Estimation scheme for level-dependent uncertainty of analytical result: application for determination of 1-hydroxypyrene in urine

The estimation scheme of uncertainty of determination of 1-hydroxypyrene (1-OHP) in urine was developed analysing the main stages of the analytical procedure: (1) preparation of 1-OHP standards, (2) creation of the calibration curve for the high performance liquid chromatography (HPLC) analysis method with the evaluation of recovery, (3) measuring procedure of aliquot of urine, (4) adjusting the pH of aliquot and hydrolysis with enzyme, (5) solid phase extraction, (6) concentration of the extract, (7) injection of the extract to chromatograph and analysing by the HPLC method, (8) calculation of 1-OHP mass from the calibration curve, (9) calculation of 1-OHP concentration in urine. The evaluation of the uncertainty is based on quantification of individual components. Combined uncertainty was calculated using the law of propagation of uncertainties according to the EURACHEM/CITAC guidelines. Level dependence of the uncertainty arises from the calibration curve. The limits of detection and quantification were found to be equal to 0.03 and 0.1 ng/mL, respectively. The calculated expanded level-dependent uncertainty covers 47–27–25% within the concentration range 0.03–0.1–0.4 ng/mL with the materials and equipment used. These parameters could easily be recalculated according to the proposed scheme if there are some changes in the analysis procedure.     

The polysaccharide extracts from the fungi Coprinus comatus and Coprinellus truncorum do exhibit AChE inhibitory activity

The polysaccharide (PSH) extracts from the edible mushroom species Coprinus comatus and Coprinellus truncorum were screened in liquid for their acetylcholinesterase inhibitory (AChE) activity. Both extracts were found to display inhibition of the aforementioned enzyme reaching similar IC₅₀ values of 0.62 ± 0.07 and 0.61 ± 0.03 mg/mL, respectively. According to the means of FTIR spectroscopy, these PSH extracts mostly contained β-glucans. However, the presence of some proteins and polyphenolics as minor ingredients were also detected. Compared with existing literature data for anti-AChE activity of the sugar samples, the findings within this study may be treated as a profound bioactivity. Consequently, this study puts some light on the possible use of the screened macrofungi in the palliative treatment of Alzheimer’s disease.     

Isothiazoles XI. Diels-alder adducts of 4-isothiazolin-3-one 1-oxides and 1,1-dioxides

4-Isothiazolin-3-one 1-oxides and 1,1-dioxides react with a variety of cyclic and acyclic dienes to afford cycloaddition products.     

Synthesis and properties of 1-(6-methoxy)-2-benzothiazolyl)-2-pyridones

Substituted ]-(6-methoxy-2-benzothiazolyt)-2-pyridones were prepared from 2-amino-6-methoxybenzathiazate through N-(6-methoxy-2-benzothiazotyl) cyanvorearmileaznd-3-aryl-N-(6-methoxy-2-benzothiazolyt)-2-cyano-2-propenamides. The cyclization of the latter with malonodinitrile in the presence of piperidine gave the corresponding pyridones. The structures of the synthesized compounds were confirmed by¹H NMR and mass spectral data.Department of Organic Chemistry, Mass Spectrometry Laboratory, Slovak Technical University, 812 37 Bratislava, Slovakia. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1402–1404, October, 1995. Original article submitted August 24, 1995.     

Zur Kenntnis der thermischen Zersetzung von Ammoniumhexafluoroscandat,-titanat,-vanadat und-chromat

Thermal analysis supported by kinetic calculations was applied exhaustively to these compounds. Under dynamic conditions, tetrafluorometallates(III), which as intermediates, could not be isolated, for the first three compounds. In each case, the final step was the pure metal(III) fluoride. Ammonium hexafluorochromate(III) decomposed directly to the pure chromium(III) fluoride. The decomposition rate of all compounds slowed down towards the end, probably for kinetic reasons. Polymorphic transitions of ammonium hexafluorotitanate(III) were observed at 35 and 100°C. Ammoniumhexafluoroscandate(III) underwent polymorphic transition at 47°C. The decomposition patterns for all these compounds were similar. Conditions for the preparation of pure ammonium tetrafluorometallates(III) of Sc, Ti and V are described.     

The additivity principle in pyrolysis—gas chromatography of brown coal

Pyrolysis—gas chromatography of brown coal exhibits additive properties and it is therefore possible to construct the pyrogram of the original coal from the individual pyrograms of the bitumen, humic acids, lignin and humin fractions. The contents of phenols in the pyrograms are typical for all of the above classes except bitumen and are in agreement with the contents of the individual groups in the original coal. The results suggest that the separation does not bring about significant chemical changes in individual brown coal fractions.     

13C-NMR. Spectroscopy of Naturally Occuring Substances. XLII. Conformational analysis of quebrachamine-like indole alkaloids and related substances

The ¹³C shifts of 16α- and 16β-substituted derivatives of quebrachamine, 14,15-dehydroquebrachamine, cleavamine, 15,20α-dihydrocleavamine and 15,20β-dihydrocleavamine are determined and correlated with possible conformations of these tetracycles. The method of analysis of the C(16) configuration of these compounds, which emanated from this study, is used for the determination of the configuration of the site of coupling of vindoline and cleavamine β-chloroindolenine.     

Amperometric urea biosensor based on urease and electropolymerized toluidine blue dye as a pH-sensitive redox probe

The electropolymerized toluidine blue film deposited on the glassy carbon electrode show amperometrically detectable pH sensitivity. This feature of polytoluidine blue (PTOB) film was used for a construction of an amperometric urea biosensor. We have observed a linear shift of the formal redox potential with increasing pH value between 4 and 8 giving the slope of 81 mV(Delta) pH(-1). Polytoluidine blue film has had a significantly increased stability and higher electrochemical activity compared to the adsorbed monomeric dye. The polytoluidine blue urea biosensor has been operating at a working potential of -200 mV vs. SCE. The sensitivity of the biosensor was 980 nA mM(-1) cm(-2). The biosensor showed linearity in concentration range up to 0.8 mM with the detection limit of 0.02 mM (S/N=3).     

Theoretical investigations of Fe porphyrins. V. Low-lying electronic states of bisammineporphinatoiron(III)

Ab initio CI calculations are reported on the lowest doublet, quartet, and sextet states of [Fe^III(P)(NH₃)₂]⁺. The low-spin ground state is calculated as (d_xy² (d_π)³ with d_xy(d_π)⁴ higher by 0.15 eV. The near-ir bands at ～1 eV observed in low-spin ferriheme proteins are attributed to (π → d_π) transitions. The lowest high-spin state is ⁶A_1g, and the near-ir transitions of the high-spin ferriheme proteins observed at ～1.2 eV are attributed to higher ⁶[tripsextet] excited states [i.e., ring triplet, metal sextet]. The 30-ps “triplet” transient populated with low quantum yield observed in laser-flash studies on Fe^III(TPP)CI [TPP = tetrapbenylporphyrin] may be an ¹[tripsextet] state.     

Matrix elements for spin-adapted configurations

It is shown that the turn-over rule which is used to simplify matrix elements between spin-projected Slater determinants may also be used to simplify formation of matrix elements between any orthonormal set of spin-coupled Slater determinants. The coefficients for the spin-coupling may then be chosen freely to reduce the number of important configurations in the secular equation.