enhancement of gluon radiation due to first order medium induced bremsstrahlung. The results suggest a surprising degree of cancellation between the two medium effects for charm quarks and provide a possible explanation for the null effect observed by PHENIX in the prompt electron spectrum in Au+Au at √s = 130 AGeV. In this paper only the main results for heavy quark energy loss will be presented. For more detailed version see [1] and references therein.     

Reductive carbonylation of nitrobenzene over Pd/Fe/I2/Py and Pd/C/Fe/I2/Py catalytic systems

A simple catalytic system containing metallic palladium, iron and iodine has been shown to be very active in the carbonylation of nitrobenzene to carbamate. The influence of the components of the catalytic system studied on its selectivity and activity has been established. It has been found that the catalytic activity of palladium supported on carbon (using both lignite coal and bituminous coal) was not lower than the activity of metallic palladium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Rearrangement of 2-methyl-2,3-epoxypentane: a kinetic study

The kinetics of the rearrangement of 2-methyl-2,3-epoxypentane over ZnCl₂/pumice stone is reported. 2-Methyl-3-pentanone and 2,2-dimethylbutanal are formed in parallel reactions. The reaction scheme and kinetic equations best fitting the experimental data are given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cyclization versus oligomerization of SP- and RP-5′-OH-N-benzoyl-2′-deoxycytidine-3′-O-(2-thio-4,4-pentamethylene-1,3,2-oxathiaphospholane)s

The S_P-isomer of 5′-OH-N⁴-benzoyl-2′-deoxycytidine-3′-O-(2-thio-4,4-pentamethylene-1,3,2-oxathiaphospholane) undergoes DBU-promoted intramolecular cyclization providing as a sole product S_P-deoxycytidine cyclic 3′,5′-O,O-phosphorothioate. Unexpectedly, the R_P-counterpart yields a mixture of products consisting of R_P-deoxycytidine cyclic 3′,5′-O,O-phosphorothioate and macrocyclic oligo(deoxycytidine phosphorothioate)s. The results of molecular modeling indicate that the dychotomy observed for the R_P substrate may result from remarkably higher energy of the corresponding transition states, caused by the presence of bulky ‘spiro’ pentamethylene substituent at the position C4 in the oxathiaphospholane ring.     

Potentiometric studies on the complex formation of lanthanides with proline and hydroxyproline

The formation of the lanthanide (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu) complexes with proline and hydroxyproline has been investigated by potentiometric methods as well as by a turbidimetric one which has provided some additional conclusions. It has been found that 11 and a slight amount of 21 complexes are formed. The deviation from the typical course of the formation function is discussed. It is suggested that the perturbations of complex formation in the systems are caused by hydrolysis. The stability constants of the complexes are reported.

---

Potentiometrische Untersuchungen an Lanthanid-Komplexen von Prolin und Hydroxyprolin

Zusammenfassung Die Bildung von Lanthanid-Komplexen (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu) mit Prolin und Hydroxyprolin wurde potentiometrisch und mit Hilfe von Trübungsmessungen untersucht. Es wurde festgestellt, daß sich Komplexe der Zusammensetzung 11 und in kleiner Menge auch 21 bilden. Die Abweichung von typischem Verlauf der Bildungskurven wurde untersucht. Es wurde dabei festgestellt, daß für die Störungen in der Komplexbildung die Hydrolyse verantwortlich ist. Die Stabilitätskonstanten wurden bestimmt.

     

Improper hydrogen C-H...O bonds cause self-association of alpha, beta-enaminoketones containing fluorosubstituted alkyl groups.

Concentration- and temperature-dependent IR, NMR and dipole-moment studies on 4-N,N-dimethylamino-1,1,1-trifluoro-3-buten-2-one and two of its higher homologues showed that these compounds undergo reversible dimerization in nonpolar solvents. Antiparallel "closed" dimers are formed with a network of improper intermolecular C-H...O hydrogen bonds. Quantitative analysis of the 1H NMR data yielded delta H0 = -17.6 kJ mol-1 and delta S0 = -46.9 J deg-1 mol-1. The interactions observed are the strongest among those involving a C-H group reported so far. The complex described here is the first example of a cyclic complex stabilized by two improper C-H...O hydrogen bonds. The conclusions drawn from the solution and solid-state data were confirmed by ab initio calculations.     

Synthesis of Purine and Pyrimidine 3'-Amino-3'-deoxy- and 3'-Amino-2',3'-dideoxyxylonucleosides

A general procedure to obtain the 3'-aminoxylonucleosides 13a,b and 17a,b is presented. The synthetic scheme is based on the 5' directed intramolecular nucleophilic substitution at the 3'-activated position of the nucleoside. The approach of the incoming group to this position takes place regio- and stereoselectively from the most hindered face of the nucleoside. The methodology presented is applicable to ribonucleosides and 2'-deoxyribonucleosides, regardless of their nitrogenated base.