A. G. Loudon

Identification of the N-terminal blocking groups of trout hemoglobins by mass spectrometry

Low resolution mass spectrometry is now established as a technique for peptide sequence analysis [1 ] . in addition, the method is uniquely useful for sequence analysis ofpeptides with blocked N-terminal residues [2~-~]. We describe here the sequence anMy~is o f the pentapeptides from the N-termini o f the a-chains of Hb trout [ and Hb trout IV. In view of the well established role of the aminote~nini of the a~hains in the Bohr effect and in COs transport in human HbA [5] , f.Ns structural inforr ation on the Hb components from trout represents a step foreward in understanding their structure-function relationship [6].

Identification by mass spectrometry of Nε-formyl-lysine residues in a peptide from bee venom

A mixture of variant forms of the peptide (1) has been isolated from bee venom. The variants have the same amino-acid sequence and arrangement of disulphide bridges as the parent peptide but differ from it in that the side chains of lysine residues at positions 2, 17, and possibly 21 are chemically modified. The modifying group has been identified, by mass spectrometry, as formyl. Each variant probably contains only one modified lysine residue.

Fragmentation of organic molecules under electron impact. Part 1. Ureas

The spectra of all the methylated ureas, ethylene urea, and certain alkyl, alkylaryl, and aryl ureas are reported and discussed. The spectra are all relatively simple, and in the main can be described in terms of bond fission to form R1R2N+ or R3R4[graphic omitted]CO or 1–3 hydrogen rearrangement to form [R1R2NH][graphic omitted] or [R3NCO][graphic omitted]. There is no evidence for the corresponding alkyl or aryl rearrangement.

Electron impact spectroscopy of some simple nitriles

The electronic absorption spectra of acetonitrile, propionitrile and butyronitrile have been determined using the method of electron impact spectroscopy. Spectra are presented which were obtained at 70 eV impact energy and zero scattering angle. Results obtained at 90° scattering angle at lower impact energies are briefly mentioned. The spectra are interpreted in terms of excitations to valence excited states and Rydberg states. Three Rydberg series each are found for acetonitrile and propionitrile. A previously unreported absorption occurring at about 6 eV in each of the zero scattering angle spectra is tentatively assigned as a triplet excitation and one at about 8 eV in the 90° scattering angle spectra is assigned as a triplet excitation.

The mass spectra of meliacins and related compounds. Part I. Gedunin and related compounds

The mass spectra of gedunin and related compounds are reported and the modes of fragmentation discussed. These results should make possible the identification of related compounds by mass spectrometry.

Heavy atom kinetic isotope effects. Part 3.—The chlorine kinetic isotope effect in the gas-phase unimolecular decomposition of ethyl chloride

A study of 35k/37k for the gas-phase elimination of hydrogen chloride from ethyl chloride is reported. The value found at 723 K is 1.001 5 ± 0.000 2. Heavy atom kinetic isotope theory is applied in an attempt to characterise the transition state. It is concluded that there is only a moderate lengthening of the carbon-chlorine bond, and only a little motion of the chlorine atom in the transition state.

Kinetics and mechanisms of the decompositions of the molecular ions of pentanal and its monomethyl-substituted homologues in the picosecond to microsecond time interval following field ionization

The kinetics of decomposition of pentanal and its monomethyl homologues, including hexanal, have been studied as a function of time following field ionisation (FI). With the aid of these results and other energetic measurements, the McLafferty rearrangement in the case of hexanal is shown to occur by a stepwise mechanism.

Low energy electron impact spectra of some simple alkynes

A low energy electron impact spectrometer is described and the spectra of ethyne, propyne, but-1-yne and but-2-yne presented. The spectra are explained in terms of transitions to valence excited states and Rydberg series. One of the Rydberg series for but-1-yne is revised, and a Rydberg series is proposed for but-2-yne.

Comparison between unimolecular gas phase pyrolysis and electron impact fragmentation. Part II. The gas phase pyrolysis of tetralin and some related hetereocycles

The thermal fragmentation of tetralin, chroman, isochroman, thiochroman, isothiochroman, 1,2,3,4-tetrahydroquinoline and 1,2,3,4-tetrahydroisoquinoline has been investigated and compared with the fragmentation under electron impact reported in the preceding paper. Many similarities as well as some differences are noted. As a result of this work a new synthesis of the o-quinodimethane-benzocyclobutene system has been developed and the reactions of the former isomer with unreactive dienophiles are reported.

Alkaloids from croton species. Part VI. Mass spectrometric studies of the crotonosine alkaloids

The mass spectra of crotonosine and some related compounds are reported and the composition of the major fragments determined by high-resolution mass measurements. Modes of fragmentation are discussed. In addition the mass spectra of the model compound tetrahydroisoquinoline and its N-methyl and N-acetyl derivatives are reported and discussed.