Structure elucidation of the thermal degradation products of the nucleotide cofactors NADH and NADPH by nano-ESI-FTICR-MS and HPLC-MS

Redox cofactors like NADH and NADPH are essential for the catalytic activity of several oxidoreductases. Here, we describe a comparative study of the thermal degradation products of both cofactors in the dry and liquid states. The degradation products were first separated, detected, and quantified by high-performance liquid chromatography (HPLC). Subsequently, selected main fractions were investigated by nanoelectrospray ionization–Fourier transform ion cyclotron resonance mass spectrometry (MS). Additionally, HPLC-MS was used to elucidate the structure of all degradation products. From these data, degradation pathways for both the liquid and the solid states were elucidated. Thermal degradation in water is significantly faster compared to degradation in the solid state. Hydrolysis and oxidative ring opening of the reduced nicotinamide adenine dinucleotide (phosphate) were shown to be the main reaction paths. Surprisingly, no significant differences were observed between the degradation of both cofactors in solution and in the solid state. Our results demonstrate that the stability of both cofactors is not limiting at moderate temperatures if they are used in the dry state (e.g., solid/gas catalysis). Significant degradation of dry cofactors was only observed under conditions, which are usually not appropriate for biocatalysis (>95 °C). Besides, the situation is completely different in solution where degradation is already observed at moderate temperatures.     

Monolithic silica-based capillary column with strong chiral cation-exchange type surface modification for enantioselective non-aqueous capillary electrochromatography

A silica-based monolithic stationary phase prepared by the sol-gel process in a 100 microm I.D. fused-silica (FS) capillary has been modified chemically with 3-mercaptopropyl trimethoxysilane followed by immobilization of a strong cation-exchange (SCX) type chiral selector, (S)-N-(4-allyloxy-3,5-dichlorobenzoyl)-2-amino-3,3-dimethylbutane phosphonic acid, by radical addition reaction onto the reactive sulfhydryl surface. After a fine-tuning of the mobile phase composition, the enantioselective capillary column was evaluated for the separation of various chiral basic drugs by enantioselective non-aqueous capillary electrochromatography (CEC), in comparison to capillary column analogs packed with 3.5 microm silica particles having attached the same selector. The performance of the monolithic silica column was further compared to corresponding polymethacrylate-based organic polymer monoliths. The study indicated that strong counter-ions such as 2-aminobutanol or N,N,N',N'-tetramethylethylenediamine are needed, although they reduce the electroosmotic flow velocity and separation factors in comparison to less efficient counter-ions, in order to allow the elution of the oppositely charged solutes in the ion-exchange retention mode within reasonable run time and as sharp zones. In contrast, weak counter-ions such as N,N-diisopropylethylamine (Huenig base) provided stronger electroosmotic flow and much better separation factors, but relatively poor peak efficiencies. Overall, with the chemically functionalized monolithic silica column the high quality separations of packed column analogs could be approximated, with regards to both separation factors and peak performances. On the other hand, the monolithic capillary column certainly outperformed the packed column in terms of system robustness under capillary electrochromatography conditions and showed excellent column longevity. The enantioselective strong cation-exchange-type monolithic silica column performed also well in comparison to the organic polymer monolith.     

BSB5-Bestimmung durch direkte coulometrische Bestimmung des verbrauchten Sauerstoffs

Zusammenfassung In einem geschlossenen System werden 250 ml der Probe zur Bestimmung des Sauerstoffbedarfs thermostatisiert bei 20° C angesetzt. Zu diesem System geh?rt der Anodenraum einer Wasserelektrolyse, die elektrisch gespeist wird mit einem Coulometer, das durch einen Quecksilberschalter, der aufΔp dieses Systems anspricht, gesteuert wird. Im gleichfalls angeschlossenen Natronkalkrohr wird gebildetes CO₂ gebunden. Die Einschaltzeiten des Coulometers werden mit einer mechanisch-elektrischen übertragung und einem mV-Schreiber festgehalten. Die Aufzeichnung stellt die Intensit?t des biologischen Wachstums im Verh?ltnis zur abgelaufenen Zeit dar. Aus dem Gesamtausschlag (mV) kann der Sauerstoffverbrauch nach 5 Tagen errechnet werden.

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Determination of the biochemical oxygen demand (BOD₅) by direct coulometric determination of the oxygen consumed

Summary 250 ml of the sample are given into a closed system thermostatically adjusted to 20° C. This system includes the anodic compartment of a water electrolysis cell connected to a coulometer, which is controlled by a mercury switch responding toΔp of the system. CO₂ is bound in a soda lime tube. The switching times of the coulometer are transmitted to a mV-recorder. Thus the diagram shows the intensity of biological growth in relation to time. The oxygen demand after 5 days can be calculated from the total response.

     

Erhöhte Ausscheidung einer fluoreszierenden Substanz im Harn Ehrlich-Ascites-Tumor tragender Mäuse

Zusammenfassung Im Harn von Ehrlich-Ascites-Tumor tragenden Mäusen wurde eine im Vergleich zum gesunden Tier erhöhte Ausscheidung einer noch nicht identifizierten Substanz durch In-situ-Fluorometrie nach hochspannungselektrophoretischer Trennung gefunden. Eine quantitative Beurteilung der Harnausscheidung erfolgte über die Bildung des Quotienten aus der Fluoreszenzintensität der bei tumortragenden Mäusen erhöhten Bande und der einer benachbarten Referenzbande.

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Increased excretion of a fluorescing substance in the urine of Ehrlich ascites tumor-bearing mice

Summary In the urine of mice bearing Ehrlich ascites tumors, a raised excretion (compared to healthy animals) of a not yet identified substance was found by in-situ fluorimetry after high-voltage electrophoretic separation. The urinary excretion was evaluated quantitatively from the quotient of the fluorescence intensity of the raised bands in the tumor-bearing mice and that of an adjacent reference band.

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Herrn Prof. Dr. Hans Lieb zum 90. Geburtstag gewidmet.     

What a Difference an OH Makes: Conformational Dynamics as the Basis for the Ligand Specificity of the Neomycin‐Sensing Riboswitch

To ensure appropriate metabolic regulation, riboswitches must discriminate efficiently between their target ligands and chemically similar molecules that are also present in the cell. A remarkable example of efficient ligand discrimination is a synthetic neomycin‐sensing riboswitch. Paromomycin, which differs from neomycin only by the substitution of a single amino group with a hydroxy group, also binds but does not flip the riboswitch. Interestingly, the solution structures of the two riboswitch–ligand complexes are virtually identical. In this work, we demonstrate that the local loss of key intermolecular interactions at the substitution site is translated through a defined network of intramolecular interactions into global changes in RNA conformational dynamics. The remarkable specificity of this riboswitch is thus based on structural dynamics rather than static structural differences. In this respect, the neomycin riboswitch is a model for many of its natural counterparts.     

Deconvolution of electrokinetic and chromatographic contributions to solute migration in stereoselective ion-exchange capillary electrochromatography on monolithic silica capillary columns

A monolithic silica stationary phase functionalized with an enantioselective strong cation exchanger based on an aminosulfonic acid derivative was used for chiral separations of basic test solutes by nonaqueous CEC and capillary LC. The effects of the applied electric field as well as the ionic strength in the eluent on electrokinetic and chromatographic contributions to the overall separation performance in the electrically driven mode were investigated. Hence, under the utilized experimental conditions, i. e., at an electric field strength in the range of approximately 120-720 V/cm (applied voltages 4-24 kV) and an ionic strength of the counterion between 5 and 25 mM (at constant acid-to-base, i. e., co- to counterion ratio of 2:1), no deviations from the expected linearity of the EOF were observed. This led to the conclusion that an occurrence of the so-called electrokinetic effects of the second kind resulting from electric double layer overlap inside the mesopores of the monolithic stationary phase and concentration polarization phenomena were largely negligible. Additional support to this conclusion was inferred from the observed independence of CEC retention factors on the electric field strength across the investigated ionic strength range of the BGE. As a consequence, a simple framework allowing for calculation of the CEC mobilities from the individual separation contributions, viz. electroosmotic and electrophoretic mobilities as well as retention factors, could be applied to model CEC migration. There was a reasonable agreement between calculated and experimental CEC mobility data with deviations typically below 5%. The deconvolution of the individual contributions to CEC migration and separation is of particular value for the understanding of the separation processes in which electrophoretic migration of ionic sample constituents plays a significant role like in ion-exchange CEC and may aid the optimization procedure of the BGE and other experimental conditions such as the optimization of the surface chemistry of the stationary phase. In combination with the remarkable column performance evident from the low theoretical plate heights observed under CEC conditions for all test solutes (3.5-7.5 microm in the flow rate range of 0.4-1.2 mm/s, corresponding to (130,000-300,000 plates per meter), the presented framework provides an attractive tool as the basis for the assessment of chromatographic selectivities in a miniaturized CEC screening of new selectors and chiral stationary phases (CSPs), respectively, from experimental CEC data and known CE mobilities.     

Recent accomplishments in the field of enantiomer separation by CEC

The present review intends to summarize recent developments in the field of enantioselective separations and analysis by CEC. It covers studies published in English language in common peer-reviewed journals within the period between 2003 and 2006. Both, methods making use of chiral mobile phase additives as well as chiral stationary phases for electrochromatographic enantiomer separations, are reviewed. Achievements that have been made on the various column technologies, such as open-tubular, particle-packed, inorganic, organic and particle-fixed (hybrid-type) monolithic as well as molecularly imprinted polymer phases, are discussed.