The Adsorption of Polyvinylpyrrolidone on Kaolinite Saturated with Sodium Chloride

The adsorption of two different molecular weights of polyvinylpyrrolidone (PVP) (M(w)=44,000 and M(w)=360,000 g mol(-1)) from water on kaolinite saturated with sodium chloride has been studied. The adsorption of PVP increases slowly as temperature increases. The adsorption of PVP on the kaolinite was studied by considering Fourier transform infrared (FTIR) spectra, X-ray diffraction patterns, and dielectric constants. During the adsorption process, PVP interacts with saturating sodium cations and possibly forces some of them onto the edges of the kaolinite; thus, the dielectric constant of saturated kaolinite is reduced after PVP adsorption. Copyright 2001 Academic Press.     

Alkylation of β-diketones through their co(II), co(III) and zn(II) complexes. 1-Bromoadamantane as alkylating agent.

α-(1-adamantyl)-β-diketones are now accessible by the alkylation of Co(II) complexes of β-diketones with 1-bromoadamantane. The intermediacy of adamantyl cation is proposed. Co(II), Co(III) and Zn(II) complexes of pentane-2,4-dione react with alkyl halides precursors of stabilized carbenium ions, to give 3-alkylpentane-2,4-diones.     

Identification of barbiturates from extracts of urine,stomach fluid,liver and kidney by high-performance liquid chromatography and field desorption mass spectrometry1,2

The characteristic behaviour of a series of important barbiturates in field desorption mass spectrometry (f.d.m.s.) is described. Detection limits are reported for three standard barbiturates by f.d.m.s. and high-performance liquid chromatography (h.p.l.c.). The off-line combination of h.p.l.c. and f.d.m.s. is used in forensic investigations to identify these drugs unequivocally in body fluids such as urine and stomach fluids and in extracts from human liver and kidney tissues. Eighteen barbiturates were tested. The use of f.d.m.s. as an off-line h.p.l.c. detector provides detection limits (S/N =3:1) ranging from 1 ng g^-1 to 10 ng g^-1, depending on the compound and on the preliminary clean-up used.     

Evaluation of measurement uncertainty for analytical procedures using a linear calibration function

In the EURACHEM/CITAC draft ”Quantifying uncertainty in analytical measurement” estimations of measurement uncertainty in analytical results for linear calibration are given. In this work these estimations are compared, i.e. the uncertainty deduced from repeated observations of the sample vs. the uncertainty deduced from the standard residual deviation of the regression. As a result of this study it is shown that an uncertainty estimation based on repeated observations can give more realistic values if the condition of variance homogeneity is not correctly fulfilled in the calibration range. The complete calculation of measurement uncertainty including assessment of trueness is represented by an example concerning the determination of zinc in sediment samples using ICP-atomic emission spectrometry. Received: 9 February 2002 Accepted: 17 April 2002     

Adsorption of N-Nitrosodiethylamine and N-Nitrosodimethylamine on Activated Carbon: A Pre-Concentration Procedure for Gas Chromatographic Analysis

In this study, a rapid pre-concentration procedure, which employs powdered activated carbon as a clean-up and pre-concentration material, is described for the gas chromatographic analysis of N-nitrosodiethylamine (NDEA) and N-nitrosodimethylamine (NDMA) in aqueous solutions. It was found that powdered activated carbon is suitable for the adsorption of volatile N-nitrosamine compounds from aqueous solutions. Adsorption efficiency with spiked beer samples (alcohol content 5% v/v) was found to be 80.5% (NDMA) and 89.4% (NDEA) and recovery of extraction from activated carbon was calculated as 82.1% (NDMA) and 89.7% (NDEA), respectively. The effect of 100µgmL^–1 of tannic acid on the adsorption was also studied, and no significant effect on the adsorption and extraction of volatile N-nitrosamine compounds was found.     

Heterocycles by PtCl2-catalyzed intramolecular carboalkoxylation or carboamination of alkynes

PtCl2 constitutes a convenient catalyst for intramolecular hydroalkoxylation, carboalkoxylation, hydroamination, and carboamination reactions of alkynes, effecting the formation of substituted benzo[b]furan, indole-, and isochromene-1-one derivatives, respectively. This procedure allows for the transfer of (substituted) allyl, methoxymethyl (MOM), benzyloxymethyl (BOM), and (trimethylsilyl)ethoxymethyl (SEM) groups from oxygen to carbon and is compatible with functional groups that are susceptible to oxidative insertion of low valent metal species previously used for similar purposes. Although some of the reactions can even be carried out in air, the rates are significantly increased when conducted under an atmosphere of CO. A mechanistic rationale is proposed, implying activation of the alkyne by the carbophilic Pt(2+) template as the primary step of the catalytic cycle.     

Synthese von 2-methylalanin-peptiden,die pH-Abhängiggkeit ihrer 13C-NMR-spektren und eine neue methode zur auswertung über CS-diagramme

The uncommon amino-acid 2-methylalanine (α-aminoisobutyric acid, Aib) was investigated by ¹³C-NMR. The chemical shifts of amino- or carboxy-protected derivatives of Aib and of protected oligopeptides are discussed with respect to neighbouring groups and amino acids. The pH-dependence of the ¹³C-NMR spectra of Aib, Aib-Ala, Ala-Aib, Aib-Ala-Aib and Aib-Ala-Aib-Ala-Aib was studied. Using these examples, a new and advantageous method is demonstrated for the first time for the evalutions of NMR titration curves, which uses so-called chemical shift diagrams (CS diagrams).     

Syntheses of dictyopterene B (hormosirene) and its enantiomer via asymmetric ScN′ reactions

Stereocontrolled syntheses of dictyopterene B (hormosirene) (1) and its enantiomer (ent-1) are reported. Key steps are highly stereoselective S_cN′ reactions of esters of alcohols 2 and 5 derived from (+)-camphor.     

Treatment of anions in SINDO1

The SINDO1 method is modified to include the calculation of molecular anions. Two versions of modifications are presented which are based on charge dependent orbital exponents. Calculated heats of formation and electron affinities are much improved compared to the standard version with fixed orbital exponents.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday