Applications of Gas Chromatography-Mass Spectrometry to Organic Chemistry

The work described in this thesis was based on applications of the combined technique of gas chromatography-mass spectrometry (GC-MS) to a variety of topics in organic chemistry and biochemistry. The research included studies of the scope of the technique (based on model compounds) and applications to actual analytical problems. Following the introduction, a section of the thesis is devoted to work on steroids. Results obtained with progesterone and testosterone analogues confirm The value of GC-MS in distinguishing isomers. The use of trimethylsilyl (TMS) ether derivatives in GC-MS is well established, but the advantages of (chloromethyl)dimethylsilyl ethers as derivatives for GC-MS have been little explored. The utility of these derivatives is illustrated and discussed for the example of 1/alpha-alkyl-17beta-hydroxy steroids. The mass spectral fragmentations of TMS ether derivatives of androst-5-en-3beta-ol analogues and of other unsaturated 3beta-hydroxy steroids have been investigated. The results of this survey have been applied to the characterisation of yeast sterols, sterols from a bacterium (Methylococcus capsulatus) grown on methane, steroidal drug metabolites, and a steroidal enzyme-reduction product. Corticosteroids cannot be examined directly by GC-MS because of References cited in this summary are restricted to publications incorporating work described in the thesis. the low thermal stability of the side chain. Earlier work has shown that their boronate derivatives are quite stable. The mass spectra (recorded by GC-MS) of representative corticosteroid boronates are discussed in respect of their use in structural assignments. Similar difficulties are encountered in GC-MS of beta-hydroxy amines because of their relatively high polarity and low thermal stability. The use of boronate derivatives in the characterisation of catecholamines and related beta-hydroxy amines by GC-MS is discussed, and a more detailed investigation of the mass spectral fragmentations of the derived 1,3,2-oxazaborolidines has been carried out. O-methyloxime (MO) derivatives are of value in the analysis by GC-MS of aldehydes and ketones. Salient features of the spectra of MO derivatives of aliphatic aldehydes and ketones are enumerated. Aldehydes from the cuticular leaf waxes of Chenopodium album L. and Lolium perenne L. have been identified by GC-MS of their MO derivatives. Unsaturated aliphatic hydrocarbons from the green form of the freshwater alga Botryococcus braunii have been ozonised and cleaved to form aldehydes which have been identified as their MO derivatives. The structures of the hydrocarbons have thus been inferred. An exploratory study of the use of GC-MS in the analysis of air pollutants has been carried out. The gas chromatographic and mass spectrometric properties of some polycyclic aromatic hydrocarbons have been surveyed and a number of these compounds have been tentatively identified in dust collected from air conditioner filters. Perfluorodecalin has been found to be a convenient mass calibration standard for low resolution mass spectra. The need for, and problems associated with, computer-assisted data handling in GC-MS are discussed. The development of an on-line real-time data acquisition system is described

Searching for Pulsars in Close Binary Systems

We present a detailed mathematical analysis of the Fourier response of binary pulsar signals whose frequencies are modulated by circular orbital motion. The fluctuation power spectrum of such signals is found to be \nu_orb-periodic over a compact frequency range, where \nu_orb denotes orbital frequency. Subsequently, we consider a wide range of binary systems with circular orbits and short orbital periods, and present a Partial Coherence Recovery Technique for searching for binary millisecond X-ray and radio pulsars. We use numerical simulations to investigate the detectability of pulsars in such systems with P_orb ~ 6 hours, using this technique and three widely used pulsar search methods. These simulations demonstrate that the Partial Coherence Recovery Technique is on average several times more sensitive at detecting pulsars in close binary systems when the data span is more than 2 orbital periods. The systems one may find using such a method can be used to improve the constraints on the coalescence rate of compact objects and they also represent those systems most likely to be detected with gravitational wave detectors such as LISA

The Binary Pulsar PSR 1908+00 in NGC 6760

We present orbital parameters of the 3.6 ms binary pulsar 1908 +00 in the globular cluster NGC 6760. The orbital period is 3.4 hr, and the mass function is 3 x 10^6 M_⊙ , implying a minimum companion mass of 0.018 M_⊙ . The companion is probably degenerate; and if it is hydrogen, it is close to overflowing its Roche lobe. The only other millisecond binary radio pulsar systems with orbital period < 10 hr and mass function below 10-3 M_⊙ are the eclipsing pulsar 1957+20 and 1744-24A, and the very low mass binary 0021-721. These pulsars are ablating their companions and may be the progenitors of isolated millisecond pulsars. PSR 1908+00 shows no evidence for long-duration eclipses as are seen in 1744-24A, but short-duration eclipses as in 1957 + 20 are not excluded

Subaru optical observations of the old pulsar PSR B0950+08

We report the B band optical observations of an old (17.5 Myr) radiopulsar PSR B0950+08 obtained with the Suprime-Cam at the Subaru telescope. We detected a faint object, B=27.07(16). Within our astrometrical accuracy it coincides with the radio position of the pulsar and with the object detected earlier by Pavlov et al. (1996) in UV with the HST/FOC/F130LP. The positional coincidence and spectral properties of the object suggest that it is the optical counterpart of PSR B0950+08. Its flux in the B band is two times higher than one would expect from the suggested earlier Rayleigh-Jeans interpretation of the only available HST observations in the adjacent F130LP band. Based on the B and F130LP photometry of the suggested counterpart and on the available X-ray data we argue in favour of nonthermal origin of the broad-band optical spectrum of PSR B0950+08, as it is observed for the optical emission of the younger, middle-aged pulsars PSR B0656+14 and Geminga. At the same time, the optical efficiency of PSR B0950+08, estimated from its spin-down power and the detected optical flux, is by several orders of magnitude higher than for these pulsars, and comparable with that for the much younger and more energetic Crab pulsar. We cannot exclude the presence of a compact, about 1'', faint pulsar nebula around PSR B0950+08, elongated perpendicular to the vector of its proper motion, unless it is not a projection of a faint extended object on the pulsar position.Comment: 8 pages, LaTeX, aa.cls style, 5 PS figures, submitted to A&A. Image is available in FITS format at http://www.ioffe.rssi.ru/astro/NSG/obs/0950-subar

Predicting the Starquakes in PSR J0537-6910

We report on more than 7 years of monitoring of PSR J0537-6910, the 16 ms pulsar in the Large Magellanic Cloud, using data acquired with the RXTE. During this campaign the pulsar experienced 23 sudden increases in frequency (``glitches'') amounting to a total gain of over six ppm of rotation frequency superposed on its gradual spindown of d(nu)/d(t) = -2e-10 Hz/s. The time interval from one glitch to the next obeys a strong linear correlation to the amplitude of the first glitch, with a mean slope of about 400 days ppm (6.5 days per uHz), such that these intervals can be predicted to within a few days, an accuracy which has never before been seen in any other pulsar. There appears to be an upper limit of ~40 uHz for the size of glitches in_all_ pulsars, with the 1999 April glitch of J0537 as the largest so far. The change in the spindown of J0537 across the glitches, Delta(d(nu)/d(t)), appears to have the same hard lower limit of -1.5e-13 Hz/s, as, again, that observed in all other pulsars. The spindown continues to increase in the long term, d(d(nu)/d(t))/d(t) = -1e-21 Hz/s/s, and thus the timing age of J0537 (-0.5 nu d(nu)/d(t)) continues to decrease at a rate of nearly one year every year, consistent with movement of its magnetic moment away from its rotational axis by one radian every 10,000 years, or about one meter per year. J0537 was likely to have been born as a nearly-aligned rotator spinning at 75-80 Hz, with a |d(nu)/d(t)| considerably smaller than its current value of 2e-10 Hz/s. The pulse profile of J0537 consists of a single pulse which is found to be flat at its peak for at least 0.02 cycles.Comment: 54 pages, 12 figures. Accepted for publication in The Astrophysical Journal. Cleaner figure 2. V4 -- in line with version accepted by Ap

The effect of realistic equations of state and general relativity on the "snowplow" model for pulsar glitches

Many pulsars are observed to "glitch", i.e. show sudden jumps in their rotational frequency $\nu$, some of which can be as large as $\Delta \nu/\nu\approx 10^{-6}-10^{-5}$ in a subset of pulsars known as giant glitchers. Recently Pizzochero (2011) has shown that an analytic model based on realistic values for the pinning forces in the crust and for the angular momentum transfer in the star can describe the average properties of giant glitches, such as the inter-glitch waiting time, the step in frequency and that in frequency derivative. In this paper we extend the model (originally developed in Newtonian gravity and for a polytropic equation of state) to realistic backgrounds obtained by integrating the relativistic equations of stellar structure and using physically motivated equations of state to describe matter in the neutron star. We find that this more detailed treatment still reproduces the main features of giant glitches in the Vela pulsar and allows us to set constraints on the equation of state. In particular we find that stiffer equations of state are favoured and that it is unlikely that the Vela pulsar has a high mass (larger than $M\approx 1.5 M_\odot$).Comment: 15 pages, 8 figures, submitted to MNRA

Towards energetically viable asymmetric deprotonations : selectivity at more elevated temperatures with C2-symmetric magnesium bisamides

A novel chiral magnesium bisamide has enabled the development of effective asymmetric deprotonation protocols at substantially more elevated temperatures. This new, structurally simple, C2-symmetric magnesium complex displays excellent levels of asymmetric efficiency and energy reduction in the synthesis of enantioenriched enol silane

Twenty Years of Galactic Observations in Searching for Bursts of Collapse Neutrinos with the Baksan Underground Scintillation Telescope

The results of twenty-year-long Galactic observations in neutrino radiation are summarized. Except for the recording of a neutrino signal from the supernova SN 1987A, no Galactic bursts of collapse neutrinos have been detected. An upper bound on the mean frequency of gravitational collapses in our Galaxy was obtained, $f_{collapse} (90$.Comment: latex, 7 pages, 2 eps figure

Very-high-energy gamma radiation associated with the unshocked wind of the Crab pulsar

We show that the relativistic wind in the Crab pulsar, which is commonly thought to be invisible in the region upstream of the termination shock at R < 0.1 pc, in fact could be directly observed through its inverse Compton gamm-ray emission. The search for such specific component of radiation in the gamma-ray spectrum of the Crab can provide unique information about the unshocked pulsar wind that is not accessible at other wavelengths.Comment: 11 pages, 11 figures, to appear in one of the April issues of MNRA

The Mass of the Compact Object in the X-Ray Binary Her X-1/HZ Her

We have obtained the first estimates of the masses of the components of the Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the formation of the H_gamma absorption line: mx=1.8Msun and mv=2.5Msun. These mass estimates were made in a Roche model based on the observed radial-velocity curve of the optical star, HZ Her. The masses for the X-ray pulsar and optical star obtained for an LTE model lie are mx=0.85\pm0.15Msun and mv=1.87\pm0.13Msun. These mass estimates for the components of Her X-1/HZ Her derived from the radial-velocity curve should be considered tentative. Further mass estimates from high-precision observations of the orbital variability of the absorption profiles in a non-LTE model for the atmosphere of the optical component should be made.Comment: 20 pages, 4 tables, 8 figure