Isobutane chemical ionization mass spectra of unsaturated alcohols

Analysis of the isobutane chemical ionization mass spectra of hexenols, cyclohexenols and various syn/anti pairs of bicyclic and tricyclic homoallylic alcohols shows that: (i) the spectra of the allylic alcohols are dominated by [M + H – H₂O]⁺ and [M + C₄H₉–H₂O]⁺ ions and contain traces of [M + H]⁺ ions; (ii) [M + H]⁺ ions are prominent in the spectra of acyclic and certain cyclic homoallylic alcohols; and (iii) [M + H]⁺ ions dominate the spectra of other acyclic unsaturated alcohols. The [M + H]⁺ ions may result from either: (a) protonation of the hydroxyl group, followed by a very rapid intramolecular proton transfer from the protonated hydroxyl group to the carbon–carbon double bond or internal solvation of the protonated hydroxyl group by the carbon–carbon double bond; and/or (b) direct protonation of the carbon–carbon double bond with significant internal solvation of the resulting carbocation by the hydroxyl group, which may lead to carbon–oxygen bond formation to give a protonated cyclic ether. The consequences of placing various geometric constraints on the possible intramolecular interactions between the hydroxyl group and the carbon–carbon double bond in unsaturated alcohols are explored.     

Preparation and electrochemical behavior of dimeric complexes of Ru2(III12, III12) and Ru2(IV,IV) formed by oxidative dimerization of [RuIII(edta)OH2]−

Electrochemical or chemical oxidation of [Ru^III(edta)OH₂]^? proceeds in successive half- and one-electron steps to yield dimeric complexes of Ru(III$\text{1}\text{2}$) and Ru(IV) believed to contain oxo- or dihydroxo-bridging ligands. Spectral and electrochemical properties of the complexes prepared by oxidative dimerization are described and compared with previous reports of dioxygen and peroxo complexes of Ru^III(edta). The dimeric Ru^IV(edta) complex is shown to exhibit modest activity as a catalyst for the oxidation of water to dioxygen.     

Five- and Six-Coordinate 2-Methyl-2-propanethiolato Complexes of Zirconium(IV): Synthesis and Structures of [Li(DME)(3)][Zr(SCMe(3))(5)] and [(THF)Li](2)Zr(SCMe(3))(6)

Five-coordinate and six-coordinate 2-methyl-2-propanethiolato complexes of zirconium, [Li(DME)(3)][Zr(SCMe(3))(5)] (1) and [(THF)Li](2)Zr(SCMe(3))(6) (2), were obtained from the ZrCl(4)/LiSCMe(3) reaction system. The control of the Zr coordination number, by the ether ligands, THF or DME, bound to Li, is demonstrated by the conversion of 2 into 1 upon dissolution in DME. 1 and 2 were crystallographically characterized. The structures are extensively disordered. Crystal data follow: 1, hexagonal P6(3)/m, a = b = 12.496(3) ?, c = 17.561(9) ?, Z = 2, V = 2375(1) ?(3), R = 5.0%, R(w) = 6.8%; 2, trigonal R32, a = b = 11.813(3) ?, c = 28.37(1) ?, Z = 3, V = 3428(1) ?(3), R = 5.2%, R(w) = 6.4%.     

Simultaneous quantification of terpenelactones and flavonol aglycones in hydrolyzed ginkgo biloba extract by liquid chromatography with inline ultraviolet and evaporative light scattering detection

We report here a liquid chromatography (LC) method with inline ultraviolet/evaporative light scattering (UV/ELS) detection for the simultaneous quantification of the terpenelactones and flavonol aglycones in a single sample of hydrolyzed Ginkgo biloba extract (GBE). The sample is hydrolyzed by a rapid and convenient oven heating method for 1 h at 90 degrees C with 10% hydrochloric acid. The 1 h hydrolysis was found to be equivalent to the 2.25 h reflux treatment for dry powder extract, where total flavonol glycosides were 28.4 and 28.1%, respectively. Acceptable precision was achieved for total terpenelactones [relative standard deviation (RSD) = 4.8%] by ELS detection, and total flavonol aglycones (RSD = 2.3%) by UV detection. The analytical range was 1.5 to 7.3% (w/w) for the individual terpenelactones (ELS) and 2.5 to 15.0% (w/w) for the individual glycosides (UV) calculated from the aglycones quercetin, kaempferol, and isorhamnetin. This improved method allows for the first time high throughput sample preparation coupled with the quantification of the predominant compounds generally used for quality control of GBE in a single assay.     

Investigation of bovine ubiquitin conformers separated by high-field asymmetric waveform ion mobility spectrometry: Cross section measurements using energy-loss experiments with a triple quadrupole mass spectrometer

High-field asymmetric waveform ion mobility spectrometry (FAIMS) was used to separate gas-phase conformers of bovine ubiquitin produced by electrospray ionization. These conformers were sampled by a triple quadrupole mass spectrometer where energy-loss experiments, following the work of Douglas and co-workers, were used to determine their cross sections. The measured cross sections for some conformers were readily altered by the voltages applied to the interface ion optics, therefore very gentle mass spectrometer interface conditions were required to preserve gas-phase conformers separated by FAIMS. Cross sections for 19 conformers (charge states +5 through +13) were measured. Two conformers for the +12 charge state, which were readily separated in FAIMS, were found to have similar cross sections. Based on a method to calibrate the collision gas thickness, the cross sections measured using the FAIMS/energy-loss method were compared with literature values determined using drift tube ion mobility spectrometry. The comparison illustrated that the conformers of bovine ubiquitin that were identified using drift tube ion mobility spectrometry were also observed using the FAIMS device.     

Synthesis of a selective estrogen receptor β-modulator via asymmetric phase-transfer catalysis

An efficient asymmetric synthesis of selective estrogen receptor β-modulator (S)-4-bromo-9a-butyl-8-chloro-6-fluoro-7-hydroxy-1,2,9,9a-tetrahydro-fluoren-3-one was developed. The route features a chemoselective aromatic chlorination reaction, an asymmetric phase-transfer-catalyzed alkylation of an indanone with efficient ee upgrade by racemate crystallization, and a robust bromination reaction using imidazole as an in situ bromine trap to avoid overreaction. The synthesis proceeds in 34% yield over 8 steps from 2-fluoroanisole, and provides material with >99.5% ee.     

Analysis of rabbit tear proteins by high-pressure liquid chromatography/electrospray ionization mass spectrometry

The aim of this study was to develop a fast and reliable analytical procedure for the display of the protein components of tears that can be used to differentiate the status of the ocular surface. Using this new procedure, we analyzed the tear protein components following a corneal wound in the rabbit. Calibrated 10-microL glass, fire-polished capillary micropipettes were used to collect tears from New Zealand White rabbits prior to and daily for 9 days following a unilateral 6-mm diameter centrally placed anterior keratectomy. Tear proteins were eluted by a reversed-phase high-performance liquid chromatography (RP-HPLC) column and the tear protein profile was monitored by electrospray ionization (ESI) mass spectrometry positive total ion current (TIC) chromatography. Tear proteins were reliably separated into 17 peaks, each of which contained one or a number of protein components. The molecular weight of each protein component was determined by on-line ESI. Major tear protein components, lactoferrin, lysozyme (minimally detectable in rabbit tears), albumin, lipocalin, lipophilin and beta2-microglobulin, were tentatively identified by this method. Based on the mass spectrometric data, beta2-microglobulin was found to be glycosylated with N-acetylhexosamine. ESI-positive TIC chromatograms and mass spectra revealed comparative differences in the tear protein spectra after corneal wounding. One day after wounding, rabbit lysozyme with a molecular weight of 14,717 Da was found to be 8-fold higher in the tears of wounded eyes when compared with tears from unwounded eyes. It dropped back to normal 3 days after wounding. The expression of an unidentified tear protein with the molecular weight of 16,060 Da was also elevated after corneal wounding and returned to normal level by day 5. In this study, LC/ESI-MS was developed as a fast, reproducible and simple method for the identification and analysis of many of the protein components of the tears. Importantly, this technique also allows quantification of each component resolved in the chromatogram. This method is very suitable for mapping peptides and proteins (<80 kDa) in tears.     

Stereoselectivity of Dienamine [4 + 2] Cycloadditions Synthesis of Functionalised Decalins and Drimanes

The [4 + 2] cycloaddition stereoselectivity of dienamines 1–4 with dimethyl fumarate and fumaronitrile has been investigated, and functionalised decalins 21–40 have been prepared by elimination of Me₂NH from cycloadducts 7–11 and 15–20 ; in the context of the synthesis of drimane sesquiterpenes, the reduction of dienediesters 29 and 30 is also described.     

Diastereoselective synthesis of cyclopropane amino acids using diazo compounds generated in situ

A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using aryl and unsaturated diazo compounds generated in situ from the corresponding tosylhydrazone salts. It was found that thermal 1,3-dipolar cycloaddition followed by nitrogen extrusion gave the cyclopropane amino acid derivatives with good E selectivity, while reactions in the presence of meso-tetraphenylporphyrin iron chloride gave predominantly the corresponding Z isomers. The synthetic utility of this process was demonstrated in the synthesis of (+/-)-(Z)-2,3-methanophenylalanine [(+/-)-(Z)-1], the anti-Parkinson (+/-)-(E)-2,3-methano-m-tyrosine [(+/-)-(E)-2], and the natural product (+/-)-coronamic acid [(+/-)-3].     

Classical and quantum mechanical infrared echoes from resonantly coupled molecular vibrations

The nonlinear response function associated with the infrared vibrational echo is calculated for a quantum mechanical model of resonantly coupled, anharmonic oscillators at zero temperature. The classical mechanical response function is determined from the quantum response function by setting variant Planck's over 2pi-->0, permitting the comparison of the effects of resonant vibrational coupling among an arbitrary number of anharmonic oscillators on quantum and classical vibrational echoes. The quantum response function displays a time dependence that reflects both anharmonicity and resonant coupling, while the classical response function depends on anharmonicity only through a time-independent amplitude, and shows a time dependence controlled only by the resonant coupling. In addition, the classical response function grows without bound in time, a phenomenon associated with the nonlinearity of classical mechanics, and absent in quantum mechanics. This unbounded growth was previously identified in the response function for a system without resonant vibrational energy transfer, and is observed to persist in the presence of resonant coupling among vibrations. Quantitative agreement between classical and quantum response functions is limited to a time scale of duration inversely proportional to the anharmonicity.