Intriguing Mass Spectrometric Behavior of Guanosine Under Low Energy Collision-Induced Dissociation: H<Subscript>2</Subscript>O Adduct Formation and Gas-Phase Reactions in the Collision Cell

An in-depth study of the fragmentation pathway of guanosine was conducted by using an in-source collision-induced dissociation high-mass accuracy tandem mass spectrometry experiment. The equivalent of MS4 data, a level of information normally achieved on ion trap instruments, was obtained on a Q-TOF mass spectrometer. The combination of the features of high-resolution, accuracy, and in-source CID permitted the unambiguous elucidation of the different fragmentation pathways. Furthermore the elemental compositions of the product ions generated were assigned and their mutual genealogical relationships established. Formerly proposed dissociation pathways of guanosine were revisited and elaborated on more deeply. Furthermore, the presence of H2O in the collision cell of several tandem MS instruments was demonstrated and its effect on the product ion spectra investigated. The neutral gain of H2O by particular fragments of guanosine was experimentally proven by using argon, saturated with H2(18)O, as the collision gas. Data indicating the occurrence of more complex reactions in the collision cell as a result of the presence of H2O were produced, specifically relating to neutral gain/neutral loss sequences. In silico calculations supported the experimental observation of neutral gain by guanosine fragments and predicted a similar behavior for adenosine. The latter was subsequently experimentally confirmed.     

A Thermodynamic Analysis of Nonequilibrium Argon Plasma Torches

The nonequilibrium process of argon plasma torches is analyzed theoretically. Thermodynamic diagrams of different degrees of ionization are developed to aid in understanding and analyzing the transition from chemical equilibrium to frozen flow in dc plasma torch operations. A thermodynamic model is developed to describe the nonequilibrium processes in a dc argon plasma torch. In the model the ionization process is approximated as a constant-pressure heating process, with little deviation from the equilibrium state upon completion of heating. If the plasma flow is frozen shortly after heating, the entropy increase is small during the transition from equilibrium to frozen flow. In this case the frozen flow will have nearly the same composition and entropy as the flow at the heating section exit. For singly ionized argon plasmas in the entropy range relevant to dc torch operation, the frozen flow solutions on the affinity–pressure diagram are found to be insensitive to entropy change. Therefore the present model predicts that argon plasmas generated at different power levels will have almost identical affinity at the torch exit for the same operating pressure. This prediction agrees with experimental observations except for very low torch power levels.     

The determination of zirconium and aluminium in alloys slags and fumes by 14-mev neutron activation analysis

Aluminium and zirconium have beendetermined in alloys, slags and fumes by 14-MeV neutron activation analysis. Nuclear reactions with zirconium have been investigated, and the radioisotopes produced by 14-MeV neutron activation have been determined. The results for alloys and slags agree well with those obtained by chemical methods; precisions of 1.8% were obtained in ideal cases. The neutron activation method is capable of analysing 10–12 samples, in duplicate, per man-day.     

The use of split-sample design for performance evaluation of screening kits

Laboratory medicine is an important discipline in health care with its remarkable effect on risk assessment, diagnosis of health, and disease state. This accounts describes a newborn screening approach involving retest, recall, and follow-up procedures. This real life trial emphasizes the need for split-sample design evaluation of newly opened test kits. Quantitative measurements of phenylalanine and neonatal thyroid stimulating hormone (nTSH) were performed in two laboratories. After validation of the calibration in the laboratory that was using the industrially prepared screening kits for the first time, the same real newborn blood spot samples were analyzed for phenylalanine and nTSH measurements in both laboratories and the results obtained were compared non-parametrically, and examined by Deming regression and difference plots. There was no problem with the phenylalanine results: similar results were obtained for the same blood spot cards in both laboratories (P=0.496; bias estimation 0.13). However, the nTSH values were found to be significantly higher in the laboratory that used the nTSH kit for the first time. Although the validation of the calibration of the nTSH kit was valid with the manufactures control materials, spilt-sample results showed that there was a significant difference between the two laboratories (P=0.005; bias estimation 28.6). This study implies that acceptable comparability of split-sample design analysis is needed for testing the analytical performance of industrially prepared tests kits, and this can only be achieved with certified reference materials.Presented at the 8th Conference on Quality in the Spotlight, 17–18 March 2003, Antwerp, Belgium     

Structural characterization of melphalan modified 2′-oligodeoxynucleotides by miniaturized LC-ES MS/MS

In this study a miniaturized LC coupled to electrospray tandem mass spectrometry was used to analyze modifications originating from the interaction between the chemotherapeutic agent melphalan and 2'-oligodeoxynucleotides. Low energy CAD product ion spectra gave information about the specificity of melphalan alkylation with regard to certain DNA sequences. These data can be very useful to estimate the risk in the development of secondary leukaemia as a result of a melphalan cure. In the study of the interaction between melphalan and d(GG), differentiation could be made between alkylation on the 5'-side and alkylation on the 3'-side, because of the presence or absence of the alkylated w1 fragment in the low energy CAD spectra. In the other di-mers alkylation specificity for the different bases could be observed. Melphalan alkylation occurs in the sequence G > A > C > T. The study of the alkylated d(GGGG) revealed the presence of mainly 5'-end alkylation. Furthermore studies were performed which investigated other melphalan treated di-, tetra-, hepta-, and octa-mers.     

Implementation of data-dependent acquisitions in the study of melphalan DNA adducts by miniaturized liquid chromatography coupled to electrospray tandem mass spectrometry

The study of defects in DNA caused by xenobiotics, more particularly the study of DNA adducts, is an important field in cancer aetiology. The analysis of low abundance DNA adducts formed in vivo both in animals and humans requires the development and implementation of highly sensitive analytical methods. Since only a minute amount of DNA can be isolated (ca. 100 microg) it is evident that the amount of sample consumed per analysis should be as small as possible in order to gather as much analytical information as possible. In this article an example is given of how this problem can be solved by the implementation of data-dependent acquisitions using capillary liquid chromatography coupled to electrospray tandem mass spectrometry. As a case study the alkylation of DNA by melphalan is presented. Slight modifications of the chromatographic conditions (mobile and stationary phases) can allow the automated analysis of other kinds of DNA adducts.     

Synthesis of 1-substituted-6-methyluracils

A series of 6-methyl-1H-pyrimidin-2,4-diones bearing different substituents in the 1-position of the uracil ring were prepared starting from substituted ureas and diketene.     

Pore morphology of porous polymer particles probed by NMR relaxometry and NMR cryoporometry

The pore size distribution (PSD) and pore connectivity (PC) within porous polymer particles are probed by combining NMR cryoporometry and NMR relaxometry (spin-spin relaxation). With water as a probe molecule, the constant K in the so-called Gibbs-Thompson equation and the surface relaxivity (rho2) were determined to be K = (420 +/- 50) KA and rho2 = (0.44 +/- 0.01) x 10(-6) ms(-1), respectively. Also, the thickness of the interface layer was estimated to be of the order of one monolayer of water molecules. A detailed analysis of the complete set of NMR data enabled the morphology or pore structure to be probed, and is thoroughly discussed in the text.     

1,5-dimethyl-6H-pyridazino[4,5-b]carbazole,a 3-aza bioisoster of the antitumor alkaloid olivacine

A series of b-fused carbazoles structurally related to pyrido[4,3-b]carbazole-type alkaloids was prepared, utilizing the Diels-Alder reaction of 1-methylpyrano[3,4-b]indol-3(9H)-one with electron-deficient acetylenic dienophiles as the key step. The title compound (14) thus obtained in only four steps represents a new 3-aza analog of the antitumor natural product, olivacine.     

Exploration of cellulose surface-binding properties of Acidothermus cellulolyticus Cel5A by site-specific mutagenesis

Understanding the interactions between cellulases and cellulosic substrates is critical to the development of an efficient artificial cellulase system for conversion of biomass to sugars. We directed specific mutations to the interactive surface of the Acidothermus cellulolyticus EI endoglucanase catalytic domain. The cellulose-binding domain is not translated in these mutants. Amino acid mutations were designed either to change the surface charge of the protein or to modify the potential for hydrogen bonding with cellulose. The relationship between cellulase-to-cellulose (Avicel PH101) binding and hydrolysis activity was determined for various groupings of mutations. While a significant increase in hydrolysis activity was not observed, certain clusters of residues did significantly alter substrate binding and some interesting correlations emerged. In the future, these observations may be used to aid the design of endoglucanases with improved performance on pretreated biomass.