Preparative Droplet Counter-Current Chromatography for the Separation of the New Nor-Seco-Triterpene and Pentacyclic Triterpenoids from Qualea Parviflora

The methanolic extract of the bark of the medicinal plant Qualea parviflora (Vochysiaceae) contains new nor-seco-triterpene and pentacyclic triterpenoids. They were separated in a preparative scale using droplet counter-current chromatography. The optimum solvent used was composed of a mixture of CHCl₃/MeOH/H₂O (43:37:20, v/v) in the descending mode and led to a successful separation of the new compound 28-nor-17, 22-seco-2α, 3β, 19, 22, 23-pentahydroxy-Δ¹²-oleanane, besides the known triterpenoids bellericagenin B, bellericaside B and arjunglucoside I . Identification was performed by ESI-MS, ¹H NMR and ¹³C NMR analyses.     

Effect of cerium, holmium and samarium ions on the thermal and structural properties of the HZSM-12 zeolite

The study of the incorporation of rare earth elements as additives in Y zeolites is a very interesting field of research, mainly by its potential application as additives in catalytic cracking process. In this work was studied the thermal and structural properties of cerium, holmium and samarium supported on HZSM-12 zeolite. The obtained materials were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), nitrogen adsorption, thermogravimetry (TG/DTG), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). TG/DSC/DTA analyses showed that the dehydration temperatures of RE/HZSM-12 zeolites (RE=Ce, Ho, Sm) increase in relation to pure HZSM-12. The acid properties were investigated by pyridine thermo desorption via TG. The results showed two events of mass loss attributed to elimination of pyridine adsorbed on the weak+medium acid sites and on the strong acid sites.     

A two-step conversion of alpha,beta-unsaturated ketones to their alpha-carbalkoxy or alpha-carbamoyl derivatives

Several enones are converted into their alpha-iodo derivatives in excellent yields and carbonylated with palladium catalysis in the presence of alcohol or amines to the alpha-carbonyl enones in satisfactory yields.     

Lanthanide nitrate complexes with 2-azacyclononanone

Thermal behavior of rare earth nitrate complexes with 2-azacyclononanone (AZA) with Ln(NO₃)₃·3(AZA) composition (where Ln=Gd, Er and Ho) was analyzed in kinetic point of view. Kinetic parameters were calculated from thermogravimetric data. All obtained results were similar. The first decomposition step was representative to the loss of ligand and the residue was essentially Ln₂O₃. Furthermore, a reaction path was proposed for the thermal decomposition of the Ln(NO₃)₃·3(AZA).     

Coupling of a Rydberg electron capture ion source with a quadrupole mass filter

The coupling of a Rydberg electron capture ion source with a Nermag R10-10H quadrupole mass filter is described. Details are given of the addition to this instrument of a creation cell for atoms excited in Rydberg states. Within the Nermag ion source, such atoms allow attachment of electrons of well-defined thermal energy. SF(6) was used for optimization of the main experimental parameters (gas pressures and voltages applied to the electrodes). The procedure by which Rydberg electron attachment was confirmed is described. A polychlorobiphenyl compound was used to illustrate the performance of this ionization technique. Ion formation was observed in the absence of fragmentation.     

Effect of radial distribution functions and poisson reparatition of reactants on the analysis of reactions involving long distance energy transfer

Starting from a uniform distribution and knowing the space dependent rate constant, it is possible to express the fluorescence quenching effect. In the case of long distance energy transfer (Forster), we show that the introduction of radial distribution functions and of non-uniform repartition of quenchers has only small effects on the kinetics of such reactions.

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. (Forster) , .

     

Thermal and mechanical properties of PE/organoclay nanocomposites

Polyethylene/montmorillonite clay nanocomposites were obtained via direct melt intercalation. The clay was organically modified with four different types of quaternary ammonium salts. The objective of this work is to study the use of montmorillonite clay in the production of nanocomposites by means on rheological, mechanical and crystallization properties of nanocomposites and to compare to the properties of the matrix and PE/unmodified clay nanocomposites. In general, the tensile test showed that the yield strength and modulus of the nanocomposites are close to the pure PE. Apparently, the mixture with Dodigen salt seems to be more stable than the pure PE and PE/unmodified clay.     

Inhibition of folylpolyglutamate synthetase by substrate analogues with an ornithine side chain

N^α-[4-[[(4-Aminopteridin-6-yl)methyl]amino]benzoyl]-L-ornithine (dAPA-Orn) was synthesized, and its ability to inhibit folylpolyglutamate synthetase from mouse liver was compared with that of the corresponding 2,4-diamino analogue APA-Orn. Also compared were the inhibitory activities of the deaza analogues 5-deazaAPA-Orn, 8-deazaAPA-Orn, and 5,8-dideazaAPA-Orn, as well as those of N^α-pteroyl-L-ornithine (PteOrn) and its deaza analogues 5-deazaPteOrn and 5,8-dideazaPteOrn. The inhibition constant K_i of dAPA-Orn was 7-fold greater than that of APA-Orn, indicating that the 2-amino group plays a role in binding to the active site. The binding affinity of the 2,4-diamino compounds increased in the order 5-deazaAPA < APA-Orn <5,8-dideazaAPA-Orn < 8-deazaAPA-Orn, and that of the 2-amino-4(3H)-oxo compounds increased in the order 5-deazaPteOrn < PteOrn < 5,8-dideazaPteOrn. The most potent inhibitor of both groups was 8-deazaAPA-Orn, with a K_i of 0.018 μM, coresponding to an 8-fold and 15-fold increase in affinity relative to APA-Orn and 5-deazaAPA-Orn, respectively. The results suggest (a) that the binding of Orn-containing folylpolyglutamate synthetase inhibitors is affected to a greater degree by replacement of N⁸ by a carbon atom than it is by the corresponding change at N⁵, (b) that the effect of carbon for nitrogen replacement is greater in the 2,4-diamino derivatives than in the 2-amino-4(3H)-oxo compounds, and (c) that the 2,4-diamines are the better inhibitors. Comparison of the K_i values of the Orn-containing inhibitors with the K_m values of the corresponding glutamate-containing substrates revealed that K_m/K_i ratio can vary as much as 100-fold depending on the nature of the heterocyclic moiety, suggesting that caution should be exercised in using K_m values of known substrates to predict K_i values of putative inhibitors.     

Synthesis of the lipophilic antifolate piritrexim via a palladium(0)-catalyzed cross-coupling reaction

[reaction: see text] A regiospecific and convergent route the lipophilic antifolate piritrexim (PTX) is described in which a key step is a Pd(0)-catalyzed cross-coupling reaction between 2-amino-3-cyano-4-methyl-5-bromopyridine and 2,5-dimethoxybenzylzinc chloride to form 2-amino-4-methyl-5-(2,5-dimethoxybenzyl)nicotinonitrile. To complete the synthesis, the amino group is replaced by a more reactive bromine atom via nonaqueous diazotization with tert-butyl nitrite, and the resultant bromo nitrile is cyclized with guanidine.     

Computation of LCAO wave functions for ground states of polymers and solids

The LCAO form of the Hartree–Fock method is discussed in its application to crystals. General formulae are given for obtaining Fourier coefficient of electronic density (in direct space) as well as of the band structure (in momentum space). Finally, it is shown that in its LCAO form, Slater–Hartree–Fock equations are very simple and that this method is of interest for numerical applications. Special integrals occurring in this formalism are evaluated for a Gaussian basis in the last part of this paper.