The influence of Lewis acid catalyst on the kinetic and molecular mechanism of nitrous acid elimination from 5-nitro-3-phenyl-4,5-dihydroisoxazole: DFT computational study

Chemistry of Heterocyclic Compounds - The molecular mechanism of nitrous acid elimination from 5-nitro-3-phenyl-4,5-dihydroisoxazole systems has been explored using DFT computational study. It was...     

Being uncertain in thin layer chromatography—Some thoughts about latent details in the retention estimation

This paper deals with some important (but often neglected) details about the uncertainty of retention measurement in thin layer chromatography, the propagation of uncertainty during computing simple and more complex values from the retention data, ending in influence of the retention uncertainty onto the regression estimates during extrapolation and lipophilicity estimation. Theoretical considerations are tested on data from previous study. It can be concluded that when TLC spots are broad and the retention uncertainty exceeds about 0.02 of R_F value, the uncertainty should be taken into the account in further computations.     

Tetrahydrophthalic esters of prednisolone

The two biologically active isomers of prednisolone tetrahydrophthalate have been studied by X-ray diffraction methods. The compounds crystallize in the orthorhombic system in the space groupP2₁2₁2₁, with similar lattice parameters. The isomers differ both in configuration [(1′S),(6′R) isomerA and (1′R),(6′S) isomerB] and conformation of the thetetrahydrophthalic part of the molecules. Cell parameters of isomerA:a=9.595(2),b=14.465(2),c=18.988(3) Å andB:a=9.114(2),b=14.283(6),c=20.398(5) Å. The O(3) carbonyl oxygen atom interactsvia hydrogen bonds with three neighboring molecules accepting hydrogen bonds from two hydroxyl groups and one carboxylic group. Additional short intermolecular C?H…O type contacts occur in the structure of theB isomer, which has a somewhat larger unit cell and significantly higher melting point.     

pH gradient reversed-phase liquid chromatography as a fractionation tool for the separation of peptides

Recent reports from our laboratory presented a comprehensive theory and demonstrated feasibility of reversed-phase liquid chromatography (RP-LC) employing the programmed gradient of pH of the mobile phase. The aim of that work was to explore the usefulness of the pH gradient-based approach in fractionation of peptides. The experiments were performed on a series of peptides separated at various LC conditions. Retention parameters of peptides in the pH gradient and in the simultaneous pH/organic modifier gradient RP-LC were compared. The best results were obtained with eluents comprising low but constant concentrations of organic modifier while gradient of pH in the mobile phase was developed several times during each chromatographic run. The elaborated LC conditions allowed controlling the elution of peptides not only according to their hydrophobic properties, but also taking into account their electronic properties, represented by isoelectric point (pI) values. The combination of isocratic (regarding organic modifier) LC mode with recurring eluent pH gradient is proposed as an effective fractionation method of peptide mixtures. Moreover, information on hydrophobicity and pI of the peptides, obtained by that approach, might be an additional peptides database matching constraint. Hence, a new tool for analytical and bioinformatics studies of peptides fractionation is proposed.     

Platinum(IV) complexes with purine analogs. Studies of molecular structure and antiproliferative activity in vitro

A series of tetrachloride platinum(IV) compounds of the general formulae PtCl₄L₂, where L = 1,2,4-triazolo[1,5-a]pyrimidine (tp) (1), 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) (2), 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) (3) and 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one (HmtpO) (4) have been prepared and characterized by thermal analysis, ¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt NMR and IR spectroscopy. Spectral data suggest that the triazolopyrimidines act as a monodentate ligand via the nitrogen atom N(3). The preliminary assessments of antitumor properties of the four complexes were evaluated as in vitro antiproliferative activity against three cell lines: HL-60 human acute promyelocytic leukemia, SW707 rectal adenocarcinoma and HCV29T bladder cancer. PtCl₄(dbtp)₂ exhibits high cytotoxic activity against all human cell lines, whereas the other complexes are only moderately active.     

Automatic code generation for quantum chemistry applications

A unified, computer algebra system‐based scheme of code‐generation for computational quantum‐chemistry programs is presented. Generation of electron‐repulsion integrals and their derivatives as well as exchange‐correlation potential and its derivatives is discussed. Application to general‐purpose computing on graphics processing units is considered.     

Gold Surface Functionalization with S‐containing Organic Compounds and Gold Nanoparticles for Ethylene Glycol Electrooxidation

In this work a gold electrode modified with self‐assembled layers (SAMs) composed with organic S‐containing compound and gold nanoparticles was prepared. The electrode with SAMs endowed with gold nanoparticles gave the high catalytic effect for ethylene glycol (EG) electrooxidation in solution at pH 7. For this novel sensor a linear relationship between the current response of EG at the potential of peak maximum (j_p) and the concentration of this compound in solution (c_EG) was found over the range 0.1 µM to 0.7 M with the detection sensitivity j_p/c_EG equal to about 5 A cm^?2 mol^?1 dm³ (at v=0.1 V s^?1) and the detection limit of 0.046 µM.     

Comparative validation of amisulpride determination in pharmaceuticals by several chromatographic, electrophoretic and spectrophotometric methods

Depleted uranium (DU) is a by-product of the uranium enrichment process for nuclear fuel. According to the Commission Decision 2002/657/EC, a confirmatory method for the quantification of DU in freeze-dried fish was developed by isotope ratio dynamic reaction cell inductively coupled plasma-mass spectrometry (IR-DRC-ICP-MS). A preliminary study was performed to determine the following parameters: instrumental detection limit (IDL), isotopic ratio measurement limit (IRML), percentage of DU (P(DU)) in presence of natural uranium (NU) and limit of quantification (LoQ(DU)). The analyses were carried out by means of IR-DRC-ICP-MS. Ammonia was the reaction gas used for the dynamic reaction cell. In addition, a sector field inductively coupled plasma mass spectrometer (SF-ICP-MS) was employed to calculate the within-laboratory reproducibility. For the confirmatory method the following parameters were determined: (a) trueness; (b) precision; (c) critical concentrations alpha and beta (CC(alpha), CC(beta)); (d) specificity; (e) stability. Trueness was assessed by using the recovery tests. The recovery and within-laboratory reproducibility were determined by fortifying the blank digested solution of dogfish tissue: six aliquots were fortified at 1, 1.5 and 2 times the LOQ(DU) with 25.0, 37.5 and 50.0 ng L(-1) or 4.16, 6.24, 8.32 microg kg(-1) with a recovery of -8.2, +9.5 and +9.6%, respectively and a within-laboratory reproducibility (three analytical run) of 15.5, 8.0 and 11.0%, respectively. The results for the decision limit and the detection capability were: CC(alpha) = 11.69 ng L(-1) and CC(beta) = 19.8 ng L(-1). The digested solutions resulted to be stable during testing time (60 days) and the method can be considered highly specific as well.