bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of motoneuron death in the spinal nucleus of the bulbocavernsus
Authors: Forger Nancy G. , Hodges Lynn L. , Roberts Sarah L. , Breedlove S. Marc
Published: May 2005

A sexual dimorphism in the number of motoneurons in the spinal nucleus of the bulbocavernosus (SNB) of rats is engendered by a sex difference in ontogenetic cell death. Testicular secretions, specifically androgenic steroids, reduce SNB motoneuron death in males. The fate of the target muscles generally mirrors that of the motoneurons, and androgens appear to exert their effects upon the target muscles, sparing the motoneurons as a secondary consequence. Treatment with ciliary neurotrophic factor can also spare SNB motoneurons in newborn females, raising the possibility that this factor normally mediates androgen's effect upon motoneuron survival. The ontogeny of calcitonin gene‐related peptide immunoreactivity is delayed in SNB cells compared with other motoneurons and is further delayed in the SNB cells of females. In both sexes, calcitonin gene‐related peptide is detected after the period of SNB motoneuron death is complete. A sex difference in motoneuron number is also seen in the human homologue of the SNB and, because ontogenetic death of motoneurons in humans overlaps the period of androgen secretion, may arise in a manner similar to that in the rat SNB. © 1992 John Wiley & Sons, Inc.
Claw asymmetry in lobsters: Case study in developmental neuroethology
Authors: Govind C. K.
Published: May 2005

An enduring debate in the study of development is the relative contribution of genetic and epigenetic factors in the genesis of an organism, that is, the nature vs. nurture debate. The behavior of the paired claws in the lobster offers promising material for pursuing this debate because of the way they develop. The paired claws and their closer muscles are initially symmetrical; both are slender in appearance and have a mixture of fast and slow fibers in their closer muscles. During a critical period of development, they become determined into a major (crusher) and minor (cutter) claw and during subsequent development acquire their final form and behavior: The crusher becomes a stout, molar‐toothed claw capable of closing only slowly because its closer muscle has 100% slow fibers while the cutter becomes a slender, incisor‐toothed claw capable of closing rapidly because its closer muscle has 90% fast fibers. Our initial hypothesis was that the more active claw became the crusher and its less active counterpart the cutter. Presumably, nerve activity would influence muscle transformation, which in turn would influence the exoskeleton to which they attach and hence claw morphology. Curtailing nerve activity to the claw prevented crusher development, while reflex activation of a claw promoted its development; both results support the notion that nerve activity directly regulates claw form and function. This is not, however, the case, for when both claws were reflexly exercised neither formed a crusher, signifying rather that bilateral differences in predominantly mechanoreceptive input to the paired claws somehow lateralized the claw ganglion [central nervous system (CNS)] into a crusher and cutter side. The side experiencing the greater activity becomes the crusher side while the contralateral side becomes the cutter and is also inhibited from ever becoming a crusher. This initial lateralization in the CNS is expressed, via as yet unknown pathways, at the periphery in claw morphology, muscle composition, and behavior. The critical period defines a time when the CNS is susceptible to being lateralized into a crusher and cutter side. Such lateralization is dependent upon experience of the environment in the form of mechanoreceptive input. In the absence of such experience, the CNS is not lateralized and paired cutter claws develop. Thus, while the critical period for crusher determination is genetically determined the actual trigger is influenced by experience. © 1992 John Wiley & Sons, Inc.
Fundamental motor patterns of the mammalian fetus
Authors: Robinson Scott R. , Smotherman William P.
Published: May 2005

Techniques that permit direct observation of fetuses in vivo recently have expanded our understanding of prenatal behavioral development in mammals. Although fetal motor activity seems to lack the dynamic, goal‐directed character of postnatal behavior, the dimensions that define behavioral organization after birth are applicable to the movements expressed by fetuses. Fetal activity exhibits temporal, sequential, and spatial organization that emerges between the inception of movement and term. Fetal rodents, for example, exhibit coordinated motor patterns antecedent to postnatal righting, locomotion, suckling, maternal–infant communication and grooming behavior, while other action patterns appear to be functional adaptations to the intrauterine niche. Fetuses also are behaviorally responsive to sensory stimulation and changes in environmental conditions in utero. Expression of these behavioral properties emphasizes continuity between prenatal and postnatal life while implying an adaptive role for behavior before birth. © 1992 John Wiley & Sons, Inc.
Activity‐driven sharpening of the retinotectal projection in goldfish: Development under stroboscopic illumination prevents sharpening
Authors: Schmidt John T. , Buzzard Marlene
Published: May 2005

Blocking or synchronizing activity during regeneration of the retinotectal projection prevents both the sharpening of the retinotopic map recorded on tectum and the refinement of the structure of individual arbors within the plane of the map, and this refinement is triggered by N‐methyl‐d‐aspartate (NMDA) receptors. We tested whether activity‐driven refinement also occurs during development of the projection in larval and young adult goldfish. Shortly after hatching, larval goldfish were placed into tanks within light‐tight chambers illuminated by a xenon strobe at 1 Hz for 14 h of each daily cycle. Fish were reared for 1.5–2 years, until large enough to record in our retinotectal mapping apparatus (6 cm length). Age‐ and size‐matched controls had normal maps with multiunit receptive fields (MURFs) recorded at each tectal point of 10.8° (0.16 S.E.M., n = 5), whereas the strobe‐reared fish had only roughly retino‐topic maps with much enlarged MURFs averaging 26.7° (1.41 S.E.M., n = 5). This enlargement represents an abnormal convergence onto each tectal point, as the maps failed to sharpen during development. The arbors of individual retinal axons were stained with horseradish peroxidase (HRP) in larval fish and in adult strobereared and control fish. They were drawn with camera lucida from tectal whole mounts, and analyzed for spatial extent in the plane of the retinotopic map, order of branching, number of branch endings, depth of termination, and caliber of the parent axon. Arbors from larval fish (1–2 weeks) were small (approximately 50 × 40 μm) with less than 10 branches, occupied a single strata, and could not be separated into different classes by caliber of axon. The 87 arbors stained in control adult fish (6 cm long) were much like previously examined adult arbors, with those from fine, medium, and coarse axons averaging 115, 166, and 194 μm in extent, respectively, and having 17–24 branch endings. The 110 arbors from 12 strobe‐reared fish were often abnormal. Although the fasciculation was normal, the extrafascicular routes were abnormal with reversing turns. The axons often had branches along their course, and these branches were scattered across a wider extent, rather than forming a distinct cluster. In contrast, neither the number of branches nor the depths of termination was significantly changed in any group. The coarse caliber arbors were most abnormal, being 64% longer and 30% wider than controls. The fine caliber arbors were also significantly larger by about 20%, but the medium caliber arbors were not enlarged. The enlarged arbors partially account for the unsharpened electrophysiological maps. Together the results show that during development, as well as during regeneration, the retinotectal map is subject to an activity‐driven sharpening process. © 1993 John Wiley & Sons, Inc.
Clusterin levels increase during neuronal development
Authors: O'Bryan M. K. , Cheema S. S. , Bartlett P. F. , Murphy B. F. , Pearse M. J.
Published: May 2005

The expression of clusterin has been shown to be elevated in several models of experimentally induced programmed cell death and in association with a number of neurodegenerative conditions. In order to test whether this protein is expressed in neurons during development, the expression of clusterin was examined in the developing nervous system, using immunohistochemistry and mRNA analysis. Clusterin expression was observed in the earliest neurons of the cortical plate on embryonic day (E) 12. Thereafter, the intensity of clusterin staining continued to increase in an age‐dependent manner, with the greatest intensity of staining being found in the postnatal mature brain. Virtually all neurons were clusterin‐positive and there was no evidence for the appearance of clusterin‐positive cells specifically during epochs of programmed neuronal death in the embryo. This study suggests that clusterin has a role in neuronal maturation and it is unlikely to be associated exclusively with neuronal cell death. © 1993 John Wiley & Sons, Inc.
Identification of molecules in a muscle extracellular matrix extract that promotes process outgrowth from cultured adult frog motoneurons
Authors: Kuffler Damien P. , Luethi Theres
Published: May 2005

The molecular composition of the substrate on which neurons are cultured is critical for their attachment, survival, and extension of processes. The aim of the present experiments was to characterize the molecules in an extracellular matrix (ECM) extract that promotes the outgrowth of processes from cultured adult frog motoneurons. An extract was made of skeletal muscle ECM and tested as a substrate for cultured motoneurons. The average total process length of motoneurons cultured on this crude ECM extract is greater than when the neurons are cultured on concanavalin A, poly‐l‐lysine or mouse tumor (EHS) laminin. Gel filtration of the ECM extract yielded fractions with an increased specific activity for promoting process outgrowth. The most active fractions exhibit a single major polypeptide band of ca. 1 mD and two minor bands of ca. greater than 1 mD and 205 kD upon sodium dodecyl sulfate gel electrophoresis. Under reducing conditions, three major bands were seen of 340, 205, and 200 kD. Electron microscopy of rotary‐shadowed ECM fractions showed macromolecules with a cross‐shaped structure similar to vertebrate and invertebrate laminin, a rod‐like molecule resembling vertebrate and invertebrate collagen type IV, and a third molecule similar in appearance to vertebrate fibrillin. These results represent the first step in analyzing the role of substrate molecules in promoting neuromuscular reinnervation. © 1993 John Wiley & Sons, Inc.
Postsynaptic regulation of the development and long‐term plasticity of Aplysia sensorimotor synapses in cell culture
Authors: Glanzman David L.
Published: May 2005

The monosynaptic component of the neuronal circuit that mediates the withdrawal reflex of Aplysia californica can be reconstituted in dissociated cell culture. Study of these in vitro monosynaptic connections has yielded insights into the basic cellular mechanisms of synaptogenesis and long‐term synaptic plasticity. One such insight has been that the development of the presynaptic sensory neurons is strongly regulated by the postsynaptic motor neuron. Sensory neurons which have been cocultured with a target motor neuron have more elaborate structures—characterized by neurites with more branches and varicosities—than do sensory neurons grown alone in culture or sensory neurons that have been cocultured with an inappropriate target cell. Another way in which the motor neuron regulates the development of sensory neurons is apparent when sensorimotor cocultures with two presynaptic cells are examined. In such cocultures the outgrowth from the different presynaptic cells is obviously segregated on the processes of the postsynaptic cell. By contrast, when two sensory neurons are placed into cell culture without a motor neuron, thier processes readily grow together. In addition to regulating the in vitro development of sensory neurons, the motor neuron also regulates learning‐related changes in the structure of sensory neurons. Application of the endogenous facilitatory trasmitter serotonin (5‐HT) causes long‐term facilitation of in vitro sensorimotor synapses due in part to growth of new presynatpic varicosities. But 5‐HT applied to sensory neurons alone in cultuer does not produce structural changes in these cells. More recently it has been found that sensorimotor synapses in cell culture can exhibit long‐term potentiation (LTP). Like LTP of some hippocampal synapses, LTP of in vitro Aplysia syanpses is regulated by the voltage of the postsynaptic cell. Pairing high‐frequency stimulation of sensory neurons with strong hyperpolarization of the motor neuron blocks the induction of LTP. Moreover, LTP of sensorimotor synapses can be induced in Hebbian fashion by pairing weak presynaptic stimulation with strong postsynaptic depolarization. These findings implicate a Habbian mechanism in classical conditioning in Aplysia. They also indicate that Hebbian LTP is a phylogenetically ancient form of synaptic plasticity. 1994 John Wiley & Sons, Inc.
Retrograde regualtion of presynaptic development during synaptogenesis
Authors: Haydon P. G. , Zoran M. J.
Published: May 2005

Major advances are occurring in our understanding of the events leading to synapse formation. Contact between the growth cone and target tissu leads to intercellular signaling which controls both pre‐ and postsynaptic development of the synapse. The identity of retrograde signals that regualte presynaptic development are beginning to emerge, and the signal transduction cascades that are activated presynaptically are being characterized. Recent studies have shown that both the resting calcium level and activation of presynatptic protein kinase A are critical in the development of the presynaptic terminal. An understanding of these regulatory mechanisms is be ginning to provide insight into the molecular control of synaptic specificity. 1994 John Wiley & Sons, Inc.
Tumor necrosis factor‐α induces substance P in sympathetic ganglia through sequential induction of interleukin‐1 and leukemia inhibitory factor
Authors: Ding Minzhen , Hart Ronald P. , Miller Jonakait G.
Published: May 2005

The present study establishes that tumor necrosis factor‐α (TNF‐α) induction of sympathetic substance P (SP) requires sequential induction of both interleukin (IL‐1) and leukemia inhibitory factor (LIF). TNF‐α dose‐dependently induces SP, an induction that is secondory to an increase in the SP precursor, preprotachykinin (PPT), mRNA. Since TNF‐α conditioned medium (CM) mimics the effect of TNF‐α by raising SP, actions that are not antagonized by a neutralizing TNF‐α antibody, TNF‐α induction of SP is mediated by a soluble intermediate or intermediates. The blockade of TNF‐α action by a specific IL‐1 receptor antagonist and the induction of IL‐1 mRNA by TNF‐α suggest that IL‐1 is one of the intermediates. Moreover, because immunoprecipitation with LIF antibodies decreases SP‐inducing activity of TNF‐α CM, and because LIF mRNA is also induced by TNF‐α, LIF is a second intermediate. Furthermore, TNF‐α‐induced LIF mRNA is blocked by the IL1 receptor antagonist, whereas IL‐1‐induced LIF mRNA is not affected by TNF‐α antibodies, suggesting that TNF‐α first induces IL‐1, and IL‐1 subsequently induces LIF. These data suggest that TNF‐α induces SP in sympathetic ganglia through the sequential inductions of IL1 and LIF. © 1995 John Wiley & Sons, Inc.
Expression of engrailed in an array of identified sensory neurons: Comparison with position, axonal arborization, and synaptic connectivity
Authors: Blagburn Jonathan M. , Gibbon Charles R. , Bacon Jonathan P.
Published: May 2005

engrailed (en) is expressed in the posterior region of embryonic segments and appendages of the cockroach, Periplaneta americana. By 23% of embryogenesis En immunoreactivity is apparent in the dorsal half of the cercus, appendages of segment A11. By 40% of development, En staining is present in the dorsomedial half of the cercus. The nucleus of the medial filiform hair sensory neuron (M), born in this region, expresses en strongly. Staining is never seen in the lateral neuron (L). En is expressed in M as the sensory axons enter the terminal ganglion and begin to form their different arborizations and synaptic connections. This pattern of expression persists through development to the second instar. In mutant animals with supernumerary filiform hair sensilla, En immunoreactivity is only seen in the medial neurons. In second‐instar and adult cerci en expression is also seen in medially located neurons. We compared the levels of En staining in the array of 25 second instar neurons with their position, axonal arbor type, and synaptic connections. Staining intensity corelates with distance from the cercal midline, suggesting that en is regulated by other circumferential positional determinants. The expression of en does not correlate with the formation of an M‐type arbor. Although 10 of 12 sensory neurons that express en form synapses with giant interneuron 5, the correlation is not precise. These results suggest that, if En does form part of a combinatorial system of positional information in the cercus, its actions are modulated by other gene products. © 1995 John Wiley & Sons, Inc.
Influence of peripheral targets on the expression of calcitonin gene‐related peptide immunoreactivity in rat cranial motoneurones
Authors: McWilliam P. N. , Maqbool A. , Batten T. F. C. , Kaye J. C.
Published: May 2005

Calcitonin gene‐related peptide‐like immunoreactivity (CGRP‐ir) is displayed by motoneurons that innervate striated muscle but is absent from preganglionic parasympathetic motoneurons. One hypothesis to explain this is that CGRP gene expression in motoneurons is, in part, dependent on influences from the innervated organ. To test this hypothesis, we cross‐anastomosed the right hypoglossal and cervical vagal nerves of rats so that the vagal motoneurons grew to innervate the musculature of the tongue. Following a recovery period of 17 to 52 weeks, the distribution of CGRP‐ir in the dorsal motor vagal nucleus was determined in both cross‐anastomosed animals and self‐anastomosed control animals. Successful reinnervation of the tongue musculature by vagal motoneurons was demonstrated by showing that electrical stimulation of the central vagus/peripheral hypoglossal nerve produced a twitch of the tongue muscles. Motoneurones of the dorsal motor vagal nucleus, which now innervated the tongue were found to express CGRP‐ir, which was evident from the double labeling of neurons with both horseradish peroxidase and CGRP‐ir. Motoneurones of the dorsal motor vagal nucleus contralateral to the cross‐anastomosis remained CGRP negative. Similarly, motoneurons of the dorsal motor vagal nucleus in control animals where the vagus nerve was self‐anastomosed remained CGRP negative, showing that an induction of CGRP expression is not a result of nerve section itself. We suggest that a signal from the striated muscle transported retrogradely via the motor axon regulates expression of CGRP‐ir in motoneurons. © 1995 John Wiley & Sons, Inc.
Carbon‐13 nuclear magnetic resonance spectra of some mesoionic xanthine analogs
Authors: Mbagwu G. O. , Bass R. G. , Glennon R. A.
Published: May 2005

Natural abundance 13C NMR chemical shifts have been experimentally determined for a series of mesoionic thiazolo[3,2‐a]pyrimidine‐5,7‐diones. The spectral data are compared with those of related mesoionic dihydrothiazolo[3,2‐a]pyrimidine‐5,7‐diones and mesoionic 1,3,4‐thiadiazolo[3,2‐a]pyrimidine‐5,7‐diones. Resonable correlation between the observed 13C NMR chemical shifts and CNDO/2 total charge densities have been obtained for the different carbon atoms of 8‐methylthiazolo[3,2‐a]pyrimidine‐5,7‐dione.
1H and 13C NMR studies on 3‐aryl‐2‐thioxo‐4‐oxazolidinones and 3‐arylrhodanines
Authors: Aksaç Zihni , Pinar Esat , Içli Sîddîk
Published: May 2005

3‐Aryl‐2‐thioxo‐4‐oxazolidinones and 3‐arylrhodanines have been studied for magnetic non‐equivalence of diastereotopically related proton and 13C nuclei in rotational isomers, and for steric interactions between the aryl and heterocyclic moieties of these compounds. For the majority of rotational isomers the barriers to internal rotation about the aryl CN bond were >100 kJ mol−1, due to the steric bulk of the thiocarbonyl group. Chemical isolation of several of the diastereomers was achieved. The enhanced steric effect and the difference in the electronic effect of the sulphur atom in relation to the oxygen atom appeared to have no influence on the small chemical shift differences of the rotational isomers, detected for some 1H and some 13C nuclei.
Hydroxy group substituent effects on 1H NMR chemical shifts in the structural elucidation of spirostanes
Authors: Jaffer Jaffer A. , Crabb Trevor A. , Turner Christopher H. , Blunden Gerald
Published: May 2005

1H NMR chemical shifts in spirostanes have been determined by spin‐decoupling difference spectroscopy. Substituent effects of 7β‐OH on 15‐methylene proton shifts, 1β‐OH on 11α‐ and 2α‐proton shifts and 6α‐OH on 4α‐proton shifts have been determined and used in the structural assignment of spirostanes.
Mass spectrometry and organic analysis—XII αβ‐Unsaturated secondary alcohols
Authors: Willhalm B. , Thomas A. F.
Published: May 2005

The fact that some αβ‐unsaturated alcohols give mass spectra that bear some similarity with the corresponding saturated ketones is discussed, and the double hydrogen transfer necessary to accommodate this is examined by deuterium labelling.
Mass spectrometry in structural and stereochemical problems—CLXIV. Electron impact promoted fragmentation of some thiosemicarbazones
Authors: Sheikh Younus M. , Duffield A. M. , Djerassi Carl
Published: May 2005

The mass spectral fragmentation of thiosemicarbazone derivatives of some typical aliphatic, alicyclic and aromatic aldehydes and ketones has been rationalized using high resolution mass spectrometry supplemented by deuterium labeling. Thiosemicarbazone derivatives of carbonyl compounds yield mass spectra which have little in common with those generated by their semicarbazone analogs.
On the mass spectra of some alkyl digermanium compounds
Authors: De Ridder J. J. , Dijikstra G.
Published: May 2005

This paper reports the monoisotopic mass spectra of the compounds (CH3)GeGe(CH3)3,(C2H5)3GeGe(C2H5)3 and (CH3)3GeGe(C2H5)3. With the aid of metastable ion transitons and appearance potentials the fragmentation patterns can be given.

The dominant reactions are explained in terms of the valence of the metal atom. According to the valence rule the possibility of forming an ion in which two germanium atoms are bonded to five other groups (alkyl or hydrogen) determines greatly the spectra, while successive elimination of the methyl groups appears to be difficult and elimination of the ethyl groups is a predominant process.
Stereoisomeric effects on mass spectra—I. A Review
Authors: Meyerson Seymour , Weitkamp A. W.
Published: May 2005

The unimolecular reactions that give rise to mass spectra are controlled by spatial relationships and energy considerations. In molecules that contain a heteroatom, elimination reactions, involving bond‐making as well as breaking, are often prominent, e.g. loss of water from alcohols. The ease of such reactions depends on spatial relationships in the molecule, and the resultant ion intensities in the spectra of geometric isomers can consequently be correlated with differences in geometry and hence furnish a basis for assigning structures. Processes that do not involve bond‐making do not have such rigorous geometric requirements, but depend rather on attainment of a transition state defined in terms of a minimum energy content. Common product ions from stereoisomeric hydrocarbons seem often to arise via a common transition state. When this condition holds, the difference between the enthalpies of the isomers is reflected in the relative appearance potentials and–though the cause‐and‐effect relationship here is less direct and more readily obscured by other factors–relative intensities of the common product derived from the isomers. In both classes of processes, the spectra of stereoisomers can be simplified and made more distinctive by lowering source temperature and ionizing voltage.
Electron impact‐induced rearrangement of trimethylsilyl groups in long chain compounds
Authors: Draffan G. H. , Stillwell R. N. , McCloskey James A.
Published: May 2005

Mass spectra of trimethylsilyl (TMS) derivatives of long chain dicarboxylic acids, hydroxy acids, cyano acids, and terminal diols, dithiols and diamines have been examined. A number of fragmentation pathways involving rearrangement of partial or intact TMS groups between the termini or remote points in the chain have been determined, using deuterium and carbon‐13 labeling, and high resolution mass spectrometry. Knowledge of the occurrence of functional group migrations of this type is essential to the correct interpretation of mass spectra of TMS derivatives, which are now in wide use in mass spectrometry and gas chromatography. These data in addition provide further evidence for the general ability of remote functional groups to interact, by winding or coiling of long chains. A number of interesting doubly‐charged ions are reported, in which the charges are reported, in which the charges are located at opposite ends of long chains, and for which no singly‐charged counterparts are observed.
Electron‐impact studies of organometallic molecules—VII. Some transition metal complexes derived from 3,3,3‐trifluoroprop‐1‐yne
Authors: Bruce M. I.
Published: May 2005

The mass spectra of ten complexes derived from 3,3,3‐trifluoroprop‐1‐yne, namely (CF3CCH)CO2(CO)6, (CF3CCH) [πC5H5Ni]2, (CF3CCH)3Co2(CO)4, CF3CH2C[Co(CO)3]3,

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are discussed in terms of their structures. The major processes observed can be satisfactorily explained in terms of (i) loss of carbonyl groups, if present; (ii) loss of one fluorine atom from the parention (iii) elimination of neutral metal fluorides, with ligand transfer reactions in the case of the iron complexes; (iv) elimination of neutral fluorocarbon molecules.
Zur Massenspektrometrie von Nitrophenylverbindungen—I. Nitrophenylphydrazone Aromatischer Aldehyde und Ketone und Verweandte Verbindungen
Authors: Seibl J. , Völlmin J.
Published: May 2005

Die Fragmentierung von Nitrophenylhydrazonen aromatischer Aldehyde und Ketone, von Nitrostillbenen, Nitrobenzalacetophenonen und analogen Verbindungen unter Elektronenbeschuss wird entscheidend durch intramolekulare Oxidationsreaktionen beeinflusst, sofern sich eine Nitrogruppe in o‐Stellung zum ungesättigten substituenten befindet. Es findet eine Sauerstoffübertragung von der o‐Nitrogruppe auf die Hydrazon‐ oder Stilbendoppelbindung statt; ein wesentlicher Teil der charakterisierenden Fragmente in den Massenspektren dieser Verbindungen stammt aus dem Zerfall dieser Sauerstoffübertragungsprodukte. 20 Spektren von 40 untersuchten Verbindungen werden präsentiert und diskutiert. Eine Reihe weiterer umlagerungsreaktionen werden beobahtet. Eine konjugierte zusätzliche Dopplbindung in der Hydrazonkette ändert die Reaktivität der Verbindung vollsändig. auch die Fragmentierung gesättigter Substituenten (Cyclopropyl) kann durch eine o‐Nitrogruppe entscheidend beeinflusst werden.
Elektronenstoss‐Induzierte Molekülumlagerungen—I. Massenspektrometrische Fragmentierungen von Azinen und Phosphazinen
Authors: Zeeh Bernd , Beutler Rolf
Published: May 2005

Die Massenspektren von 15 Azinen sowie 5 Phosphazinen werden mittels deuterium‐Markierung und exakten Massenmessungen untersucht. Azine von Aldehyden eliminieren HCN und (HCN + H) aus dem Molekülion, was mit einer Umlagerung verbunden ist. Azine von Ketonen spalten zuerst ein Aryl‐bzw. Akylradikal ab und lagern sich anschliessend um unter eliminieung von CN. oder (CN. + H). Analogien zur photolytischen oder termischen Abspaltungvon Stickstoff aus Azinen wurden nicht gefunden. o, o′‐Dinitro‐benzaldazin erleidet unter Elektronenstoss eine doppelte Sauerstoffumlagerung, bei de CO2 eliminiert wird. Phosphazine zeigen bei Elektronenbeschuss ein ähnliches Verhalten wie bei der Thermolyse.
Chemistry of lichen constituents—VII: Mass spectra of some pulvic acid derivatives
Authors: Letcher R. M.
Published: May 2005

The mass spectra of three methoxypulvic dilactones, four methyl esters of methoxypulvic acids and five methyl ethers of pulvic acid derivatives have been measured and rationalised employing accurate mass measurements and metastable peak assignments to substantiate the proposed fragmentations and rearrangements. In particular, the mass spectral differences and similarities between the isomeric methoxypulvic dilactones, between their methanolysis products and between the isomeric methyl ethers, are rationalised.
Mass spectrometric studies on o‐terphenyl‐2‐13C: Identification of compounds related to its synthesis and fragmentation processes
Authors: Copet A. , Facchetti S.
Published: May 2005

After identification of the impurities, separated from synthesized orthoterphenyl (I) labelled in position 2 with 13C, i.e. o‐xenylcyclohexanol (II), o‐xenylcyclohexene (III), hexahydrotriphenylene (IV) and o‐xenylcyclohexane (V), the fragmentation processes under electron‐impact of molecules I, II and IV have been studied, advantage being taken of their 13C labelling.

Mass spectrometric studies were carried out on an AEI MS‐9 for determination of the atomic composition of the main ions and on a MAT CH‐4 instrument for quantitative determination of 12C and 13C species, at low energy, assuming an equal sensitivity.

The 13C labelling of position 2 in I, has not yet given clear evidence of a formerly assumed rearrangement into phenanthrenic structure after ring opening.

The fragmentation of molecule II occurs in two ways, i.e. into a series of hydrocarbon fragments, produced from the molecular ion by loss of H2O or into fragments still containing the oxygen atom. The difference between the fragmentation processes of the two series depends on the fact that the loss of H2O from the molecule stabilizes the two carbon atoms adjacent to the C carrying the hydroxyl group. This is shown by the relatively higher 13C content of the hydrocarbon fragment in C15 compared with that of the equivalent oxygenated fragment.

The labelling in IV shows how the rupture of the saturated ring occurs under electron‐impact, the first C removed being the one nearest to the central ring.
Zum Verhalten von Trimethylalkoxysilanen bei Elektronenstoss
Authors: Dube G. , Kriegsmann H.
Published: May 2005

Es werden die Massenspektren von Trimethylaklkoxysilanen dr Typen (CH3)3SiO(CH2)nCH3 (n = 0‐8) und (CH3)3SiO(CH2)nCH(CH3)2 (n = 0‐3) wiedergegeben und die meisten Abbaureaktionen der Verbindungen bei Elektronenstoß durch metastabile Ionen belegt. Die von Diekman, Thomoson und Djerassi für Trimethypentoxysilane angegebenen Zerallsmechanisman laufen auch bei den untersuchten Substanzen ab. Es werden Besonderheiten beim Ablauf dieser Reaktionen bei Trimethylalkoxsilanen mit längerer und kürzerer Alkoxykette diskutiert und einige weitere Zerfallsreaktionen mitgeteilt.
The question of hydrogen and randomization in phenyl isocyanide
Authors: Yeo Adrian N. H. , Cooks R. Graham , Williams Dudley H.
Published: May 2005

The loss of HCN and DCN from 2,4,6‐d3‐phenyl isocyanide is preceded by H/D randomization in the large majority of k‐states which could be sampled in this study.
Electron‐impact studies—XVIII. Fragmentation of some epimeric 7‐substituted norbornenes
Authors: Das K. G. , Nayar M. S. B. , Chinchwadkar C. A.
Published: May 2005

The fragmentation modes of some epimeric 7‐substituted norbornenes have been established from deuteration and high resolution studies. Stereochemical differences were found to have very little influence in directing the fragmentation modes of these epimers. Formation of common intermediates or transition states by ring opening process has been proposed to rationalise the mass spectral behaviour of these compounds.
An assignment of approximate internal energy distributions through substituent effects to ions produced by electron‐impact
Authors: Buck Richard P. , Bursey Maurice M.
Published: May 2005

A probability distribution of internal energies is derived for aromatic molecular ions which can decompose to give only a single product whose relative intensity and appearance potential are each a function of Hammett sigma constants, with certain simplifying assumptions.
Hydrogen randomization in phenyl azide
Authors: Kingston David G. I. , Henion J. D.
Published: May 2005

The loss of both HCN and C2H2 from the phenyl nitrenium cation radical generated from 2,4,6‐d3‐phenyl azide is preceded by H/D randomization.
Bridgehead nitrogen heterocycles—II: The mass spectra of some pyrazolo[1,5‐a]pyridines
Authors: Potts K. T. , Singh U. P.
Published: May 2005

Pyrazolo[1,5‐a]pyridine undergoes fragmentation upon electron‐impact by loss of HCN or C2H2N·. In the 2,3‐dimethyl derivative loss of HCN and CH3CN were both observed from the [M – 1]+ ion and, in the 3‐methyl‐2‐phenyl derivative, loss of PhCN occurred from the corresponding [M – 1]+ ion. Loss of methyl and phenyl radicals was also observed. In 3‐acetyl‐2‐methyl and 3‐benzoyl‐2‐phenyl derivatives, characteristic losses of the CH3CO· and PhCO· groups were noted. The introduction of a 7‐methyl substituent into the six‐membered ring had little effect on the fragmentation pattern.
Mass spectrometry in structural and stereochemical problems—CLXXXIV: Charge localization in fragment ions of amino ketones and esters
Authors: Cable J. , Adelstein G. W. , Gore J. , Djerassi Carl
Published: May 2005

The mass spectral fragmentation of a number of specially synthesized amino esters and ketones has been studied in which the distance between the two functionalities has been varied. The principal fragments formed following initial ionization are the even‐electron immonium ions a and b. Further fragmentation of ion a in the amino esters occurs via non‐specific processes. Therefore it is difficult to establish the degree of mobility of the positive charge in the fragment ions, notably whether the species with the charge present on the oxygen atom makes a significant contribution to the fragmentation. The β‐(IIb) and γ‐(IV) amino ketones show no McLafferty rearrangements after α‐fission, thus demonstrating that uncoupling of the carbonyl π electrons is not a feasible trigger in lieu of charge localization.
The ion kinetic energy spectra of some aromatic hydrocarbons
Authors: Beynon J. H. , Caprioli R. M. , Baitinger W. E. , Amy J. W.
Published: May 2005

The technique of ion kinetic energy spectroscopy has been applied to the study of the aromatic hydrocarbons benzene, toluene, naphthalene, 2‐methyl naphthalene, biphenyl and anthracene. The method is illustrated by a complete study of naphthalene in which transitions of metastable doubly‐ and singly‐charged ions are listed, including reactions in which singly‐charged ions are formed by collision induced charge‐exchange reactions of doubly‐charged ions and by the double process of charge‐exchange and metastable decomposition with loss of one or two hydrogen atoms. Decompositions of doubly‐charged ions into two singly‐charged ions, together with the kinetic energies released in these decompositions, are also given for all the compounds studied.
Metastable ions of methane and their use in calibrating a low mass scale
Authors: Beynon J. H. , Caprioli R. M. , Baitinger W. E. , Amy J. W.
Published: May 2005

The decomposition of metastable positive ions of methane formed by electron bombardment is discussed. Some new collision‐induced decompositions involving the formation of H+, H2+˙ and H3+ have been found in the ion kinetic energy spectrum as well as in the mass spectrum of methane. In the latter case, the ‘metastable peaks’ occur below mass 1 on the mass scale and can be used for mass calibration in this region of the mass spectrum.
Mass spectra of maleimides, isomaleimides, bis‐maleimides, bis‐isomaleimides and the intramolecular photocyclization products of bis‐maleimides
Authors: Feast W. J. , Put J. , De Schryver F. C. , Compernolle F. C.
Published: May 2005

The mass spectral fragmentation of some maleimides, isomaleimides, bis‐maleimides, bis‐isomaleimides and diazatetracyclotetraones (intramolecular photocyclization products of bis‐maleimides) have been investigated. The elimination of carbon dioxide from the molecular ions of these compounds is not generally an important process. Fragment ions arising from the transfer of one or more hydrogen atoms from the eliminated to the charge retaining moiety (and vice versa) are prevalent and the variation in fragment ion intensity with changes in structure is consistent with the mechanisms of the analogous fragmentations of succinimides established by Djerassi's group. The apparently unusual fragmentations of the diazatetracyclotetraones may be rationalized on the basis that the molecular ion consists of three or more different species.
Mass spectra of β‐quinuclidones and β‐benzquinuclidones
Authors: Ermakov A. I. , Sheinker Yu. N. , Mikhlina E. E. , Mastafanova L. I. , Ya. Vorobjova V. , Yanina A. D. , Yakhontov L. N. , Kostyanovsky R. G.
Published: May 2005

The mass spectra of quinuclidone‐3, benzquinuclidone‐3, 2‐azaquinuclidone‐3, 2‐azabenzquinuclidone‐3 and some of their functional substituted derivatives have been investigated. Fragmentation of the compounds investigated has been shown to proceed through the open form of the molecular ion with cleavage of a bridgehead bond containing the carbonyl group and subsequent elimination of carbon monoxide.
Strukturspezifischer Massenspektrometrischer Abbau von mono‐ und di‐n‐alkyl‐substituierten Acetylenverbindungen
Authors: Luftmann H. , Spiteller G.
Published: May 2005

Massenspektren mono‐n‐alkyl‐substituierter Acetylene vom Typ 1, die zumindest 7 Kohlenstoffatome in gerader Kette des Restes R enthalten, sind durch Schlüsselbruchstücke der Masse 82 und 96 gekennzeichnet. Sie zerfallen weiter unter Verlust eines Methylradikals. In den Spektren di‐n‐alkyl‐substituierter Acetylene sind diese Schliiüsselbruchstücke urn eine entsprechende Zahl von Masseneinheiten verschoben. Sie werden unter Eliminierung von C5H10 Teilchen weiter abgebaut. Daneben entstehen auch aus di‐n‐alkyl‐substituierten Acetylenverbindungen Schlüsselbruchstücke der Masse 67, 81, 82 und 95,96.
Preference factors and isotope effects in the loss of H. (D.) and HCN (DCN) from deuterated pyrazoles upon electron‐impact
Authors: Van Thuijl J. , Klebe K. J. , Van Houte J. J.
Published: May 2005

The mass spectra of deuterated pyrazoles show that loss of H. and of HCN from the molecular ion occurs with a very high specificity from the 3(5)‐position. For the two processes isotope effects and preference factors have been determined. Metastable ion decompositions involving the loss of HCN from the [M ‐ H] ‐fragment indicate that the identity of the hydrogen atoms in this fragment is lost to a large extent.
Electron impact studies—LXV: Negative‐ion mass spectrometry of functional groups 2‐aryl‐1,3‐dithianes
Authors: Bowie J. H. , White P. Y.
Published: May 2005

The negative‐ion mass spectra of 2‐aryl‐1,3‐dithianes contain pronounced molecular anions together with fragment ions which are produced by both simple and complex cleavage reactions. These spectra contain further examples of specific hydrogen scrambling processes in negative ions. Nitroaryldithianes give intense negative‐ion spectra, and that of the o‐nitro derivative exhibits an unusual proximity effect. The fragmentation patterns have been examined using both 2H and 13C labelling and the metastable defocusing technique.
Mass spectrometric studies of 4‐oxo‐4,5,6,7‐tetrahydrobenzofurans
Authors: Cortés E. , Salmón M.
Published: May 2005

The mass spectra of alkyl and aryl 4‐oxo‐4,5,6,7‐tetrahydrobenzofurans have been determined and the fragmentation patterns are established unambiguously by deuterium labelling in the 5,5,7,7‐d4 position.
Mass spectra of N and O methyl and methylthiomethyl derivatives of benzophenone oxime
Authors: Leyshon W. M. , Wilson D. A.
Published: May 2005

The mass spectra of benzophenone oxime O‐methyl and O‐methylthiomethyl ethers, α,α‐diphenyl‐N‐methyl and methylthiomethyl nitrones, and some deuterated analogues, are reported. Fragmentation pathways are discussed, with particular reference to the structures of ion m/e 211 found in all the spectra. Some evidence suggests nitrone → O‐ether rearrangement at either neutral molecule or molecular ion level.
Fragmentation de Triazoles Sous L'Impact Electronique—II 1,2,3‐Triazole
Authors: Maquestiau A. , Van Haverbeke Y. , Flammang R. , Elguero J.
Published: May 2005

La similitude de comportement des 1,2,4‐ et 1,2,3‐triazoles sous l'impact électronique est attribuée à la formation de structures ioniques communes. L'étude des transitions métastables correspondant à al perte d'une molécule d'azote semble indiquer que, dans le cas du 1,2,3‐triazole, les deux formes tautoméres coexistent à l'état gzaeux et qu'une isomérisation partielle de l'ion moléculaire se produit dégradation.
Mass spectra of some derivatives of O‐toluenesulphonic acid
Authors: Kubelka V. , Mostecký J.
Published: May 2005

The mass spectra of the derivatives of o‐toluenesulphonic acid show a significant interaction of methyl and SO2R groups. The change of a substituent mainly influences the decomposition mechanism of molecular ions and some fragment ions which are formed from them.1
The study and characterization of nucleosides by mass spectrometry—II: Comparisons between the mass spectra of 3′,5′‐substituted, isomeric pairs of 2,2′‐anhydrouridines
Authors: Westmore J. B. , Lin D. C. K. , Ogilvie K. K.
Published: May 2005

The mass spectra of 2,2′‐anhydrouridines substituted in the 3′ and 5′ positions were studied. When the substituents were acetyl, pivaloyl, trifluoroacetyl or trimethylsilyl, it was found that specific fragmentations occured which could identify the position of the substituent. The specific fragmentations often resolve earlier ambiguities in the interpretation of mass spectra of 2,2′‐anhydropyrimidine derivatives. Mono‐acetyl and mono‐pivaloyl 2,2′‐anhydrouridines are not easily distinguished because of thermal reactions in the sample probe. They may be readily distinguished, however, by acetylation (with acetic anhydride‐d6 for the mono‐acetyl isomers), trifluoroacetylation or trimethylsilylation, followed by mass spectral analysis of the reaction product.
Mass spectrometry in structural and stereochemical problems—CCXXIII:ortho interactions of nitro groups
Authors: Tomer Kenneth B. , Gebreyesus Tarekegn , Djerassi Carl
Published: May 2005

The mass spectra of C13 labeled o‐ nitrobenzoic acid and o‐nitrobenzaldehyde were studied. Earlier proposed fragmentations involving group migration to a charge‐carrying vacant ortho position were verified. A completely unexpected interaction in o‐ nitroanisole was uncovered by O18labeling.
Gas phase studies of N‐nitrosamines by ion cyclotron resonance spectroscopy
Authors: Billets Stephen , Jaffe H. H. , Kaplan Fred
Published: May 2005

The gas phase basicities of a series of cyclic and acyclic N‐nitrosamines were determined by ion cyclotron resonance techniques. The fragmentation pattern and ion‐molecule reactions of these compounds are discussed in terms of high resolution mass spectrometry and deuterium labeling. The presence of a unique rearrangement of the molecular ion is discussed in terms of specific ion‐molecule proton transfer reactions and fragment ion products.
Chemical ionization mass spectrometry studies—VII: Deuterium labeled decanes
Authors: Hunt D. F. , McEwen C. N.
Published: May 2005

CI mass spectra of the five isomeric vicinal d2‐decanes have been recorded using methane and d4‐methane as reagent gases. In contrast to earlier suggestions, we find that a large fraction of the alkyl fragment ions from n‐decane are formed by elimination of olefins from the abundant [M – 1] ion. Only the C9 and C8 fragment ions are produced completely by a one‐step reaction between the decanes and the methane reagent ions. Isotope exchange does not occur between the hydrocarbon and the reagent ions derived from d4‐methane but extensive scrambling of the deuterium label in the d2‐decanes does take place in the [M – 1] ion.
Internal energy effects on the mass spectral fragmentations of some phosphorus heterocycles
Authors: Weringa W. D. , Granoth I.
Published: May 2005

In addition to the elimination of C6H5· and C7H7·, 2,8‐dimethyl‐10‐phenyl‐ and 10‐(p‐tolyl)‐phenothiaphosphines lost C6H5S· and C7H7S·, respectively from high internal energy molecular ions, while the low internal energy ions eliminated C6H5PH and C7H7PH, respectively. 2,8‐Dimethyl‐10‐phenylphenoxaphosphine lost C6H5·, C6H5P and C6H5PH· both in the source and in the first field‐free region, but the expulsion of C6H5O· was not observed.
Etude de la Fragmentation des bis Alkylthio‐3,5 Isothiazoles en Spectrometrie de Masse
Authors: Julien Jacques , Vincent Emile‐Jean , Poite Jean‐Claude , Roggero Jean
Published: May 2005

L'étude du schéma de rupture de 26 bis alkylthio‐3,5 isothiazoles permet de mettre en évidence des modes de rupture assezy pen connus dans la série des isothiazoles. On reconnaît dans le cas des bialkyl thio‐3,5 isothiazoles deux modes importants correspondant respectivement à la perte du radical mercapto et à la perte de deux atomes de soufre. Nous démontros à l'aide des spectres des dérivés deutériés dans chaque position et du dérivé perdeutérié correspondant, le rôle spécifique des substituants alkylthio dans le mécanisme de fragmentration correspondant ` la perte des radicaux alkyle, thioalkyle et mercapto. Un mécanisme de transposition de l'ion moléculaire est envisagé pour expliquer la présence de deux schémas compétitifs de rupture.
Massenspektrometrische Fragmentierungen β‐Substituierter Adamantanone und Adamantandione
Authors: Eckhardt G. , Fehlhaber H.‐W.
Published: May 2005

Durch hoch‐und niederauflösende Massenspektrometrie und durch Bestimmung emtastabiler Ionen mittels Defokussierung wurde die elektronenstoß‐induzierte Fragmentierung einer Reihe β‐substituierter Adamantanone und Adamantandione untersucht. Während die isomeren Brom‐, Jod‐ und Thiocyanato‐adamantanone fast identische Spektren liefern, ist das Fragmentierungsverhalten der Fluor‐ und Chlor‐Verbindungen davon abhängig, ob die Substituenten in Bezug auf den die Carbonyl‐Gruppe enthaltenden Ring axial oder äquatorial angeordnet sind. Hydroxyund Acetoxy‐adamantanone liefern ziemlich komplexe Massenspektren. Adamantandione, die in β‐Stellung durch verschiedene COR‐bzw. NR1R2‐Gruppen substituiert sind, geben charakteristischen Peaks von Ionen, die durch McLafferty‐Umlagerung bzw. α‐Spaltung und anschließende Eliminierung von Kohlenmonoxid und Allyl‐Spaltung gebildet werden Das Fragmentierungsverhalten der isomeren Hydroxycarbomethoxy‐adamantanone und Dihydroxy‐carbomethoxyadamantane wird durch die Orientierung der funktionellen Gruppen bestimmt.
On the correlation between emitter heating current and emitter temperature in field desorption mass spectrometry
Authors: Kümmler D. , Schulten H.‐R.
Published: May 2005

Calibration curves have been established that give an estimate of the temperature in the emission region of high temperature activated field desorption emitters. Two characteristic types of field anodes have been investigated: (1) emitter wires carrying microneedles of 25 to 30 μm length, preferentially used for field desorption of organic compounds; (2) emitters with microneedles of 50 to 60 μm length, which are used for the investigations of polymers by pyrolysis field desorption mass spectrometry.