Molecular beam study of photoionization of uranium and uranium oxide

Crossed laser molecular beam configuration was used to study the photoionization of U and UO by the UV-lines of an argon ion laser. Photoionization efficiencies of both U and UO were found to be line sensitive. Photoionization by the 3638 Å line was observed for the first time. Uranium atom ionization efficiency being higher for the 3345 Å and 3511 Å groups of lines, while UO ionization efficiency being maximum for the 3638 Å line. Dependence of photoion signal on laser power and relative photoionization efficiencies of the two isotopic species of uranium are also investigated.     

Neoglycoconjugates from synthetic tetra- and hexasaccharides that mimic the terminus of the O-PS of Vibrio cholerae O:1, serotype Inaba

A glycosyl acceptor and a glycosyl donor having the N-3-deoxy-L-glycero-tetronic acid side chain already attached have been prepared and used for the synthesis of the di-through to the hexasaccharide that mimic the upsteam terminus of the O-specific polysaccharide of Vibrio cholerae O:1, serotype Inaba. The target tetra- and the hexasaccharide, which were obtained in the form of 5-methoxycarbonylpentyl glycosides, were linked to BSA using squaric acid diester chemistry. The conjugation reactions were monitored by surface enhanced laser desorption ionization-time of flight mass spectrometry (SELDI-TOF MS). This allowed the progression of the conjugation of the synthetic oligosaccharides in a controlled way and termination of the reaction when the desired molar hapten/BSA ratio had been reached, yielding neoglycoconjugates with predetermined carbohydrate/carrier ratios. The ability to monitor the conjugation by the SELDI-TOF MS technique made it possible to prepare, from one hapten in a one-pot reaction, several neoglycoconjugates having different, predetermined carbohydrate/carrier ratios.     

Studies towards a Conjugate Vaccine for Anthrax: Synthesis of the Tetrasaccharide Side Chain of the Bacillus anthracis Exosporium

The first synthesis of β‐L ‐glycoside 17 of the tetrasaccharide β‐Ant‐(1 → 3)‐α‐L ‐Rhap‐(1 → 3)‐α‐L ‐Rhap‐(1 → 2)‐L ‐Rhap is described (Schemes 1–3). Its spacer can be functionalized to make it amenable to conjugation to proteins by different conjugation methods. The synthesis was performed in a stepwise manner starting from the aglycon‐bearing terminal saccharide with thioglycosides as glycosyl donors. To attach the upstream terminal anthrose residue, the assembled linker‐equipped trisaccharide was glycosylated with ethyl 4‐azido‐3‐O‐benzyl‐2‐O‐(bromoacetyl)‐4,6‐dideoxy‐1‐thio‐β‐D ‐glucopyranoside ( 11 ). Further functionalization of the tetrasaccharide thus obtained, followed by deprotection gave the target substance 17 . Synthesis of substructures of 17 equipped with the same spacer, namely β‐L ‐Rhap‐1‐O‐(CH₂)₅COOMe ( 21 ), α‐L ‐Rhap‐(1 → 2)‐β‐L ‐Rhap‐1‐O‐(CH₂)₅COOMe ( 22 ), and α‐L ‐Rhap‐(1 → 3)‐α‐L ‐Rhap‐(1 → 2)‐β‐L ‐Rhap‐1‐O‐(CH₂)₅COOMe ( 23 ), is also described (Scheme 4).     

Systematic trends in optogalvanic signals of some transitions in a uranium hollow cathode discharge

A study of optogalvanic (OG) signals in a uranium hollow cathode discharge using a tunable pulsed dye laser with intensities above saturation revealed certain systematic trends. The peaks of OG signals, for a given hollow cathode current, due to all transitions involving the ground state are within a certain range of values. The same is true of the OG signals due to transitions involving the 620 cm^-1 and 3800 cm^-1 lower metastable levels. For all transitions involving the same lower state, the peaks of OG signal vary linearly with the discharge current. The slopes of such straight lines are different for transitions involving different lower levels of uranium. Effects of radiation trapping are seen in the OG signals due to transitions involving the ground state of uranium at currents above 60 mA. Details of our observations are presented and discussed.     

Isotope shift studies and electronic configuration assignments to the energy levels of neutral erbium

Isotope shifts ΔT (170-166) have been evaluated for 54 even and 94 odd energy levels covering almost all the known configurations of the neutral erbium. These ΔT values have been derived from the isotope shift measurements carried out in 159 lines in the region 3900–4605 A using a Fabry-Perot spectrometer and liquid-air-cooled hollow cathode source with highly enriched ¹⁷⁰Er and ¹⁶⁶Er isotopic samples. Electronic configurations assigned to energy levels of Er I by earlier workers have been mostly confirmed and in few cases revisions have been suggested on the basis of observed ΔT values. Probable configurations have been also suggested for unassigned levels of Er I, and a large number of even levels could be assigned to 4f¹¹ 5d 6s 6p configuration.     

Posaconazole (Noxafil, SCH 56592), a new azole antifungal drug, was a discovery based on the isolation and mass spectral characterization of a circulating metabolite of an earlier lead (SCH 51048)

Posaconazole (SCH 56592) is a novel triazole antifungal drug that is marketed in Europe and the United States under the trade name 'Noxafil' for prophylaxis against invasive fungal infections. SCH 56592 was discovered as a possible active metabolite of SCH 51048, an earlier lead. Initial studies have shown that serum concentrations determined by a microbiological assay were higher than those determined by HPLC from animals dosed with SCH 51048. Subsequently, several animals species were dosed with (3)H-SCH 51048 and the serum was analyzed for total radioactivity, SCH 51048 concentration and antifungal activity. The antifungal activity was higher than that expected based on SCH 51048 serum concentrations, confirming the presence of active metabolite(s). Metabolite profiling of serum samples at selected time intervals pinpointed the peak that was suspected to be the active metabolite. Consequently, (3)H-SCH 51048 was administered to a large group of mice, the serum was harvested and the metabolite was isolated by extraction and semipreparative HPLC. LC-MS/MS analysis suggested that the active metabolite is a secondary alcohol with the hydroxyl group in the aliphatic side chain of SCH 51048. All corresponding monohydroxylated diastereomeric mixtures were synthesized and characterized. The HPLC retention time and LC-MS/MS spectra of the diastereomeric secondary alcohols of SCH 51048 were similar to those of the isolated active metabolite. Finally, all corresponding individual monohydroxylated diasteriomers were synthesized and evaluated for in vitro and in vivo antifungal potencies, as well as pharmacokinetics. SCH 56592 emerged as the candidate with the best overall profile.     

Structure elucidation of everninomicin-6, a new oligosaccharide antibiotic, by chemical degradation and FAB-MS methods

The structural characterization of a new oligosaccharide antibiotic, Everninomicin-6 (EV-6), is described. Detailed fast-atom bombardment mass spectrometry (FAB-MS) studies along with NMR and chemical degradation methods were conducted to elucidate the structure of EV-6. The effects of the use of various matrices, including salt addition, on the quality of the FAB-MS were explored. The use of 3-nitro benzyl alcohol, dimethyl sulfoxide (DMSO), and NaCl produced the best results: an intense sodiated molecular ion plus structurely informative fragmentation. FAB-MS yields information providing the complete sugar sequence information for everninomicins, which is quite valuable to the elucidation of the structure of this complex oligosaccharide antibiotic. In addition, the results of accurate mass work with the molecular ion are consistent with the assigned structure. The use of electrospray ionization mass spectrometry (ESI-MS) and ESI-MS/MS for the study of EV-6 was investigated and was found to produce an abundant molecular ion with limited structural information. These results revealed that EV-6 resembled EV-D quite closely except for the absence of the nitrosugar and the replacement on ring g of the -CH₂OCH₃ group with a -CH₂OH group.