Identification and structural analysis of cereal arabinoxylan-derived oligosaccharides by negative ionization HILIC-MS/MS

Recent works provide evidence of the prebiotic potential of arabinoxylan-derived oligosaccharides (A)XOS. In this study, we developed a structural analysis for cereal-derived (A)XOS by negative ionization HILIC-MS/MS. Initially, we assessed twelve (A)XOS samples of known structures with different linkage positions and branching points by direct-infusion negative ESI-MSn. We subsequently developed the negative ion HILIC-MS/MS with a post-column addition of ammonium chloride. The selected (A)XOS represented both linear (arabinofuranosyl residue linked to the non-reducing end of xylooligosaccharide) and branched structures. Each (A)XOS sample produced a specific spectrum in negative ion ESI-MSn. By analyzing cross-ring fragment ions, we determined the linkage positions of linear (A)XOS. The presence or absence of diagnostic ions in the MS3 allowed us to detect different branches (O-2- or/and O-3-linked arabinofuranosyl with/or without O-4-linked xylopyranosyl at the non-reducing end). Furthermore, we could identify all analyzed samples by HILIC-MS/MS, based on the formed spectral library and chromatographic retention times.Peer reviewe

Low noise amplifiers for MetOp-SG

We present low-noise amplifiers (LNA) that have been developed in the framework of two pre-qualification ESA projects for frequencies between 54 and 229 GHz for the METOP-SG satellite program. The main goal of these satellites is water vapor detection in atmospheric science and weather forecasting which advances the current state of the art for the metamorphic high electron mobility transistor (mHEMT) technology. The MMIC amplifiers are based on the In0.52Al0.48As/In0.8Ga0.2As/In0.53Ga0.47As heterostructure and utilize transistors with a gate length of 50 nm. On-wafer measurements will be presented for all frequency bands as well as results of packaged LNAs

Arabinoksylaanista eristettyjen oligosakkaridien rakenteen selvittäminen moniulotteisella massaspektrometrisella menetelmällä

Tutkielman kirjallisuusosassa käsiteltiin arabinoksylaanin rakennetta ja rakenteen selvittämisessä käytettävien massaspektrometristen menetelmien periaatetta. Lisäksi tarkasteltiin moniulotteisessa massaspektrometriassa tapahtuvaa hiilihydraattirakenteiden hajoamista ja tästä muodostuvien neutraalien fragmenttien ja tuoteionien nimeämistä sekä niistä saatavaa rakennetietoa. Myös oligosakkaridien derivatisointia ja sen vaikutusta rakenteen hajoamiseen tarkasteltiin. Kokeellisessa osassa tutkittiin lineaarisia ksylo-oligosakkarideja ja rakenteeltaan tunnettuja eri tavoin substituoituja arabinoksylaaneja. Tutkituista kuudesta arabinoksylaanista kolme oli haaroittuneita. Massaspektreistä pyrittiin tunnistamaan eri rakenteille ominaisia neutraalifragmentteja ja tuoteioneja. Oligosakkarideja analysoitiin derivatisoimattomina, alditoleina sekä metyloituina alditoleina positiivisella ja negatiivisella ionisaatiolla. Oligosakkaridien derivatisoinnilla pyrittiin muodostamaan erilaisia tuoteioneja ja tarkastelemaan derivatisoinnin merkitystä hajomaismekanismin kannalta. Derivatisoimattomista oligosakkarideista saatiin eniten rakennetietoa negatiivisella ionisaatiolla. Varauksen sijoittuminen oligosakkaridin pelkistävään päähän mahdollisti hajoamistuotteiden systemaattisen tarkastelun. Pelkistetyillä oligosakkarideilla C-ionien alhainen intensiteetti hankaloitti rakenteen selvittämistä. Metyloiduilla alditoleilla oligosakkaridin haaroittuneisuus voitiin selvittää metyloinnin aiheuttaman neutraalifragmenttien painomuutoksen avulla. Metylointi muutti oligosakkaridien rengasrakenteen hajoamismekanismeja ja tuoteionien jakaumia massaspektreissä. C-ionien sijaan metyloituja alditoleja analysoitaessa päädyttiin fragmentoimaan B-ioneja. B-ioneista muodostui metyloiduilla alditoleilla sidostyypeille ominaisia neutraalifragmentteja, joiden avulla oligosakkaridin rakenne voitiin selvittää. Terminaalisen arabinoosisubstituentin sisältäneiden rakenteiden erottaminen lineaarisista rakenteista osoittautui kuitenkin haasteelliseksi.The literature review deals with the structure of arabinoxylan and the principles of mass spectrometric methods used in analyzing them. The fragmentation of carbohydrate structures, the structural information gained from it, and naming of the resulting neutral fragments and product ions was also discussed. The aim of the experimental work was to analyze linear xylo-oligosaccharides and branched or linear arabinoxylans with known structures using tandem mass spectrometry. Of the arabinoxylo-oligosaccharides analyzed, three were branched while the others had an arabinose substituent at terminal xylose. The oligosaccharides were analyzed as underivatized, alditols, and methylated alditols with both positive and negative ionization. Derivatization was done in order to produce different product ions and to gain information about the effect of reduction and methylation on fragmentation mechanisms. Underivatized oligosaccharides provided most information with negative mode ionization. Low intensity of C-type fragment ions prevented their isolation in MS3-step when reduced oligosaccharides were analyzed. Methylation changed the weights of fragmentation products, which made it possible to detect branching in the oligosaccharide structure. Methylation also changed the fragmentation mechanism which caused differences in the product ion spectra compared to underivatized oligosaccharides. B-ions were fragmented to gain information about linkage positions when analyzing methylated alditols. The mechanism of B-ion fragmentation differs from that of C-ions, and produced information rich neutral fragments. However, low signal intensity made branch site analysis difficult, especially when arabinose substituent was located at terminal xylose

Publication I Cathodic electrogenerated chemiluminescence of Ru(bpy) 3 2+ chelate at oxide-coated heavily doped silicon electrodes

Abstract High amplitude cathodic pulse polarization of ultra thin oxide film-coated heavily doped silicon electrodes induces tunnel emission of hot electrons into aqueous electrolyte solution, which probably results in the generation of hydrated electrons in the vicinity of the electrode surface. The method allows the detection of tris (2,2 -bipyridine) ruthenium(II) chelate at subnanomolar concentration level. This paper shows that both n-and p-type heavily doped silicon electrodes can be used, illustrates the effect of oxide film thickness upon the silicon electrode on the intensity of ECL of tris (2,2 -bipyridine) ruthenium(II) and discusses the basic features of tris (2,2 -bipyridine) ruthenium(II) chelatespecific ECL at these electrodes. Thin oxide film-coated silicon electrodes provide a lower blank emission and a higher ECL intensity of the present ruthenium chelate than oxide-covered aluminium electrodes. This suggests that thin oxide film-coated silicon is a very promising working electrode material, especially in microanalytical systems made fully or partly of silicon