bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sexual differentiation and hormonal regulation of the laryngeal synapse in Xenopus laevis
Authors: Tobias Martha L. , Kelley Darcy B. 
Published: May 2005

AbstractIn Xenopus laevis frogs, sex differences in adult laryngeal synapses contribute to sex differences in vocal behavior. This study explores the development of sex differences in types of neuromuscular synapses and the development and hormone regulation of sex differences in transmitter release. Synapses in the juvenile larynx have characteristics not found in adults: juvenile muscle fibers can produce subthreshold or suprathreshold potentials in response to the same strength of nerve stimulation and can also produce multiple spikes to a single nerve stimulus. Juvenile laryngeal muscle also contains the same synapse types (I, II, and III) as are found in adult laryngeal muscle. The distribution of laryngeal synapse types in juveniles is less sexually dimorphic than the distribution in adults. Analysis of quantal content indicates that laryngeal synapses characteristically release low amounts of transmitter prior to sexual differentiation. Quantal content values from male and female juveniles are similar to values for adult males and are lower than values for adult females. When juveniles are gonadectomized and treated with exogenous estrogen, quantal content values increase significantly, suggesting that this hormone may increase transmitter release at laryngeal synapses during development. Gonadectomy alone does not affect quantal content of laryngeal synapses in either sex. Androgen treatment decreases quantal content in juvenile females but not males; the effect is opposite to and smaller than that of estrogen. Thus, muscle fiber responses to nerve stimulation and transmitter release are not sexually dimorphic in juvenile larynges. Transmitter release is strengthened, or feminized, by the administration of estradiol, an ovarian steroid hormone. © 1995 John Wiley & Sons, Inc.
A general survey of the proton spin–lattice relaxation rates of steroids
Authors: Colebrook Lawrence D. , Hall Laurance D. 
Published: May 2005

AbstractThe spin‐lattice relaxation rates of the aromatic, alkene, hydroxyl, methine and methyl protons of 19 steroid derivatives have been measured using the null point method. A simple procedure is described whereby the R1 values of molecules which have different motional tumbling rates can be directly inter‐compared, and it is shown that such ‘normalized’ relaxation data can provide novel insight concerning both the geometry and the local molecular motion of these substances in solution.
1H NMR parameters of the N‐terminal 13‐residue C‐peptide of ribonuclease in aqueous solution
Authors: Rico M. , Nieto J. L. , Santoro J. , Bermejo F. J. , Herranz J. 
Published: May 2005

AbstractThe 1H NMR chemical shifts and the spin‐spin coupling constants of the non‐exchangeable protons of the N‐terminal 13‐residue C‐peptide of ribonuclease A, obtained by cleavage of the enzyme with cyanogen bromide, have been measured in a 5 mM solution in D2O (pH 3.0, 24°C) at 360 MHz. The titration parameters for end groups (Lys‐1 and homo‐Ser‐13) and side chains (Lys‐1, Glu‐2, Lys‐7, Glu‐9 and His‐12) have been determined. The chemical shifts, their temperature coefficients and the vicinal coupling constants, 3J(HNCH‐α), for the exchangeable NH protons have been measured in a 5 mM solution in D2O/H2O (1:9 v/v) at pH 3.0. An assignment of observed signals to individual residue protons based on characteristic shifts, standard double resonance experiments, spectral simulations and titration shifts is proposed. All experimental evidence indicates that under the conditions studied the C‐peptide is in a random coil form.
1H dynamic nuclear magnetic resonance study of hindered rotations in N‐aryl‐N‐benzyl alkyl carbamates
Authors: Julià S. , Ginebreda A. , Sala P. , Sancho M. , Annunziata R. , Cozzi F. 
Published: May 2005

AbstractThe NMR variable temperature behaviour of a series of N‐aryl‐N‐benzyl alkyl carbamates was investigated. The barrier to rotation about the N‐aryl bond was determined for all the compounds studied. The values obtained, which are in good agreement with those found for structurally related N‐aryl‐N‐benzylamides, are in the range ΔG≠ = 60.7‐89.6kJ mol−1. For some carbamates another conformational phenomenon has been observed, namely the hindered rotation about the carbonyl carbon–nitrogen bond, with a barrier to rotation corresponding to reported values for similar systems.
Massenspektren von sekundären Vinylcarbinolen
Authors: Kraft Manfred , Spiteller Gerhard 
Published: May 2005

AbstractDie Massenspektren sekundärer des Typs RCH(OH)CHCH2 zeigen die gleichen Bruchstücke wie die der isomeren Äthylketone RCOC2H5. Dies ist auf eine Umlagerung der Molekülionen der Vinylcarbinole in solche der Äthylktone vor Eintritt der Bruchstückbildung zurückzuführen. Die Massenspektren beider Verbindungsklassen unterscheiden sich nur geringfügig in den Intensitätswerten.
The fragmentation of organic molecules under electron‐IMPACT—II. The mass spectra of tetronic acid and some of its derivatives
Authors: Haynes L. J. , Kirkien‐Konasiewicz Alicja , Loudon A. G. , Maccoll Allan 
Published: May 2005

AbstractThe mass spectra of tetronic acid and of a number of its derivatives are recorded and discussed. Where necessary, the composition of the fragment ions has been checked by high resolution mass measurements. Fragmentation of the molecular ion is explained in terms of the rupture of a bond attached to C‐4, and the predominant routes for many of the compounds can be explained on the basis of two schemes, the first involving preliminary ketonisation of the molecular ion, followed by elimination of carbon monoxide, the second involving rupture of the C‐4R3 bond prior to elimination of carbon monoxide. Special structural features, however, provide alternative routes.
The fragmentation of tetronic acids and related compounds under electron‐impact
Authors: Ballantine J. A. , Fenwick R. G. , Ferrito V. 
Published: May 2005

AbstractThe mass spectra of two fungal metabolites, aspertetronin A and B, have been examined in conjunction with a series of tetronic acids and related compounds, and as a result the major modes of fragmentation of the tetronic acid ring system have been determined. Several substituent dependent rearrangements have also been recognised during this investigation which should prove useful in the structural elucidation of unknown compounds.
Etude Des Spectres de Masse Des Constituants Amers Des Simarubacées
Authors: Fourrey Jean‐Louis , Das Bhupesh C. , Polonsky Judith 
Published: May 2005

AbstractThe bitter compounds isolated from the species Simaroubaceae represent a new family of degraded triterpenoids. Ailanthone, glaucarubolone and chaparrinone having a C20 skeleton belong to this family and their structures were previously determined. Mass spectra of these compounds and some of their derivatives have now been studied in detail and the results obtained are discussed in this communication. The observed fragmentation pattern is characteristic of the structural features of this group of compounds.
Pyrolysis and mass spectra of some aromatic‐imides
Authors: Cotter J. L. , Dine‐Hart R. A. 
Published: May 2005

AbstractThe electron‐impact induced loss of CO2 from phthalanil and 4‐phthalimidobiphenyl is paralleled by the formation of large amounts of CO2 on pyrolysis. CO is also a major pyrolysis product, but the loss of CO from these compounds under electron‐impact is not an important fragmentation process.The mass spectra of meta and para‐chlorophthalanils show prominent [M  CO2] peaks but the corresponding peak for the ortho isomer is of relatively low intensity. CO and CO2 are the principal gaseous products of the thermal decomposition of o‐chlorophthalanil.
Observations on the mass spectrometry of monensin and related compounds
Authors: Chamberlin J. W. , Agtarap A. 
Published: May 2005

AbstractMonensin and nigericin are structurally related compounds belonging to a family of biologically active, polycylic, monocarboxylic acids produced by Streptomyces. Partial interpretation of their mass spectra has been achieved with the aid of high resolution data and by correlation with spectra of derivatives. These results have been applied to structure elucidation of several minor factors produced along with monensin. An interesting aspect of the mass spectrometry of these compounds is that their alkali‐metal salts are sufficiently volatile to yield mass spectra. Fragmentation of the salts is markedly different from that of the free acids and their derivatives. A scheme is proposed to account for the formation of a number of fragment ions which contain the metal atom.
The mass spectra of meliacins and related compounds—II: Meliacins lacking the ring d epoxide function
Authors: Loudon A. G. , Powell J. W. 
Published: May 2005

AbstractThe mass spectra of some 14,15‐deoxymeliacins are reported and discussed in relation to the previously published fragmentation patterns of the epoxymeliacins. The fragmentation patterns of a few compounds with structures closely related to those proposed for the principal ions in the spectra of the epoxymeliacins are also examined.
Mass spectrometry of piperidine nitroxides—A class of stable free radicals
Authors: Morrison A. , Davies A. P. 
Published: May 2005

AbstractThe 2,2,6,6‐tetramethylpiperidine nitroxides constitute a family of stable free radicals with electronic structures similar to that of nitric oxide. Ionization of the molecules by electron bombardment does not lead to the formation of a radical‐ion, as is the case with even‐electron neutral molecules, but instead yields either a biradical or an even‐electron molecular ion.The fragmentations of the ions arising from this ionization are described in detail. Accurate mass measurements on most ions (element mapping) and deuterium labelling, where appropriate, have been used to assist in the interpretation of the mass spectra. The observed elimination of nitric oxide from the molecular ions has photochemical analogies.
The electron‐impact‐induced fragmentation of 1,2,3‐benzotriazoles and some related compounds
Authors: Lawrence R. , Waight E. S. 
Published: May 2005

AbstractThe mass spectra of 1,2,3‐benzotriazole and some derivatives with substituents at the 1‐position and in the benzenering have been examined. The loss of N2from the molecularion is characteristic; loss of N2 plus the 1‐substituent is also common. Structures are proposed for these fragment ions. The relative ease of loss of N2, NO and NS from the molecular ions of benzotriazole, 2,1,3‐benzodiazole, 1,2,3‐ and 2,1,3‐benzothiadiazoles is compared.
Fragmentations de Molecules Aliphatiques Bifonctionnelles: Methoxyesters
Authors: Greff Marcel , Wolff Robert E. , Draffan G. H. , McCloskey James A. 
Published: May 2005

AbstractCertaines des fragmentations des méthoxyesters aliphatiques à longue chaíne nécessitent l'interation des deux fonctions: les deux éliminations d'alcool que subit l'ion par rupture en α de la fanction éther et comprenant le groupe ester, sont trés spécifiques: elles mettent en cause un atome d'hydrogéne en position adjacente au carbone qui porte le groupe méthoxyle.
The application of mass spectrometry to a quantitative characterisation of the electronic and steric effects in organic compounds—I: The transmission of substituent influence through the chain of conjugated double bonds
Authors: Zolotarev B. M. , Yanovskaya L. A. , Umirzakov B. , Chizhov O. S. , Kucherov V. F. 
Published: May 2005

AbstractThe mass spectra of polyenic compounds of the type RC6H4(CH=CH)nCOPh, n=1, R=H,p‐NMe2,p‐OH,p‐OMe,p‐Cl,p‐Br,p‐NO2,m‐NO2; n=2, R=H, p‐NMe2, p‐OMe,p‐Cl,p‐Br, p‐NO2; n = 3, R = H, p‐OMe,p‐Cl, p‐Br,p‐No2 have been measured. The ratio of the intensities of the common ion PhCO (m/e 105) to the intensities of the molecular ions for these series is correlated with the Hammett‐Brown equation with reaction constants p = 0.73 (when n = 1), 0.25 (when n =2), 0.11 (when n = 3). The transmission coefficients were calculated as π'=0.72,0.25 and 0.11 respectively [assuming p=1.01 for benzophenone series‐see M. M. Bursey and F. W. McLafferty, J. Am. Chem. Soc. 89, 1 (1967)]. The contributions of the inductive mesomeric direct polar conjugation and non‐additive interaction were calculated in accordance with the equation log Z/Z0= . It was found that the inductive influence as well as the mesomeric influence of substituents decreases rapidly with the increase in the number of double bonds in the chain. The direct polar effect has a very small value in all series for all substituents with the exeption of NMe2. Non‐additive interaction effects are large. They probably express the general influence of RC6H4(CH=CH)n on COPh.
Mass spectra of photoaddition products from methyl‐substituted maleic anhydrides and thiophen derivatives
Authors: Flores S. E. , Vélez M. , Rivas C. 
Published: May 2005

AbstractThe mass spectra of 1,2‐cycloaddition products obtained from the benzophenone photosensitized irradiation of 2,3‐dimethyl maleic and citraconic anhydride in several thiophen derivatives are prsented and discussed.
Rearrangements in the electron‐impact induced fragmentation of some β‐aroyl‐α‐methylpropionic acids
Authors: Buurmans H. M. A. , Van de Graaf B. , Kieboom A. P. G. 
Published: May 2005

AbstractA complex rearrangement on electron‐impact for β‐aroyl‐α‐methylpropionic acids, involving both hydrogen and hydroxy migration followed by loss of carbon monoxide and allyl radical, is described and discussed. The rearrangement process, resulting in an ion [ArCOOH2]+, is favoured by electron‐withdrawing substituents in the aromatic ring.
The mass spectra of 1,2,4‐triazines and related compounds
Authors: Palmer M. H. , Preston P. N. , Stevens M. F. G. 
Published: May 2005

AbstractThe mass spectra of monocyclic 1,2,4‐triazines and 1,2,4‐triazines fused to a pyrazole ring through a bridgehead nitrogen have been investigated: fragmentation pathways were elucidated by the use of metastable ions and high resolution mass measurements. The spectra of the monocyclic 1,2,4‐triazines indicate that loss of nitrogen from the molecular ions is a relatively unimportant feature. The decomposition modes of the bicyclic pyrazolo[3,2‐c]‐as‐triazines are sensitive to the nature of the substituent in the triazine ring.
Substituent effects on the mass spectra of substituted phenyl acetates
Authors: Gamble A. A. , Gilbert J. R. , Tillett J. G. 
Published: May 2005

AbstractThe mass spectra of a series of meta‐ and para‐substituted phenyl acetates have been examined. Substituent effects have been correlated with Δ (AP‐IP) values and by using the Harrison and Chin approach. The bond‐cleavage and rearrangement reactions of phenyl accetates are compared with the corresponding reactions of acetanilides and the differences attributed to the degree of transmission of polar effects in the two systems.
Mass spectra of some N‐amino compounds
Authors: Gillis R. G. 
Published: May 2005

AbstractN‐amino compounds on electron‐impact commonly lose NH from the molecular ion, and frequently lose N, NH2 and NH3. This behaviour contrasts with C‐amino compounds which mainly lose HCN and H2CN. The mass spectra of eight N‐amino compounds are recorded and discussed, together with some data from literature sources.
Comparative studies on photo‐ionization and electron‐impact ionization of peptide derivatives
Authors: Orlov V. M. , Varshavsky Ya. M. , Kiryushkin A. A. 
Published: May 2005

AbstractPhoto‐ionization (PI) mass spectrometry performed with a monochromatic photon beam was applied to a series of peptide derivatives. PI mass spectra of ten N‐acylpeptide methyl esters containing two to four residues of glycine, alanine, valine, leucine, proline, tryptophan, tyrosine, phenylalanine, methionine, carboxymethylcysteine, lysine and ornithine were studied. Comparative analysis of PI (10.2 eV) and electron‐impact ionization (EI) (70 eV) mass spectra shows the total number of peaks on PI to be much less than that obtained with EI, especially in the low m/e region (< 250 to 300). At the same time the relative abundance of ‘heavy’ ions, including molecular ions, is much higher in PI. The amino acid fragmentation pattern followed by N‐acylpeptide esters in PI was found to be the same as for EI.
The ion kinetic energy and mass spectra of isomeric methyl indoles
Authors: Safe S. , Jamieson W. D. , Hutzinger O. 
Published: May 2005

AbstractThe mass spectra of the seven isomeric methylindoles were recorded and the [metastable ion]/[daughter ion] ratios for the reactions m/e 130 → m/e 103 and m/e 103 → m/e 77 have been obtained. The ratios indicate that the decomposing [M — 1] ions (m/e 130) from the 4, 5, 6 and 7 isomers are energetically similar as are the [M — 1] ions from the 2 and 3 isomers. The results observed for the m/e → 103 m/e 77 reaction showed that the decomposing m/e 103 ions from the 2, 3, 4, 5, 6 and 7 isomers all have the same energy distribution. N‐Methylindole gave ratios which were similar to the 4 to 7 isomers at 70eV but different at 20 eV. The ion kinetic energy (IKE) spectra of all the isomeric methylindoles were also obtained and the results compared with the data obtained from the [metastable ion]/[daughter ion] approach. The results from the IKE spectra indicated that the energy distributions of the [M — 1] and [(M — 1) — HCN] ions from 1‐methylindole and the [(M — 1) — HCN] ions from 2‐methylindole could readily be distinguished from other isomers whose [metastable ion]/[daughter ion] ratios were similar. Thus by using both techniques certain ambiguities can be resolved.
Metastable transitions in the mass spectra of methyl and phenylthiohydantoin derivatives of amino acids
Authors: Sun T. , Lovins R. E. 
Published: May 2005

AbstractThe mass spectra of a number of methyl‐ and phenylthiohydantoin amino acid derivatives have been obtained. The major metastable transitions occurring in the mass spectra of these derivatives have been identified and measured. The major fragmentation pathways associated with the metastable transitions have been outlined and are discussed for each group of compounds. Inspection of the metastable data has shown that there is at least one unique metastable transition occurring for each thiohydantoin derivative which may be used to uniquely identify that derivative in the presence of a mixture of thiohydantoin derivatives obtained from the Edman degradation of a peptide or protein. The use of metastable ions to uniquely identify thiohydantoin derivatives in mixtures has proven useful in the identification of the MTH and PTH derivatives of glycine whose molecular ions are not unique and for resolving such ambiguities as occur for example in the mixture of leucine and isoleucine.
High resolution mass spectrometry. Bufadienolides I
Authors: Brown Peter , Kamano Yoshiaki , Pettit George R. 
Published: May 2005

AbstractComplete low resolution mass spectra and some high resolution data are presented and discussed for a series of naturally occurring 14β‐hydroxy bufadienolides (toad venoms) and their derivatives, but excluding compounds with a 14β,15β‐epoxy group. The bufadienolides employed were bufalin, bufotalin, gamabufotalin, telocinobufagin, arenobufagin, 3β‐acetoxybufotalien, 3β‐acetoxyhellebrigenin, 3β‐acetoxybufalin, 3‐ketobufalin, 14‐anhydrobufalin, 3β‐acetoxy‐15‐ketobufalin and 15α‐hydroxybufalin. The relatively unsaturated 2‐pyrone functionality at C‐17β has been used as an integral label to distinguish (from elemental composition data) ions containing it, from those coming from other parts of the molecule that do not. Structural ‘ion types’ are proposed to interpret this spectral data, and the prognosis for structure elucidation of other bufadienolides by high resolution mass spectrometry appears good.
Variation of fragmentation with ring size in cyclic α‐amino acids
Authors: Coulter A. W. , Fenselau C. C. 
Published: May 2005

AbstractHigh resolution mass measurements, defocused metastable ion detection and deuterium labeling experiments have been employed in an investigation of the electron‐impact induced decomposition of a series of carbocyclic amino acids, which varied in ring size from three to eight carbon atoms. About 50 per cent of the total ion current is carried by [M  COOH]+ ions in the spectra obtained from compounds with five to eight carbon atoms in the ring. This is analogous to the fragmentation of the open chain naturally occurring amino acids. The behavior of the compounds with the two smallest rings is anomalous, reflecting to a larger extent the influence of the ring itself. Special attention has been given the loss of H2O and NH4 from ionized species of 1‐aminocyclopropanecarboxylic acid.
The effect of stereochemistry on the mass spectra of the bis(trimethyl‐silyl) esters of maleic and fumaric acids
Authors: Large R. , Saunders K. J. 
Published: May 2005

AbstractThe mass spectra of the bis(trimethylsilyl) esters of maleic and fumaric acids provide a simple and particularly striking example of the influence of stereochemistry on the electron‐impact‐induced fragmentation of organic molecules. The results provide evidence for the structural significance of the m/e 147 ion, which is considerably more intense in the maleate spectrum than in the fumurate spectrum.
Intramolecular amide‐amide interaction in the mass spectra of some geometric isomers
Authors: Holmes J. L. 
Published: May 2005

AbstractThe mass spectra of maleic, fumaric, citraconic, mesaconic and itaconic diamides have been studied. In the molecular ions of the cis isomers, amide‐amide interaction does take place, analogous to but less pronounced than, the carboxyl‐carboxyl interaction of the corresponding acids.In spite of the weaker interaction a prominent loss of CONH from the molecular ion of a diamide would be strong evidence in support of a cis or similarly rigid geometrical arrangement of the amide groups. The mass spectra of maleic and fumaric nitriles are also reported.
Specific and random processes in the fragmentation of cyclohexanol
Authors: Holmes J. L. , McGillivray D. , Rye R. T. B. 
Published: May 2005

AbstractThe mass spectra of cyclohexanol and eleven deuterated analogues have been studied. Detailed mechanisms, consistent with peak intensity and defocused metastable abundance data, have been proposed for the loss of water from the molecular ion and for the subsequent loss of a methyl radical. The importance of specific eliminations and the absence of any processes involving complete hydrogen atom scrambling in these fragmentations has been demonstrated. Scrambling has also been shown to be absent in the formation of the base peak m/e 57, the [C3H5O]+ ion.
Elektronenstossinduzierte Fragmentierung von Acetylenverbindungen—VI: Struktur und Bildungsenthalpie der Ionen [C11H9]+ und [C9H7]+
Authors: Schwarz Helmut , Bohlmann Ferdinand 
Published: May 2005

AbstractDie Erscheinungspotentiale für [C11H9]+ aus 1‐bzw, 2‐(Chlormethyl)‐Naphthalin und 1‐Chlor‐phenyl‐(5)‐penten‐(2)‐in‐(4) und für [C9H7]+ aus Inden, Phenylpropin und Phenyl‐(5)‐penten‐(2)‐in‐(4)ol‐(1) werden mit thermochemischen Daten korreliert, um die Bildungsenthalpien der genannten Fragment‐Ionen zu erhalten. Ein Vergleich dieser Bildungsenthalpien mit den Enthapiewerten hypothetischer Modellstrukturen ergibt, dass das IOn [C11H9]+ wahrscheinlich am besten als Benztropylium‐Ion und das Ion [C11H9]+ enweder als ein Äthinyl‐Tropylium‐Ion oder als ein Phenylcyclopropenyl‐Kation wiedergegeben wird. Offenkettige Strukturen Können in allen untersuchten Fällen ausgeeschlossen werden.
Ion‐molecule reactions of a metalloporphyrin with common perfluoro mass standards
Authors: Rosenthal David , Hopf Frederick R. , Whitten David G. , Bursey Maurice M. 
Published: May 2005

AbstractThe ruthenium porphyrin carbonyl (I) reacts with perfluorokerosene and perfluorotributylamine to give ions of the type [M – CO + CnF2n], n = 1 to 4.