International Journal of Mass Spectrometry and Ion Processes最新文献

{"title":"Deuterium isotope effects on gas phase ion-molecule hydrogen-bonding interactions: Alcohol-alkoxide and alcohol-chloride adduct ions","authors":"F.E. Wilkinson,&nbsp;M. Peschke,&nbsp;J.E. Szulejko,&nbsp;T.B. McMahon","doi":"10.1016/S0168-1176(98)00142-6","DOIUrl":"10.1016/S0168-1176(98)00142-6","url":null,"abstract":"<div><p>Fourier Transform Ion Cyclotron Resonance (FT-ICR) and High Pressure Mass Spectrometric (HPMS) measurements of the deuterium isotope effect and kinetics of adduct ion formation have been used to probe the nature of the potential describing the motion of the hydrogen in gas phase ion-molecule hydrogen-bonding interactions. Hydrogen-bonding systems reported in this paper are alkoxide ion and chloride ion solvated by one molecule of alcohol, ROH●OR^- and ROH●Cl^-. Significant differences in the isotope effects were observed for the two systems. These differences are explained on the basis of the differing hydrogen bond strengths of the adduct ions, and the ability of the chloride ion to partake in multiple site, or chelate, interactions. In addition, HPMS studies of the kinetics of the reaction of CH₃O⁻ with CH₃OH reveal that a double minimum potential energy surface may be appropriate for describing the adduct ion formation. These experimental studies have been supplemented by ab initio calculations to determine adduct ion structures as well as to permit statistical thermodynamic calculations of the isotope effect.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 1","pages":"Pages 225-240"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00142-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75617640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of basic site proximity on deprotonation and hydrogen/deuterium exchange reactions for model dodecapeptide ions containing lysine and glycine","authors":"Xin Zhang,&nbsp;Nigel P Ewing,&nbsp;Carolyn J Cassady","doi":"10.1016/S0168-1176(98)00124-4","DOIUrl":"10.1016/S0168-1176(98)00124-4","url":null,"abstract":"<div><p>The effects of basic site proximity on gas-phase deprotonation and hydrogen/deuterium (H/D) exchange reactions were investigated for three model dodecapeptide ions in a Fourier transform ion cyclotron resonance mass spectrometer. Each peptide contained four high basicity lysine (K) residues and eight low basicity glycine (G) residues; however, the ordering of the residues differed. In the deprotonation studies, ‘fully protonated’ peptide ions, [M + 4H]⁴⁺, where M = (KGG)₄, (K₂G₄)₂, and K₄G₈, were reacted with reference compounds of known basicities.</p><p>Reaction efficiencies were in the order: [K₄G₈ + 4H]⁴⁺ &gt; [(K₂G₄)₂ + 4H]⁴⁺ ∼ [(KGG)₄ + 4H]⁴⁺. The facile reaction of [K₄G₈ + 4H]⁴⁺ is consistent with this ion having the highest Coulomb energy. For gas-phase H/D exchange reactions with <em>d</em>₄-methanol, [K₄G₈ + 4H]⁴⁺ has the fastest exchange rate and undergoes the largest number of exchanges; 22 of the 26 labile hydrogens exchanged within the timescale studied. In contrast, [(KGG)₄ + 4H]⁴⁺ and [(K₂G₄)₂ + 4H]⁴⁺ reacted more slowly, but at similar rates, with a maximum of 14 observed exchanges for both ions. Molecular dynamics calculations were conducted to gain insights into conformations. In the lowest energy structures for [(KGG)₄ + 4H]⁴⁺ and [(K₂G₄)₂ + 4H]⁴⁺, the lysine <em>n</em>-butylamino chains stretch out to minimize Coulomb energy; there is little or no intramolecular hydrogen bonding involving the protonated amino groups. In contrast, for [K₄G₈ + 4H]⁴⁺, the proximity of the basicity residues makes minimization of the Coulomb energy difficult; instead, the structure becomes more compact with stabilization of the protonated amino groups by extensive intramolecular hydrogen bonding to heteroatoms in the peptide backbone. The calculated structures suggest that, in the H/D exchange reactions, the compact conformation of [K₄G₈ + 4H]⁴⁺ allows stabilization of the methanolpeptide intermediate by hydrogen bonding, thus lowering the barrier to proton transfer within the complex. The diffuse conformations of [(KGG)₄ + 4H]⁴⁺ and [(K₂G₄)₂ + 4H]⁴⁺ have lower Coulomb energies and fewer avenues for hydrogen bonding with methanol, which may limit their rate and extent of exchange.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 1","pages":"Pages 159-171"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00124-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84294921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Partial doubly differential cross-sections for the ionization of H2 by electron impact","authors":"Satyendra Pal ,&nbsp;Satya Prakash ,&nbsp;Shyam Kumar","doi":"10.1016/S0168-1176(98)00105-0","DOIUrl":"10.1016/S0168-1176(98)00105-0","url":null,"abstract":"<div><p>Partial doubly differential cross-sections (PDDCS), as a function of secondary electron energy for the H₂ molecule leading to direct and dissociative ionizations have been calculated using a semi-empirical approach. The incident electron energies used are 100, 500 and 1000 eV. The calculations are made at scattering angles of 30°, 60° and 90°. The present results are compared with the available experimental and theoretical data.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 3","pages":"Pages 247-252"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00105-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83840416","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Substituent effects on the gas-phase basicities of 1-arylpropynes and 1-aryl-3,3-dimethylbutynes effects of the β-alkyl groups on the resonance demand of vinyl cations","authors":"Takatsugu Matsumoto,&nbsp;Shinjiro Kobayashi,&nbsp;Masaaki Mishima,&nbsp;Yuho Tsuno","doi":"10.1016/S0168-1176(98)00119-0","DOIUrl":"10.1016/S0168-1176(98)00119-0","url":null,"abstract":"<div><p>The relative stabilities of 1-aryl-2-methylvinyl cations (1) and 1-aryl-2-<em>t</em>-butylvinyl cations (II) were determined by measuring the proton-transfer equilibria of 1-arylpropynes and 1-aryl-3,3-dimethylbutynes in the gas phase. The stabilities of 1-phenyl-2-methylvinyl cation and 1-phenyl-2-<em>t</em>-butylvinyl cation were found to be 1.8 and 5.5 kcal mol⁻¹ higher than that of 1-phenylvinyl cation, respectively. The substituent effects on the stability of these vinyl cations could be correlated in terms of the Yukawa-Tsuno equation, giving an <em>r</em>⁺ of 1.13 and a <em>p</em> of −9.5 for I, and 1.03 and −9.4 for II. Combined with the previous results, it was found that the <em>r</em>⁺ value decreases with the increase in stability of the unsubstituted member of the respective vinylic carbocations while the <em>p</em> values remain constant for a series of the phenylvinyl cation system. This indicates that the π-delocalization of the positive charge into the aryl π-system decreases with the stabilization of a vinyl cation by the β-substituent. This trend is consistent with the observation for a series of ordinary sp²-hybridized benzylic carbocations. In addition, it has been shown that both sp- and sp²-carbocation systems obey a single linear relationship between the <em>r</em>⁺ values and carbocation stabilities of the unsubstituted member of respective series. This result clearly demonstrates a continuous spectrum of varying resonance demands characteristic of the stabilities of carbocations. It was concluded that the π-delocalization mechanism in the vinyl cation system has no unique feature but it is a part of a continuous spectrum of resonance demands of varying benzylic carbocations.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 1","pages":"Pages 41-49"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00119-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86818869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Estimation of ionization energies of substituted anilines by the kinetic method","authors":"Jeff W. Denault,&nbsp;Guodong Chen,&nbsp;R.Graham Cooks","doi":"10.1016/S0168-1176(98)00118-9","DOIUrl":"10.1016/S0168-1176(98)00118-9","url":null,"abstract":"<div><p>Ionization energy (IE) determinations by the kinetic method are extended to a functionalized class of compounds: substituted anilines. The radical-cation-bound dimers of substituted anilines were generated under self-CI conditions and the dissociation products examined using two collision energies, 2 and 10 eV, in a triple quadrupole tandem mass spectrometer. Using <em>N</em>,<em>N</em>-diethylaniline (IE = 6.98 ± 0.02 eV), 3,5-dimethylaniline (IE = 7.2 eV), <em>N</em>-methylaniline (IE = 7.33 ± 0.02 eV), 2-methylaniline (IE = 7.44 ± 0.02 eV), 3-methylaniline (IE = 7.50 ± 0.02 eV), aniline (IE = 7.720 ± 0.002 eV), and benzylamine (IE = 8.64 ± 0.05 eV) as reference compounds, a linear correlation is observed between the natural log of the ratio of the fragment ion abundances versus ionization energy for each collision energy. The effective temperature of the activated cluster ions rises from 1180 to 1470 K as the collision energy is raised from 2 to 10 eV. The average estimated IE values for 4-methoxyaniline, 2-methoxyaniline, 4-methylaniline, 3-chloroaniline and 3-fluoroaniline are determined to be 7.00 ± 0.15 eV, 7.19 ± 0.07 eV, 7.37 ± 0.07 eV, 8.27 ± 0.08 eV, 8.37 ± 0.07 eV respectively.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 1","pages":"Pages 205-213"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00118-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86218260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gas-phase acidities of o-, m- and p-dehydrobenzoic acid radicals. Determination of the substituent constants for a phenyl radical site","authors":"Paul G. Wenthold ,&nbsp;Robert R. Squires","doi":"10.1016/S0168-1176(98)00120-7","DOIUrl":"10.1016/S0168-1176(98)00120-7","url":null,"abstract":"<div><p>Reaction of CO₂ with <em>o</em>-, <em>m</em>-, and <em>p</em>-benzyne radical anions in the gas phase produces <em>o</em>-, <em>m</em>-, and <em>p</em>-dehydrobenzoate radical anions, respectively. The (oxygen) gas-phase basicities of these ions, which are equivalent to the gas-phase acidities of the corresponding dehydrobenzoic acid radicals, <em>ΔG</em>_acid(<em>o</em>-, <em>m</em>-, or <em>p</em>-C₆H₄CO₂-H), have been determined with a flowing afterglowtriple quadrupole apparatus by means of the kinetic method. The measured values are (in kcal mol⁻¹): <em>ΔG</em>_acid(<em>o</em>-C₆H₄CO₂H) = 330.4 ± 0.4, <em>ΔG</em>_acid(<em>m</em>-C₆H₄CO₂H) = 330.2 ± 0.4, and <em>ΔG</em>_acid(<em>p</em>-C₆H₄CO₂H) = 331.6 ± 0.4 kcal mol⁻¹. All three radicals are more acidic than benzoic acid (<em>ΔG</em>_acid = 333.1 ± 2.0 kcal mol⁻¹). The measured gas-phase acidities for the meta and para isomers suggest values for the resonance-effect substituent constant, <em>σ</em>_R, and the field/inductive effect substituent constant, <em>σ</em>_F, for a phenyl radical site of - 0.47 and 0.57, respectively. This classifies a phenyl radical site as a strong inductive withdrawing, and strong resonance donating substituent. Density functional calculations of the gas-phase acidities of dehydrobenzoic acids are in good agreement with the experimental results. The increased acidities of the dehydrobenzoic acids are shown to arise from a balance between the electron withdrawing effect of the electronegative radical site, and a compensating polarization of the π system which mimics the effect of a resonance donor group located at the radical carbon.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 1","pages":"Pages 215-224"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00120-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76207072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the acidity and basicity of azoles: the Taft scheme for electrostatic proximity effects","authors":"J. Catalán,&nbsp;J. Palomar,&nbsp;J.L.G. de Paz","doi":"10.1016/S0168-1176(98)00111-6","DOIUrl":"10.1016/S0168-1176(98)00111-6","url":null,"abstract":"<div><p>A theoretical study of the acid-base behavior of azole systems was carried out using density functional theory (B3LYP). The results were consistent with experimental measurements of the systems in the gas phase. A two-way linear relationship between theoretical and experimental data is established that links the acid and base ranges for the neutral forms. The applicability of the Taft model for electrostatic proximity effects to this type of compounds is demonstrated.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 1","pages":"Pages 51-59"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00111-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76666379","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaporation of charged fine droplets","authors":"Atsumu Hirabayashi","doi":"10.1016/S0168-1176(97)00237-1","DOIUrl":"10.1016/S0168-1176(97)00237-1","url":null,"abstract":"<div><p>At about the minimum flow rate, mono-disperse charged droplets have been produced by electrospray from an aqueous solution of trifluoroacetic acid. Charged droplets and ions formed from the droplets were passed through a heated copper tube and then analyzed with a differential mobility analyzer. In the mobility spectra it was found that with increasing temperature the current of the charged droplet peak at 3.75 × 10⁻⁵m² V⁻¹ s⁻¹ decreases and finally disappears, while that of the ion peak at 7.20 × 10⁻⁵m² V⁻¹ s⁻¹ decreases much less. This result shows that ions are formed from heated droplets. The electric field at the droplet surface was determined as (1.32 ± 0.09) × 10⁹V m⁻¹.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 3","pages":"Pages 241-245"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(97)00237-1","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74827647","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fast-ion-induced surface tracks in bioorganic films","authors":"J. Eriksson,&nbsp;J. Rottler,&nbsp;C.T. Reimann","doi":"10.1016/S0168-1176(98)00123-2","DOIUrl":"10.1016/S0168-1176(98)00123-2","url":null,"abstract":"<div><p>Surface tracks, induced by single grazing incidence 55 MeV ¹²⁷I ions, incident on various bioorganic films, were studied by intermittent contact (tapping-mode) scanning force microscopy (SFM). Targets composed of biomolecules with different masses (10² − 10⁵u) were employed. Surface tracks appeared as craters with raised rims and tails. In SFM, probe-tip-induced deformation of surface features under study is a possible complication, since it can lead to false imaging. In tapping-mode-SFM, larger amounts of tip oscillation attenuation with respect to the free amplitude imply greater tip-surface contact force. We found that reproducible track size results were obtained with a low attenuation (&lt; 4%), and track dimensions on the various surfaces could be compared quantitatively. The crater lateral dimensions decreased with increased target molecular mass. For surfaces composed of large protein molecules the craters are smaller than the molecules, which implies an upper mass limit for the detection of intact proteins by PDMS. The measurements were compared with various sputtering model predictions. A pressure-pulse model calculation assuming extensive cluster ejection showed fair agreement with observed crater widths and lengths.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 3","pages":"Pages 293-308"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00123-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88228180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Superacid chemistry in the gas phase: Dissociative proton attachment to halomethanes","authors":"J.-L.M. Abboud ,&nbsp;O. Castaño ,&nbsp;J. Elguero ,&nbsp;M. Herreros ,&nbsp;N. Jagerovic ,&nbsp;R. Notario ,&nbsp;K. Sak","doi":"10.1016/S0168-1176(98)00110-4","DOIUrl":"10.1016/S0168-1176(98)00110-4","url":null,"abstract":"<div><p>The standard Gibbs energy changes for the halide transfer processes in the gas phase have been determined by means of Fourier transform ion cyclotron resonance mass spectrometry (FT ICR): <span><span><span><math><mtext>1-</mtext><mtext>Ad</mtext><mtext>-</mtext><mtext>X(g)</mtext><mtext>+</mtext><mtext>R</mtext><msup><mi></mi><mn>+</mn></msup><mtext>(</mtext><mtext>g</mtext><mtext>)→1-</mtext><mtext>Ad</mtext><msup><mi></mi><mn>+</mn></msup><mtext>(</mtext><mtext>g</mtext><mtext>)+</mtext><mtext>R</mtext><mtext>-</mtext><mtext>X(g)</mtext></math></span></span></span> X = Halogen; l-Ad = 1-Adamantyl; R-X = CCl₄ (1), CBr₄ (2), CI₄ (3) and CBr₃F (4).</p><p>To this end, systematic use was made of the dissociative proton attachment method (DPA) [J-L.M. Abboud et al., J. Am. Chem. Soc. 116 (1994) 2486–2492.], which allowed one to experimentally determine the onsets for reactions: <span><span><span><math><mtext>R-X(g)</mtext><mtext>+</mtext><mtext>BH</mtext><msup><mi></mi><mn>+</mn></msup><mtext>(</mtext><mtext>g</mtext><mtext>)→</mtext><mtext>R</mtext><msup><mi></mi><mn>+</mn></msup><mtext>(</mtext><mtext>g</mtext><mtext>)+</mtext><mtext>HX(g)</mtext><mtext>+</mtext><mtext>B(g)</mtext></math></span></span></span> R = CCl₃, CBr₃, CI₃, CBr₂F, 1-Ad.</p><p>In the case of 4, two different onsets were determined, respectively, corresponding to the formation of CBr₂F⁺(g) and CBr₃⁺ (g).</p><p>The thermodynamics of several reactions (see the first equation above) were studied at the MP2/6–31G(d) level. The results agree very satisfactorily with the experimental results.</p></div>","PeriodicalId":14197,"journal":{"name":"International Journal of Mass Spectrometry and Ion Processes","volume":"175 1","pages":"Pages 35-40"},"PeriodicalIF":0.0,"publicationDate":"1998-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0168-1176(98)00110-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90861437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}