Determination of bis-carboxyethyl germanium sesquioxide by gas chromatography with microwave-induced plasma-atomic emission detection after derivatization with alkyl chloroformates

Organic germanium compounds, especially Ge-132, more corrctly denoted as bis-beta-carboxyethyl germanium sesquioxide ([Ge(=O)CH₂CH₂CO₂H]₂O), are of continued interest as they are said to promote health and display anticancer activity. Although these beneficial effects have never been substantiated by comprehensive clinical studies, this drug can still be obtained through various sources and is usually marketed as a nutritional supplementation rather than an anticancer medication. As the quality standards under which this drug is produced are unknown, the need for an effective quality control of these products arises. To date, Ge-132 is considered generally as a safe compound for application in contrast to inorganic germanium which demonstrates severe renal toxicity. In this paper, a new approach to the determination of Ge-132, based on derivatization by ethyl chloroformate reagent (ECF), in the presence of ethanol and pyridine in the mixture, and subsequent analysis by gas chromatography coupled with microwave-induced plasma-atomic emission detection (GC-MIP-AED), is reported. Reaction conditions of the derivatization procedure were optimized with particular respect to the reagent (ECF) and catalyst (pyridine) concentrations. The proposed method is capable of distinguishing Ge-132 from inorganic germanium. The derivatization procedure was also tested with the use of methyl chloroformate (MCF) as alternative reagent, providing interesting additional information about the nature of the final product and the proposed reaction scheme. Among the two types of chloroformates, i.e., MCF and ECF, the latter proved to be more suitable for the proposed method, providing a calibration curve of superior sensitivity and linearity compared with the one obtained with MCF. The method was applied successfully in three real samples, two food supplements, and one commercially available fertilizer. The analysis of the Ge-132 derivative showed good linearity in the concentration of 1–250 mg L^?1 (r ²?=?0.9986) and a satisfactory precision (RSD?=?6.8 %), which qualifies the proposed method for the speciation analysis of Ge in various matrices.     

Methyl 4-toluenesulfonyloxymethylphosphonate, a new and versatile reagent for the convenient synthesis of phosphonate-containing compounds

A straightforward procedure leading to the new phosphonylating reagent, methyl 4-toluenesulfonyloxymethylphosphonate, requiring no chromatographic purification is described. This stable reagent works with the same efficiency as dimethyl and other dialkyl esters for the introduction of an O-phosphonomethyl moiety while, in contrast to dimethyl ester, it does not cause any unwanted methylation of sensitive functionalities. Its utility for the alkylation of protected nucleosides in high yield is exemplified.     

Immobilization in biotechnology and biorecognition: from macro- to nanoscale systems

Biological molecules such as enzymes, cells, antibodies, lectins, peptide aptamers, and cellular components in an immobilized form are extensively used in biotechnology, in biorecognition and in many medicinal applications. This review provides a comprehensive summary of the developments in new immobilization materials, techniques, and their practical applications previously developed by the authors. A detailed overview of several immobilization materials and technologies is given here, including bead cellulose, encapsulation in ionotropic gels and polyelectrolyte complexes, and various immobilization protocols applied onto surfaces. In addition, the review summarises the screening and design of an immobilization protocol, practical applications of immobilized biocatalysts in the industrial production of metabolites, monitoring, and control of fermentation processes, preparation of electrochemical/optical biosensors and biofuel cells.     

Statistical Examination of the <Emphasis Type="Italic">a</Emphasis> and <Emphasis Type="Italic">a</Emphasis> + 1 Fragment Ions from 193 nm Ultraviolet Photodissociation Reveals Local Hydrogen Bonding Interactions

Dissociation of proteins and peptides by 193 nm ultraviolet photodissociation (UVPD) has gained momentum in proteomic studies because of the diversity of backbone fragments that are produced and subsequent unrivaled sequence coverage obtained by the approach. The pathways that form the basis for the production of particular ion types are not completely understood. In this study, a statistical approach is used to probe hydrogen atom elimination from a + 1 radical ions, and different extents of elimination are found to vary as a function of the identity of the C-terminal residue of the a product ions and the presence or absence of hydrogen bonds to the cleaved residue.

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Effect of colloidal particle size on adsorbed monodisperse and bidisperse monolayers

Coating hydrogel films or microspheres by an adsorbed colloidal shell is one synthesis method for forming colloidosomes. The colloidal shell allows control of the release rate of encapsulated materials, as well as selective transport. Previous studies found that the packing density of self-assembled, adsorbed colloidal monolayers is independent of the colloidal particle size. In this paper we develop an equilibrium model that correlates the packing density of charged colloidal particles in an adsorbed shell to the particle dimensions in monodisperse and bidisperse systems. In systems where the molar concentration in solution is fixed, the increase in adsorption energy with increasing particle size leads to a monotonic increase in the monolayer packing density with particle radius. However, in systems where the mass fraction of the particles in the adsorbing solutions is fixed, increasing particle size also reduces the molar concentration of particles in solution, thereby reducing the probability of adsorption. The result is a nonmonotonic dependence of the packing density in the adsorbed layer on the particle radius. In bidisperse monolayers composed of two particle sizes, the packing density in the layer increases significantly with size asymmetry. These results may be utilized to design the properties of colloidal shells and coatings to achieve specific properties such as transport rate and selectivity.     

Synthesis of novel deoxynucleoside S-methylphosphonic acids using S-(diisopropylphosphonomethyl)isothiouronium tosylate, a new equivalent of mercaptomethylphosphonate

The synthesis of the novel nucleotide analogues 5'-deoxynucleoside-5'-S-methylphosphonates, starting from 5'-deoxy-5'-haloribonucleosides, 5'-O-tosylribonucleosides, and 2'-O-triflylnucleosides, is described. The phosphonothiolation of these compounds was achieved using S-(diisopropylphosphonomethyl)isothiouronium tosylate, a new, odourless, and efficient equivalent of mercaptomethylphosphonate. The thiolate anion of mercaptomethylphosphonate was generated in situ from the isothiouronium salt in both protic and aprotic solvents using two equivalents of sodium iso-propoxide. The prepared nucleoside 5'-S-methylphosphonates were deprotected, and the free phosphonic acids were transformed into diphosphoryl derivatives (the NTP analogues). Both mononucleotides and NTP analogues were studied as substrates/inhibitors of several enzymes that are involved in the nucleoside/nucleotide metabolism.     

A simple method for the determination of uranium and thorium by delayed neutron counting

A simple method for the determination of uranium and thorium by delayed neutron counting is described. One portion of the sample is irradiated in a reactor and the delayed neutrons are counted. Another portion of the sample is mixed with B₄ C powder absorbing the thermal neutrons, and irradiated in the same position. From those data, both uranium and thorium can be calculated when a quantitative calibration has been made beforehand. The detection limits for the pure elements are 0.07 ppm for uranium and 2 ppm for thorium with the minimum analyzing time being 2 min. The accuracy of the method is investigated by comparing results obtained by the method described here with results obtained by epithermal activation analysis.