Critical parameters and optimization of a magnesium-selective liquid membrane electrode for application to human blood serum

Summary The selectivity of a new magnesium ionophore (ETH 7025) induced in membranes of different compositions is experimentally studied in view of the ion activities in human serum. The required selectivity coefficient against calcium for the application of an ion-selective magnesium electrode to human serum is calculated for the worst case. Other critical parameters for the application of a liquid PVC-based ion-selective membrane to undiluted human serum discussed are: the sensor lifetime which is related to the lipophilicity of the carrier as well as the ruggedness of the membrane against interactions with components of the relatively lipophilic sample.     

‘Non-Koopmans’ States in Stilbene Cations and a Remarkable Example to the «SDT-Equation»: Indeno [2,1-a]indene

The radical cations of indeno [2, 1-a]indene ( 1 ), stilbene ( 2 ) and 3, 5, 3', 5'-tetramethylstilbene ( 3 ) were prepared by γ-irradiation of the neutral precursors in an electron-scavenging matrix at 77 K . Their electronic spectra were recorded and compared to the photoelectron spectra ( PE .) of the neutral precursors. The results show that either the fourth or the fifth excited doublet state of the cations is of «Non-Koopmans» type, with specific doublet energy (D) D (²B_g)=2.74 eV ( 1 ⁺), =2.59 eV ( 2 ⁺), =2.49 eV ( 3 ⁺). Remarkably, 1 ⁺ possesses two electronic states in the 2.7-2.8 eV energy range: ²A_u («Koopmans»-type) and ²B_g («Non -Koopmans»-type). The «SDT»-equation \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm D} = \sqrt {{\rm S} \cdot {\rm T}} $\end{document} approximately connecting excited singlet (S) and triplet (T) states of a neutral alternant system with the excited doublet (D) states of its radical cation - provided e-promotion occurs For all three excited states between the same (paired) orbitals-is satisfyingly exemplified by 1 : S¹ = 3.92 eV and T¹= 2.06 eV for 1 , D^{4 or 5}=2.74 eV for 1 ⁺.     

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.     

Non-covalent polyvalent ligands by self-assembly of small glycodendrimers: a novel concept for the inhibition of polyvalent carbohydrate-protein interactions in vitro and in vivo

Polyvalent carbohydrate-protein interactions occur frequently in biology, particularly in recognition events on cellular membranes. Collectively, they can be much stronger than corresponding monovalent interactions, rendering it difficult to control them with individual small molecules. Artificial macromolecules have been used as polyvalent ligands to inhibit polyvalent processes; however, both reproducible synthesis and appropriate characterization of such complex entities is demanding. Herein, we present an alternative concept avoiding conventional macromolecules. Small glycodendrimers which fulfill single molecule entity criteria self-assemble to form non-covalent nanoparticles. These particles-not the individual molecules-function as polyvalent ligands, efficiently inhibiting polyvalent processes both in vitro and in vivo. The synthesis and characterization of these glycodendrimers is described in detail. Furthermore, we report on the characterization of the non-covalent nanoparticles formed and on their biological evaluation.     

Gas chromatographic analysis of bifunctional amines after derivatization with methyldichlorophosphine and sulfur

Summary A derivatization procedure for the gas chromatographic analysis of bifunctional amines likeβ-adrenergic blocking drugs is described. The method consists of a two-step reaction with methyldichlorophosphine and sulfur in presence of triethylamine to form cyclic methylphosphonothioic derivatives. The properties of these compounds are discussed and the application of the method to the quantitation of ephedrine in human body fluids is presented. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Determination of gamma-hydroxybutyric acid in human urine by capillary electrophoresis with indirect UV detection and confirmation with electrospray ionization ion-trap mass spectrometry

γ-Hydroxybutyric acid (GHB), a minor metabolite or precursor of γ-aminobutyric acid (GABA), acts as a neurotransmitter/neuromodulator via binding to GABA receptors and to specific presynaptic GHB receptors. Based upon the stimulatory effects, GHB is widely abused. Thus, there is great interest in monitoring GHB in body fluids and tissues. We have developed an assay for urinary GHB that is based upon liquid–liquid extraction and capillary zone electrophoresis (CZE) with indirect UV absorption detection. The background electrolyte is composed of 4 mM nicotinic acid (compound for indirect detection), 3 mM spermine (reversal of electroosmosis) and histidine (added to reach a pH of 6.2). Having a 50 μm I.D. capillary of 40 cm effective length, 1-octanesulfonic acid as internal standard, solute detection at 214 nm and a diluted urine with a conductivity of 2.4 mS/cm, GHB concentrations ≥2 μg/ml can be detected. Limit of detection (LOD) and limit of quantitation (LOQ) were determined to be dependent on urine concentration and varied between 2–24 and 5–60 μg/ml, respectively. Data obtained suggest that LOD and LOQ (both in μg/ml) can be estimated with the relationships 0.83 κ and 2.1 κ, respectively, where κ is the conductivity of the urine in mS/cm. The assay was successfully applied to urines collected after administration of 25 mg sodium GHB/kg body mass. Negative electrospray ionization ion-trap tandem mass spectrometry was used to confirm the presence of GHB in the urinary extract via selected reaction monitoring of the m/z 103.1→m/z 85.1 precursor–product ion transition. Independent of urine concentration, this approach meets the urinary cut-off level of 10 μg/ml that is required for recognition of the presence of exogenous GHB. Furthermore, data obtained with injection of plain or diluted urine indicate that CZE could be used to rapidly recognize GHB amounts (in μg/ml) that are ≥ 4 κ.     

Surface plasmon resonance spectroscopy and quartz crystal microbalance study of streptavidin film structure effects on biotinylated DNA assembly and target DNA hybridization

Surface plasmon resonance (SPR) spectroscopy is employed for the study of biotinylated DNA assembly on streptavidin modified gold surfaces for target DNA hybridization. Two immobilization strategies are involved for constructing streptavidin films, namely, (1) physical adsorption on biotin-containing thiol treated surfaces through biotin-streptavidin links and (2) covalent attachment to 11-mercaptoundecanoic acid (MUA) treated surfaces through amine coupling. To understand the structural properties of the streptavidin films, a quartz crystal microbalance with energy dissipation monitoring (QCM-D) is used to monitor the streptavidin immobilization procedures. The simultaneously measured frequency (Deltaf) and dissipation factor (DeltaD) changes, together with the SPR angle shifts (Deltatheta), suggest that the streptavidin film assembled on the biotin-containing surface is highly rigid with a well-ordered structure while the streptavidin film formed through amine coupling is highly dissipative and less structured. The subsequent biotinylated DNA (biotin-DNA) assembly and target hybridization results show that the streptavidin film structure has distinct effects on the biotin-DNA binding amount. On the streptavidin matrix, not only the probe DNA density but also the strand orientation mediated by the streptavidin films has distinct effects on hybridization efficiency. Particularly, the molecularly ordered streptavidin films formed on the biotin-containing surfaces ensure a well-ordered DNA assembly, which in turn allows for a higher efficiency in target DNA capture and for a higher sensitivity in the hybridization analysis when compared to the biotin-DNA assembled on the less structured streptavidin films formed through amine coupling.