A novel nano-electrospray emitter has been developed containing two separated channels running throughout the length of the emitter. The emitters have been fabricated from "theta-shaped" borosilicate capillaries. Loading of different solutions into the two different channels opens up the possibility to study short timescale interactions within a Taylor cone common to both channels. The common Taylor cone constitutes an extremely small "mixing volume" of the order of femtolitres. The products of electrospray from the dual-channel emitters have been analysed by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Results are presented for interactions of vancomycin with diacetyl-L-lysyl-D-alanyl- D-alanine and interactions of vancomycin with deuterated vancomycin. On the basis of these results, it is concluded that, during electrospray, specific non-covalent adducts have been formed and that there have been exchange reactions involving making and breaking of covalent bonds.

Acetyl and formyl group migration, mutarotation, and hydrolysis of mono-O-acylated glucose are studied by in situ 1D and 2D (1)H NMR spectroscopy. Alpha-D-glucosyl-1-acetate and alpha-D-glucosyl-1-formate serve as sole starting materials. They are generated in situ by configuration retaining glucosyltransfer from alpha-D-glucosyl-1-phosphate to formate and acetate, which is catalyzed by the Glu-237 --> Gln mutant of Leuconostoc mesenteroides sucrose phosphorylase. Temporary accumulated regio-isomeric mono-O-acyl D-glucoses are identified, characterized, and quantified directly from the reaction mixture. Time courses of the transformations give insight into pH dependence of acyl group migration and mutarotation as well as into the stability of various regioisomers.

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Plasmid DNA may exist in three isoforms, the linear, open-circular (oc, "nicked"), and covalently closed circular (ccc, "supercoiled") form. We have recently reported on the chromatographic separation of supercoiled plasmid topoisomers on cinchona-alkaloid modified silica-based stationary phases. Herein, we present a selectivity switching mechanism to achieve separation of isoforms and/or supercoiled topoisomers using the very same chromatographic column and system. While salt gradient elution facilitates topoisomer separation, the supercoiled species are eluting as a single peak upon elution by a mixed pH and organic modifier gradient, still well separated from the other isoforms. We have found that a mobile phase pH value near the pI of the zwitterionic adsorbent surface leads to full recovery of all plasmid DNA isoforms, which is a major issue when using anion exchange-based resins. Furthermore, the observed elution pattern, oc < linear < ccc, is constant upon changes of mobile phase composition, gradient slope, and plasmid size. The remarkable isoform selectivity found on quinine-based selectors is explained by van't Hoff plots, revealing a different binding mechanism between the supercoiled plasmid on one hand and the oc and linear isoforms on the other hand.

We recently discovered the molecular recognition capability of a quinine carbamate ligand attached to silica as a powerful chemoaffinity material for the chromatographic separation of circular plasmid topoisomers of different linking numbers. In this paper we develop structure-selectivity relationship studies to figure out the essential structural features for topoisomer recognition. By varying different moieties of the original cinchonan-derived selector, it was shown that intercalation by the quinoline moiety of the ligand as assumed initially as the working hypothesis is not an essential feature for topoisomer recognition during chromatography. We found that the key elements for topoisomer selectivity are the presence of a rigid weak anion-exchange site and a H-donor site separated from each other in a defined distance by a 4-atom spacer. Additionally, incorporation of the weak anion-exchange site into a cyclic ring structure provides greater rigidity of the ligand molecule and turned out to be advantageous, if not mandatory, for (close to) baseline separation.

Herein, we report on the in vitro change of DNA conformation of plasmids bound to a 3-aminopropyl-modified mica surface and monitoring the events by atomic force microscopy (AFM) imaging under near physiological conditions. In our study, we used an intercalating drug, chloroquine, which is known to decrease the twist of the double helix and thus altered the conformation of the whole DNA. During our experiments, a chloroquine solution was added while imaging a few highly condensed plasmid nanoparticles in solution. AFM images recorded after the drug addition clearly show a time-resolved relaxation of these bionanoparticles into a mixture of loose DNA strands.

Recognizing pDNA supercoils: Differently supercoiled species of the same plasmid DNA can be separated by topology‐selective chromatography. Two‐dimensional HPLC proved that the supercoiling changes during fermentation. Thus, a new quality criterium might help to optimize the effectivity of future genetic drugs and vaccines.

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