Development of solid phase reactors for continuous detection systems

Summary The methodical development of a solid phase reactor (SPR) as an integrated part of a chemical reaction detector is described for manganese. The preparation of a suitable reactor packing material byin situ precipitation of lead-dioxide on silica gel permits running the SPR in low pressure ranges. Divalent manganese and also higher oxidation states of the metal are oxidized to permanganate in the reactor. Thus, an isoformation of all manganese species originally present in the sample takes place. As the direct photometrical detection of permanganate is not sensitive enough for trace analyses, the heterogeneous oxidation system is followed by a homogeneous chemical reaction system, in which permanganate reacts with leucomalachite green. The resulting blue-green dye is detected photometrically at 620 nm.The application of a column switching technique allows the continuous enrichment, separation, and determination of manganese down to the nanogram level with high precision and also a differentiation between divalent manganese and three- to seven- valent manganese.This chemical reaction detector can be used also for continuous detection in chromatography, especially HPLC. The detection limit is 10 ng/ml.

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Entwicklung eines Festbettreaktors für kontinuierliche Nachweissysteme. Teil I

Zusammenfassung Die methodische Entwicklung eines Festbettreaktors als integrierter Bestandteil eines chemischen Reaktionsdetektors wird beschrieben. Die Herstellung einer geeigneten Reaktorpackung durch Ausfällen von Bleidioxid auf Kieselgel erlaubt den Betrieb des Festbettreaktors im Niederdruckbereich. Zweiwertiges Mangan sowie höhere Oxydationszustände des Metalls werden im Reaktor zum Permanganat-Ion oxydiert, so daß eine Isoformierung aller in der Probe vorhandenen Mangan-Spezies stattfindet. Da die photometrische Detektion des Permanganat-Ions für spurenanalytische Messungen nicht ausreichend empfindlich ist, wird im Anschluß an den heterogenen Bleidioxid-Reaktor ein homogenes chemisches Reaktions-system betrieben, in dem das Permanganat-Ion mit Leukomalachitgrün umgesetzt wird. Dabei entsteht der blaugrüne Farbstoff Malachitgrün, der bei 620 nm photometrisch gemessen wird.Die Verwendung einer Säulenschalttechnik ermöglicht eine kontinuierliche Anreicherung, Abtrennung und Bestimmung von Manganspuren bis in den Nanogramm-Bereich mit hoher Genauigkeit, sowie eine Differenzierung zwischen zweiwertigen Mangan-Spezies einerseits und dreibis siebenwertigen Oxydationsstufen andererseits.Der vorgestellte chemische Reaktionsdetektor kann auch zur kontinuierlichen Chromatographie-Detektion benutzt werden. Die Nachweisgrenze beträgt 10 ng/ml.

     

Direct high-performance liquid chromatographic separation of unusual secondary amino acids and a comparison of the performances of Chirobiotic T and TAG columns

Two macrocyclic glycopeptide antibiotic-type chiral stationary phases (CSPs) based on native teicoplanin and teicoplanin aglycone, Chirobiotic T and TAG, respectively, were evaluated with regard to the high-performance liquid chromatographic separation of the enantiomers of 10 secondary alpha-amino acids (imino acids). The chromatographic results are given as the retention, separation and resolution factors, together with the enantioselective free energy difference corresponding to the separation of the enantiomers. By application of these two CSPs, excellent resolutions were achieved for the investigated compounds by using reversed-phase mobile mode systems. The separation conditions were optimized by variation of the mobile phase composition. The difference in enantioselective free energy between the aglycone CSP and the teicoplanin CSP for these particular amino acids ranged between 0.70 and -1.83 kJ mol(-1). It was established that better enantioseparations of the secondary alpha-amino acids were attained in most cases on the aglycone CSP.     

LC Enantioseparation of β-Lactam and β-Amino Acid Stereoisomers and a Comparison of Macrocyclic Glycopeptide- and β-Cyclodextrin-Based Columns

Direct reversed-phase high-performance liquid chromatographic methods were developed for the separation of the enantiomers of tricyclic β-lactams, cis-3,4-benzo-6-azabicyclo[3.2.0]heptan-7-one, cis-4,5-benzo-7-azabicyclo[4.2.0]-octan-8-one, cis-5,6-benzo-8-azabicyclo[5.2.0]nonan-9-one and new bicyclic β-amino acids, the six- and seven-membered homologues of cis-1-amino-4,5-benzocyclopentane-2-carboxylic acid (benzocispentacin), cis-1-amino-5,6-benzocyclohexane-2-carboxylic acid and cis-1-amino-6,7-benzocycloheptane-2-carboxylic acid. The direct separations of the analytes were performed on chiral stationary phase (CSP) columns containing the macrocyclic glycopeptide antibiotic teicoplanin (Chirobiotic T), teicoplanin aglycone (Chirobiotic TAG), vancomycin (Chirobiotic V), vancomycin aglycone (Chirobiotic VAG), ristocetin A (Chirobiotic R) or a new dimethylphenyl carbamate-derivatized β-cyclodextrin-based Cyclobond DMP. The results achieved with the different methods were compared in systematic chromatographic examinations. The effects of an organic modifier and of the mobile phase composition on the separation and the separation efficiency of different columns were investigated. The difference in enantioselective free energy between the aglycone CSP and the teicoplanin CSP for these β-lactams and β-amino acids ranged between 0.3 and −1.1 kJmol⁻¹. Better enantioseparations were attained in most cases on the aglycone CSP.

     

Gaunt factors for free-free transitions in the fields of positive ions of carbon,nitrogen, and oxygen,calculated in the scaled thomas-fermi approximation

For air plasmas of higher temperature (1.5–2.5 eV) at normal pressure an essential part of the continuous opacity in the visible and near ultraviolet region is generated by free-free transitions of electrons in the fields of positive ions of carbon, nitrogen, and oxygen. Since the hydrogenic approximation leads to values for the thermally averaged Gaunt factor which are significantly too low, calculations are performed by means of the Scaled Thomas-Fermi approximation and compared with other theoretical results.     

Comparison of low-order multireference many-body perturbation theories

Tests have been made to benchmark and assess the relative accuracies of low-order multireference perturbation theories as compared to coupled cluster (CC) and full configuration interaction (FCI) methods. Test calculations include the ground and some excited states of the Be, H(2), BeH(2), CH(2), and SiH(2) systems. Comparisons with FCI and CC calculations show that in most cases the effective valence shell Hamiltonian (H(v)) method is more accurate than other low-order multireference perturbation theories, although none of the perturbative methods is as accurate as the CC approximations. We also briefly discuss some of the basic differences among the multireference perturbation theories considered in this work.     

Simple and condensed β-lactams-I : The application of diketene in β-lactam synthesis. The synthesis and functional group manipulations of diethyl 3-acetyl-4-oxoazetidine-2,2-dicarboxylates

Acylation of the N-substituted diethyl aminomalonates 3a–3d with diketene furnished the ring tautomers 6a–6d of the expected acetoacetyl derivatives 5. By treatment with iodine and sodium ethoxide compounds 6a–6d are smoothly converted into the β-lactam derivatives 2a–2d. Deethoxycarbonylation of the ethylene ketals 7a–7d of the latter furnishes mixtures of the corresponding diastereomeric monoesters 8 and10. The ethoxycarbonyl groups of the trans esters 8 are more reactive than those of the cis isomers 10. This permits, under appropriate conditions, selective alkaline hydrolysis and NaBH₄ reduction of the trans esters 8 in the presence of the cis esters 10. Reduction of the cis ester 10c under more forceful conditions furnishes the trans hydroxymethyl derivative 11c.     

An Ω(n 4/3) lower bound on the randomized complexity of graph properties

We improve King's (n ^5/4) lower bound on the randomized decision tree complexity of monotone graph properties to (n ^4/3). The proof follows Yao's approach and improves it in a different direction from King's. At the heart of the proof are a duality argument combined with a new packing lemma for bipartite graphs.The paper was written while the author was a graduate student at the University of Chicago and was completed at M.I.T. The work was supported in part by NSF under GRANT number NSF 5-27561, the Air Force under Contract OSR-86-0076 and by DIMACS (Center for Discret Mathematics and Theoretical Computer Science), a National Science Foundation Science and Technology Center-NSF-STC88-09648.     

Identification of dinucleoside polyphosphates by matrix-assisted laser desorption/ionisation post-source decay mass spectrometry

Dinucleoside polyphosphates are a group of intra- and extracellular mediators controlling numerous physiological functions. In this study dinucleoside polyphosphates were examined by positive ion matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MADLI-TOFMS). 3-Hydroxypicolinic acid was used as UV-absorbing matrix. For the individual dinucleoside polyphosphates Ap(n)A (n = 2-7), Ap(n)G (n = 2-6) and Gp(n)G (n = 2-6), MALDI post-source decay (PSD) mass spectra were measured. Each mass peak in the MALDI-PSD mass spectra could be assigned to individual fragments of dinucleoside polyphosphates. The comparison of the fragmentation patterns of the dinucleoside polyphosphates presented here demonstrates that dinucleoside polyphosphates preferably cleave to fragment ions consisting of the corresponding mononucleoside polyphosphates as well as the corresponding nucleosides and bases during flight in the field-free drift path of the MALDI mass spectrometer. Therefore, the MALDI-PSD approach described here is suitable for identification of other dinucleoside polyphosphates. The present MALDI-PSD mass spectra may be used as MALDI-PSD mass reference spectra for future identification of dinucleoside polyphosphates and other nucleotides.     

Neue Moleküle A4B3 im System P4Se3–As4Se3

Novel A₄B₃ Molecules in the System P₄Se₃–As₄Se₃ By means of ³¹P-NMR and masspectroscopic measurements in the system P₄Se₃–As₄Se₃ was shown that in the melt and vapour phase at all compositions molecules of the type P_{4 ? n}As_nSe₃ are formed. A separation was possible by liquid chromatography (RP 18-column). The concentration distribution of the different species is nearly statistical. In the solid state at ambient temperature regions of solid solubility with α-P₄Se₃, α⁺-phase, α-P₄S₃ and α-As₄Se₃ structure were observed. P₃AsSe₃ could be transformed into a plastically-crystalline phase with β-P₄S₃ structure. At higher temperatures the phase decomposes slowly. The thermal behaviour of PAs₃Se₃ is strongly influenced by the heating rate. Using low heating rates it decomposes into an amorphous phase, by fast heating a transformation into a metastable plastically-crystalline modification was achieved. During long extraction with CS₂ molecules P_{4 ? n}As_nS_{3 ? m}Se_m are formed by an exchange reaction. They can also be prepared by melting the proper amounts of the elements.