Computer simulation of the uncertainty of analytical results

Uncertainty is an important quality parameter of any analytical result. Estimating the uncertainty of analytical procedures can be rather difficult in many instances. Computer simulation based on multiple repetition of calculation of the resulting quantity while varying slightly the input parameters is an alternative option. The input parameters for the various computation runs are composed of two terms: the constant mean value and the error, obtained as the product of the standard uncertainty of the parameter in question and a random number with the normal distribution N(0.1). This approach can also serve to optimize measuring procedures, as demonstrated on an example of the determination of lead in biological materials by isotope dilution mass spectrometry. The accuracy of the optimized method was tested by analysis of some CRMs, the robustness of the method was examined, and the detection limit (10 ng/g Pb) and repeatability (4 ng/g Pb) were determined. Received: 30 September 1998 / Revised: 3 December 1998 / Accepted: 8 December 1998     

Comparison of mobility shift affinity capillary electrophoresis and capillary electrophoresis frontal analysis for binding constant determination between human serum albumin and small drugs

In this study, two capillary electrophoresis–based ligand binding assays, namely, mobility shift affinity capillary electrophoresis (ms-ACE) and capillary electrophoresis-frontal analysis (CE-FA), were applied to determine binding parameters of human serum albumin toward small drugs under similar experimental conditions. The substances S-amlodipine (S-AML), lidocaine (LDC), l -tryptophan (l -TRP), carbamazepine (CBZ), ibuprofen (IBU), and R-verapamil (R-VPM) were used as the main binding partners. The scope of this comparative study was to estimate and compare both the assays in terms of their primary measure's precision and the reproducibility of the derived binding parameters. The effective mobility could be measured with pooled CV values between 0.55% and 7.6%. The precision of the r values was found in the range between 1.5% and 10%. Both assays were not universally applicable. The CE-FA assay could successfully be applied to measure the drugs IBU, CBZ, and LDC, and the interaction toward CBZ, S-AML, l -TRP, and R-VPM could be determined using ms-ACE. The average variabilities of the estimated binding constants were 64% and 67% for CE-FA and ms-ACE, respectively.     

Extending the application potential of capillary electrophoresis/frontal analysis for drug-plasma protein studies by combining it with mass spectrometry detection

CE/frontal analysis (CE/FA) is probably one of the most frequently used modes of CE for studying affinity interactions. It is typically performed with classic UV-Vis detection that suffers from low concentration sensitivity. To overcome this limitation, the applicability of CE/FA in combination with ESI-MS detection for the investigation of drug–HSA interactions was demonstrated. The developed new method combines the advantages of CE/FA, such as low sample consumption and no labeling or immobilization of interacting partners, with the benefits of MS detection, such as higher selectivity and sensitivity; moreover, it can be used for molecules lacking a fluorophore or chromophore. The binding parameters of tolbutamide (TL) and glimepiride (GLP), first- and second-generation antidiabetics that differ strongly in their solubility in aqueous solutions, were investigated by this CE/FA-MS method. This method, in contrast to the CE/FA method with the most commonly used UV-Vis detection, is more sensitive; an almost three times lower LOD was reached. The binding parameters of TL and GLP were investigated by this CE/FA-MS method and compared with the literature data. The binding constant value of TL obtained by UV-Vis detection was lower than the value obtained by the method hyphenated with MS detection, which is probably given by the influence of the ESI parameters on the stability of drug–HSA complex. In addition, the ratio of TL and HSA concentrations was divergent in both of the experimental approaches. Finally, it can be concluded that both detection methods have their strengths and weaknesses.     

Diffusion Transport in Reconstructed Semi-Crystalline Structure of Polyolefins

Summary: Diffusion of penetrants (e.g., monomers) in polyolefins is important not only in their manufacturing and down-stream processing, but also in packaging and separation applications. We propose a general methodology linking the semi-crystalline structure of polyolefins to their application properties. This methodology comprises of AFM imaging of semi-crystalline structure, reconstruction of 3D replica of semi-crystalline polymer and calculation of application properties (e.g., diffusivity) depending on 3D morphology. Our algorithm is capable to achieve realistic crystallinities of reconstructed samples up to 70% and to reconstruct spherulites with preferential orientation of lamellae. We demonstrate and discuss difficulties experienced during AFM imaging of HDPE morphology, particularly the dependence of resulting AFM image representing the distribution of crystalline domains on the sample preparation including etching.     

Enhanced acidity, photophysical properties and liposome binding of perfluoroalkylated phthalocyanines lacking C-H bonds

The acid-base, spectroscopic, photophysical and liposome-binding properties of the recently synthesized free base, 29H,31H,1,4,8,11,15,18,22,25-octafluoro-2,3,9,10,16,17,23, 24-octakisperfluoro(isopropyl) phthalocyanine, F64PcH2, are reported. The perfluoroalkylation of the phthalocyanine core renders the hydrogen atoms acidic, with a pK(a) = 6. The F64Pc(-2) dianion is detected already at pH 3, by singular-value decomposition analysis of electronic spectra. F64Pc(-2) generates 1O2 with quantum yields phi(delta) = 0.252 (in MeOH) and 0.019 in liposomes. Metallation of the Pc macrocycle to yield F64PcZn increases phi(delta) to 0.606 and 0.126 in MeOH and liposomes, respectively. Surprisingly, F64Pc(-2) (but not F64PcH2 or F64PcZn) binds strongly to liposomes, with a binding constant K(b) = 25 (mg/mL)(-1). The fully protonated F64PcH2, but not the zwitterionic F64Pc(-2), might favor hydrogen bonding, thus reducing its lipophilicity. Similarly, the Lewis acidity of Zn in F64PcZn, and thus its ability to bind water within a hydrophobic perfluoroalkyl pocket, is significantly enhanced by the fluorinated substituents.     

Investigation of vanadocene(IV) alpha-amino acid complexes: synthesis, structure, and behavior in physiological solutions, human plasma, and blood

This work is focused on investigating the interaction of antitumor active metallocene vanadocene dichloride (Cp2VCl2) and amino acids in aqueous solution at physiological pH. Sixteen vanadocene amino acid complexes [Cp2V(aa)][X] (aa = gly, ala, val, leu, ile, phe, his, and trp; X = Cl, PF6) were prepared and characterized on the basis of spectral measurements (EPR, MS, IR, Raman). Amino acids are coordinated to the vanadocene fragment through the oxygen atom of the carboxylic group and the nitrogen of the amino group, resulting in a five-membered chelate ring. Complexes [Cp2V(val)][PF6] and [Cp2V(ile)][PF6] have been characterized by X-ray structure analyses. It was evidenced that all prepared complexes are stable in both aqueous solutions with physiological pH and in therapeutic NaCl solutions. EPR spectra of vanadocene amino acid complexes in Krebs-Ringer solution in human blood plasma and in whole blood showed that these complexes react with the hydrogen carbonate anion present forming complex Cp2V(O2CO).     

Preparation of phosphinoferrocene carboxamides from isocyanates. Synthesis and structural characterisation of palladium(II) and platinum(II) complexes with 1′-(diphenylphosphino)-1-(N-phenylcarbamoyl)ferrocene

The reaction of in situ generated 1′-(diphenylphosphino)-1-lithioferrocene with isocyanates RNCO affords the respective phosphino-carboxamides Ph₂PfcCONHR (fc = ferrocene-1,1′-diyl, R = cyclohexyl (2), and Ph (3)) in moderate yields. The coordination behaviour of 3 chosen as a representative was studied in palladium(II) and platinum(II) complexes. Depending on the metal precursor and the reaction conditions, the following compounds featuring this ligand as a P-monodentate or an O,P-chelating donor were isolated and characterised by spectroscopic methods (IR, multinuclear NMR and electrospray ionisation MS): trans-[PdCl₂(3-κP)₂] (5), trans-[PtCl₂(3-κP)₂] (6), cis-[PtCl₂(3-κP)₂] (7), [SP-4-4]-[(L^NC)PdCl(3-κP)] (8; L^NC = 2-[(dimethylamino-κN)methyl]phenyl-κC¹), and [SP-4-3]-[(L^NC)PdCl(3-κ²O,P)]SbF₆ (9). Besides, the crystal structures of a phosphine oxide resulting by oxidation of 2, viz Ph₂P(O)fcCONHCy (4), and of complexes 5·2Et₂O and 9 have been determined by single-crystal X-ray diffraction analysis.