Neurolysin knockout mice generation and initial phenotype characterization

The oligopeptidase neurolysin (EC 3.4.24.16; Nln) was first identified in rat brain synaptic membranes and shown to ubiquitously participate in the catabolism of bioactive peptides such as neurotensin and bradykinin. Recently, it was suggested that Nln reduction could improve insulin sensitivity. Here, we have shown that Nln knockout mice (KO) have increased glucose tolerance, insulin sensitivity and gluconeogenesis. KO mice have increased liver mRNA for several genes related to gluconeogenesis. Isotopic label semi-quantitative peptidomic analysis suggests increase in specific intracellular peptides in gastrocnemius and epididymal adipose tissue, which likely is involved with the increased glucose tolerance and insulin sensitivity in the KO mice. These results suggest the exciting new possibility that Nln is a key enzyme for energy metabolism and could be a novel therapeutic target to improve glucose uptake and insulin sensitivity

The Ionized Methylene Transfer From The Distonic Radical Cation +ch 2-o-ch 2 To Heterocyclic Compounds. A Pentaquadrupole Mass Spectrometric Study

Ion-molecule reactions of the mass-selected distonic radical cation +CH 2-O-CH 2 · (1) with several heterocyclic compounds have been investigated by multiple stage mass spectro- metric experiments performed in a pentaquadrupole mass spectrometer. Reactions with pyridine, 2-, 3-, and 4-ethyl, 2-methoxy, and 2-n-propyl pyridine occur mainly by transfer of CH 2 +· to the nitrogen, which yields distonic N-methylene-pyridinium radical cations. The MS 3 spectra of these products display very characteristic collision-induced dissociation chemistry, which is greatly affected by the position of the substituent in the pyridine ring. Ortho isomers undergo a δ-cleavage cyclization process induced by the free-radical character of the N-methylene group that yields bicyclic pyridinium cations. On the other hand, extensive CH 2 +· transfer followed by rapid hydrogen atom loss, that is, a net CH + transfer, occurs not to the heteroatoms, but to the aromatic ring of furan, thiophene, pyrrole, and N-methyl pyrrole. The reaction proceeds through five- to six-membered ring expansion, which yields the pyrilium, thiapyrilium, N-protonated, and N-methylated pyridine cations, respectively, as indicated by MS 3 scans. Ion 1 fails to transfer CH 2 +· to tetrahydrofuran, whereas a new α-distonic sulfur ion is formed in reactions with tetrahydrothiophene. Unstable N-methylene distonic ions, likely formed by transfer of CH 2 +· to the nitrogen of piperidine and pyrrolidine, undergo rapid fragmentation by loss of the α-NH hydrogen to yield closed-shell immonium cations. The most thermodynamically favorable products are formed in these reactions, as estimated by ab initio calculations at the MP2/6-31G(d,p)//6-31G(d,p) + ZPE level of theory. © 1995 American Society for Mass Spectrometry.6755456

Extensional And Shear Viscosity Of Acidified Amaranth Starch-sodium Caseinate Suspensions [viscosidade Extensional E Em Cisalhamento De Suspensões Acidificadas De Amido De Amaranto E Caseinato De Sódio]

Extensional and shear viscosity of acidified amaranth starch-sodium caseinate suspensions were evaluated. Mixed systems of amaranth starchsodium caseinate acidified with glucone-delta-lactone (GDL) were studied using rheological measurements under biaxial compression and shear. The effects of the acidification rate (slow and fast) and final pH (neutral and isoelectric point of casein) were evaluated considering the interactions between biopolymers and their influence on the rheological parameters. All samples showed shear thinning behavior, but the addition of sodium caseinate in the starch suspensions at neutral pH promoted a negative effect on the apparent viscosity. The acidified samples showed an increase in the complexity of the system due to the formation of a network of starch-casein, but the force required to flow was always higher for samples containing higher concentrations of caseinate. These results show that the protein aggregation and gelation promoted by acidification prevented the microphase separation. The network was stronger in slowly gelled systems due to the formation of a more organized protein network. Although the technique of biaxial compression was not considered adequate to evaluate certain systems, our results showed that it can be a practical and efficient way to measure the rheological behavior.293587596Abu-Jdayil, H., Mohameed, H., Eassa, A., Rheology of wheat starch-milk-sugar systems: Effect of starch concentration, sugar type and concentration, and milk fat content (2004) Journal of Food Engineering, 64 (2), pp. 207-212Achayuthakan, P.E., Suphantharika, M., Pasting and rheological properties of waxy corn starch as affected by guar gum and xanthan gum (2008) Carbohydrate Polymers, 71 (1), pp. 9-17(1997) Official methods of analysis, , Association of Official Analytical Chemists - AOAC, 16 ed. Washington, D. CBaroni, A.F., Caracterização reológica de requeijão cremoso tradicional e com teor reduzido de gordura: Viscosidade extensional e em cisalhamento (1999) Brazilian Journal of Food Technology, 2 (1), pp. 21-29Bertolini, A.C., Lawrence, K.C., Mieke, E., Some rheological properties of sodium caseinate - starch gels (2005) Journal of Agricultural and Food Chemistry, 53 (6), pp. 2248-2254Bhosale, R., Singhal, R., Effect of octenylsuccinylation on physicochemical and functional properties of waxy maize and amaranth starches (2007) Carbohydrate Polymers, 68 (3), pp. 447-456Braga, A.L.M., Cunha, R.L., The effect of sucrose on unfrozen water and syneresis of acidified sodium caseinate-xanthan gels (2005) International Journal of Biological Macromolecules, 36 (1-2), pp. 33-38Braga, A.L.M., Menossi, M., Cunha, R.L., The effect of the glucono-delta-lactone/caseinate ratio on sodium caseinate gelation (2006) International Dairy Journal, 16 (5), pp. 389-398Calzetta, R.A., Aguerre, R.J., Suarez, C., Analysis of the sorptional characteristics of amaranth starch (1999) Journal of Food Engineering, 42 (1), pp. 51-57Campanella, O., Elongation viscosity measurement of melting American processed cheese (1987) Journal Food Science, 52 (5), pp. 1249-1251Campanella, O., Peleg, M., Squeezing flow viscosimetry of peanut butter (1987) Journal Food Science, 52 (1), pp. 180-184Campanella, O., Peleg, M., Squeezing flow viscometry for nonelastic semiliquid foods - theory and applications (2002) Critical Reviews in Food Science and Nutrition, 42 (3), pp. 241-264Cavallieri, A.L.F., (2003) Influência da desnaturação térmica e do pH sobre as propriedades reológicas da proteína dos soro e sua compatibilidade com a xantana, p. 109. , Campinas, Dissertação (Mestrado em Engenharia de Alimentos) - Universidade Estadual de Campinas - UNICAMPCavallieri, A.L.F., Whey protein interactions in acidic cold-set gels at different pH values (2007) Lait, 87 (6), pp. 535-554Cavallieri, A.L.F., Cunha, R.L., The effects of acidification rate, pH and ageing time on the acidic cold set gelation of whey proteins (2008) Food Hydrocolloids, 22 (3), pp. 439-448Cèsaro, A., Thermodynamic behavior of mixed biopolymers in solution and in gel phase (1999) Thermochimica Acta, 388 (1-2), pp. 143-153Chen, S., Dickinson, J.S., On the temperature reversibility of the viscoelasticity of acid-induced sodium caseinate emulsion gels (2000) International Dairy Journal, 10 (8), pp. 541-549Daniel, A.P., Fracionamento a seco da farinha de aveia e modificação química da fração rica em amido (2006) Ciência e Tecnologia de Alimentos, 26 (4), pp. 936-943Dolz, M., Influence of xanthan gum and locust bean gum upon flow and thixotropic behaviour of food emulsions containing modified starch (2007) Journal of Food Engineering, 81 (1), pp. 179-186Hoffner, B., Gerhards, C., Peleg, M., Imperfect lubrication squeezing flow viscometry for foods (1997) Rheologica Acta, 36 (6), pp. 686-693Horne, D.S., Casein micelles as hard spheres: Limitations of the model in acidified gel formation (2003) Colloids and Surfaces A: Physicochemical and Engineering Aspects, 213 (2), pp. 255-263Jackson, A.P., Lin-Liu, X., Paton, R., Squeeze flow characterization of thermoplastic polymer (2006) Composite Structures, 75 (1-4), pp. 179-184Ju, Z.Y., Kilara, A., Gelation of ph-aggregated whey protein isolate solution induced by heat, protease, calcium salt, and acidulant (1998) Journal of Agricultural and Food Chemistry, 46 (5), pp. 1830-1835Martínez, C., Cuevas, F., (1989) Evaluación de la calidad culinaria y molinaria del arroz, p. 75. , Cali: CIATMoresi, M., Spinose, M., Engineering factors in the production of concentrates fruit juices (1980) Journal of Food Technology, 15 (3), pp. 265-276Munhoz, M.P., Weber, F.H., Chang, Y.K., Influência de hidrocolóides na textura de gel de amido de milho (2004) Ciência e Tecnologia de Alimentos, 24 (3), pp. 403-406Nayouf, M., Loisel, C., Doublier, J.L., Effect of thermomechanical treatment on the rheological properties of crosslinked waxy corn starch (2003) Journal of Food Engineering, 59 (2-3), pp. 209-219Nguyen, Q.D., Jensen, C.T.B., Kristensen, P.G., Experimental and modelling studies of the flow properties of maize starch pastes (1998) Chemical Engineering Journal, 70 (2), pp. 165-171Nicolas, Y., Microrheology: New methods to approach the functional properties of food (2003) Food Hydrocolloids, 17 (6), pp. 907-913Nuessli, J., Rheology and structure of amylopectin potato starch. Dispersions without and with emulsifier addition (2000) Starch - Stärke, 52 (1), pp. 22-27Pampa, N.B.Q., (2003) Estudo do comportamento reológico em cisalhamento estacionário e oscilatório de suspensões de amido de amaranto, p. 88. , Campinas, Dissertação (Mestrado em Engenharia de Alimentos) - Universidade Estadual de Campinas - UNICAMPPereira, L.B., (2004) Caracterização de suspensões e géis de amido de amaranto: Efeito da adição de sacarose e NaCl nas propriedades reológicas e térmicas, p. 142. , Campinas, Dissertação (Mestrado em Engenharia de Alimentos) - Universidade Estadual de Campinas - UNICAMPSgarbieri, V.C., Propriedades funcionais de proteínas em alimentos (1998) Boletim da Sociedade Brasileira de Tecnologia de Alimentos, 32 (1), pp. 105-126Silva, G.O., Características físico-químicas de amidos modificados de grau alimentício comercializados no Brasil (2006) Ciência e Tecnologia de Alimentos, 26 (1), pp. 188-197Song, Y., Wang, Z., Zheng, Q., Equibiaxial extensional flow of wheat gluten plasticized with glycerol (2007) Food Hydrocolloids, 21 (8), pp. 1290-1295Song, Y., Wang, Z., Zheng, Q., Equibiaxial extensional deformation and stress relaxation of glycerol plasticized wheat gluten at different concentrations (2008) Food Hydrocolloids, 22 (3), pp. 414-420Syrbe, A., Bauer, W.J., Klostermeyer, N., Polymer science concepts in dairy systems - an overview of milk protein and food hydrocolloid interation (1998) International Dairy Journal, 8 (3), pp. 179-193Suwonsichon, T., Peleg, M., Imperfect squeezing flow viscometry for commercial refried beans (1999) Food Science and Technology International, 5, pp. 159-166Suwonsichon, T., Peleg, M., Rheological characterization of almost intact and stirred yogurt by imperfect squeezing flow viscometry (1999) Journal of the Science of Food and Agriculture, 79 (6), pp. 911-921Tapia-Blácido, D., Sobral, P.J., Menegalli, F.C., Development and characterization of biofilms based on amarant flour (Amaranthus caudatus) (2005) Journal of Food Engineering, 67 (1-2), pp. 215-223Tárrega, A., Vélez-Ruiz, J.F., Costell, E., Influence of milk on the rheological behaviour of cross-linked waxy maize and tapioca starch dispersions (2005) Food Reserch International, 38 (7), pp. 759-768Tecante, A., Doublier, J.L., Steady flow and viscoelastic behavior of crosslinked waxy corn starch-k-carrageenan pastes and gels (1999) Carbohydrate Polymers, 40 (3), pp. 221-231Teli, M.D., Rheological properties of Amaranthus paniculates (Rajgeera) starch vis-à-vis maize starch (2007) Carbohydrate Polymers, 69 (1), pp. 116-122Terpstra, M.E.J., Janssen, A.M., van de Linden, E., Exploring imperfect squeezing flow measurements in a teflon geometry for semisolid foods (2007) Journal of Food Science, 72 (9), pp. E492-E502Tolstoguzov, V., Thermodynamic considerations of starch functionality in foods (2003) Carbohydrate Polymers, 51 (1), pp. 99-111Tolstoguzov, V., Thermodynamic considerations on polysaccharide functions. Polysaccharides came first (2003) Carbohydrate Polymers, 54 (3), pp. 371-380Valim, M.D., Cavallieri, A.L.F., Cunha, R.L., Whey protein/ arabic gum gels formed by chemical or physical gelation process (2009) Food Biophysics, 4 (1), pp. 23-31Walstra, P., Casein sub-micelles: Do they exist? (1999) International Dairy Journal, 9 (3-6), pp. 189-192Weinbreck, F., Complex coacervation of whey proteins and gum arabic (2003) Biomacromolecules, 4 (2), pp. 293-303Wu, H., Corke, H., Genetic diversity in physical properties of starch from a world collection of amaranthus (1999) Cereal Chemistry, 76 (6), pp. 877-88

Gaseous Sf3 +: An Efficient Electrophilic Monofluorinating Agent For Five-membered Heteroaromatic Compounds

Reactions of gaseous SF3 + ions with furan, thiophene, pyrrole, and several of their alkyl derivatives were performed via MS2 experiments and found to occur readily both by electron abstraction and F+ transfer. Then, by performing MS3 experiments, the F+ transfer products - the protonated monofluorinated molecules - were mass-selected and deprotonated by a second reaction with a stronger base. 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Mass Spectrometric Quantitation Of Chiral Drugs By The Kinetic Method

A novel mass spectrometric method for rapid, accurate (2-4% ee) quantitation of chiral drugs is described. Copper(II)-bound complexes of seven model drugs (atenolol, DOPA, ephedrine, pseudoephedrine, isoproterenol, norepinephrine, propranolol) with chiral reference compounds (L-amino acids) are generated by electrospray ionization mass spectrometry. The trimeric complex ions (three chiral ligands-one of the analyte and two of the reference compound) are collisionally activated, and they undergo dissociation by competitive loss of either the neutral reference or the neutral drug molecule. The ratio of the two competitive dissociation rates, viz. the product ion branching ratio, is related via the kinetic method to the enantiomeric composition of the drug mixture. A two-point calibration curve, derived from the kinetic method, allows rapid quantitation of enantiomeric excess of drug mixtures. The chiral sensitivity of the method is such as to allow determination of mixtures with a few percent enantiomeric contamination.73816921698Stinson, S.C., (2000) Chem. Eng. News, 78, p. 55McLafferty, F.W., Fridriksson, E.K., Horn, D.M., Lewis, M.A., Zubarev, R.A., (1999) Science, 284, p. 1289Menges, R.A., Armstrong, D.W., (1991) ACS Symposium Series 471, p. 67. , Chiral Separations by Liquid ChromatographyAhuja, S., Ed.American Chemical Society: Washington, DCNikolaev, E.N., Denisov, E.V., Nikolaeva, M.I., Futrell, J.H., Rakov, V.S., Winkler, F.J., (1998) Adv. Mass Spectrom., 14, p. 279Nikolaev, E.N., Denisov, E.V., Rakov, V.S., Futrell, J.H., (1999) Int. J. Mass Spectrom., 183, p. 357Sawada, M., (1997) Mass Spectrom. Rev., 16, p. 73Sawada, M., Takai, Y., Yamada, H., Hirayama, S., Kaneda, T., Tanaka, T., Kamada, K., Naemura, K., (1995) J. Am. Chem. Soc., 117, p. 7726Pocsfalvi, G., Liptak, M., Huszthy, P., Bradshaw, J.S., Izatt, R.M., Vekey, K., (1996) Anal. Chem., 68, p. 792Sawada, M., Takai, Y., Yamada, H., Nishida, J., Kaneda, T., Arakawa, R., Okamoto, M., Naemura, K., (1998) J. Chem. Soc., Perkin Trans. 2, 3, p. 701So, M.P., Wan, T.S.M., Chan, T.W.D., (2000) Rapid Commun. Mass Spectrom., 14, p. 692Chu, I.H., Dearden, D.V., Bradshaw, J.S., Huszthy, P., Izatt, R.M., (1993) J. Am. Chem. Soc., 115, p. 4318Dearden, D.V., Dejsupa, C., Liang, Y.J., Bradshaw, J.S., Izatt, R.M., (1997) J. Am. Chem. Soc., 119, p. 353Ramirez, J., He, F., Lebrilla, C.B., (1998) J. Am. Chem. Soc., 120, p. 7387Smith, G., Leary, J.A., (1996) J. Am. Chem. Soc., 118, p. 3293Ho, Y.H., Squires, R.R., (1992) J. Am. Chem. Soc., 114, p. 10961Tabet, J.C., (1987) Tetrahedron, 43, p. 3413Shen, W.Y., Wong, P.S.H., Cooks, R.G., (1997) Rapid Commun. Mass Spectrom., 11, p. 71Vekey, K., Czira, G., (1997) Anal. Chem., 69, p. 1700Tao, W.A., Zhang, D., Wang, F., Thomas, P., Cooks, R.G., (1999) Anal. Chem., 71, p. 4427Tao, W.A., Zhang, D., Nikolaev, E.N., Cooks, R.G., (2000) J. Am. Chem. Soc., 122, p. 10598Tao, W.A., Wu, L., Cooks, R.G., (2000) Chem. Commun., p. 2023Guo, J., Wu, J., Siuzdak, G., Finn, M.G., (1999) Angew. Chem., Int. Ed., 38, p. 1755Liang, Y.J., Bradshaw, J.S., Izatt, R.M., Pope, R.M., Dearden, D.V., (1999) Int. J. Mass Spectrom., 187, p. 977Grigorean, G., Ramirez, J., Ahn, S.H., Lebrilla, C.B., (2000) Anal. Chem., 72, p. 4275Cooks, R.G., Rockwood, A.L., (1991) Rapid Commun. Mass Spectrom., 5, p. 93Cooks, R.G., Wong, P.S.H., (1998) Acc. Chem. Res., 31, p. 379Cooks, R.G., Patrick, J.S., Kotiaho, T., McLuckey, S.A., (1994) Mass Spectrom. Rev., 13, p. 287Nemirovskiy, O.V., Gross, M.L., (2000) J. Am. Soc. Mass Spectrom., 11, p. 770Armentrout, P.B., (2000) J. Am. Soc. Mass Spectrom., 11, p. 371Kagan, H.B., Fiaud, J.C., (1988) Top. Stereochem., 18, p. 249Filippi, A., Giardini, A., Piccirillo, S., Speranza, M., (2000) Int. J. Mass Spectrom., 198, p. 137Tao, W.A., Cooks, R.G., (2001) Angew. Chem., Int. Ed., 40, p. 757Vedejs, E., Chen, X., (1997) J. Am. Chem. Soc., 119, p. 2584Eames, J., (2000) Angew. Chem., Int. Ed., 39, p. 885Salem, L., Chapuisat, X., Segal, G., Hiberty, P.C., Minot, C., Leforrestier, C., Sautet, P., (1987) J. Am. Chem. Soc., 109, p. 288

The Generation, Stability, Dissociation And Ion/molecule Chemistry Of Sulfinyl Cations In The Gas Phase

Sulfinyl cations [R-S+=O (R = CH3, Ph, Cl, CH 3O and C2H5O)] have been demonstrated by MO calculations in conjunction with pentaquadrupole multidimensional (2D and 3D) MS2 and MS3 mass spectrometric experiments to be stable and easily accessible gas phase species, and their dissociation and ion/molecule chemistry have been studied. Potential energy surface diagrams indicate that the sulfoxides (CH3)2S=O, Ph2S=O, Cl 2S=O, (CH3O)2S=O and (C2H 5O)2S=O do not undergo rearrangement upon dissociative ionization, yielding the corresponding sulfinyl cations as primary fragments. Ph(CH3)S=O+., on the other hand, is predicted to isomerize to CH3-S-O-Ph+. via a four-membered ring transition state, yielding upon further CH3 . loss the isomeric ion S=O+-Ph. The sulfinyl cations were found by ab initio calculations to be much more stable than their S=O+-R isomers, hence isomerization via [1,2-R] shifts is not expected. Direct cleavage of the R-SO+ bonds and/or processes that are preceded by isomerization dominate the low-energy collision dissociation chemistry of the sulfinyl cations, thus providing limited structural information. On the other hand, a general and structurally diagnostic ion/molecule reaction with 2-methyl-1,3-dioxolane occurs for all the sulfinyl cations yielding abundant net oxirane (C2H 4O) addition products. The reaction probably occurs via a transketalization-like mechanism that leads to cyclic 2-thia-1,3-dioxolanylium ions. This reactivity parallels that of several acylium (R-C+=O) and thioacylium ions (R-C+=S), and is not shared by the isomeric ions SO+-Ph and CH2=S+-OH. 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The Kinetic Method As A Structural Diagnostic Tool: Ionized α-diketones As Loosely One-electron Bonded Diacylium Ion Dimers

The kinetic method is used to corroborate the description of ground state ionized α-diketones as loosely electron-bonded acylium ion dimers: R 1-C=O+ - e- - +O=C-R2. The abundance ratio of both the acylium ion fragments R1CO + and R2CO+ (summed to those of their respective secondary fragments) formed upon low energy (5 eV) collision-induced dissociation of several ionized α-diketones is found to correlate linearly with the ionization energies (IEs) of the corresponding R 1CO• and R2CO• free radicals as predicted by density functional theory calculations at the B3LYP/6-311++G(d,p) level. However, when these abundances are taken from 70 eV electron ionization mass spectra, lower and sometimes inverted ratios (2,3-pentanedione and 2,3-hexanedione) are observed. Inverted ratios are also observed via charge-exchange mass spectrometry/mass spectrometry (MS/MS) experiments for ionized 2,3-pentanodione formed with relatively high internal energies. Ionized α-diketones are found to display an effective temperature of 1705 K, which indicates an intermediate loosely-bonded nature. B3LYP/6-311++G(d,p) optimized geometries and charge and spin densities also corroborate the description of ground state ionized α-diketones as loosely electron-bonded diacylium ion dimers.94295304Cooks, R.G., Kruger, T.L., Intrinsic basicity determination using metastable ions (1977) J. Am. Chem. Soc., 99, p. 1279Cooks, R.G., Patrick, J.S., Kotiaho, T., McLuckey, S.A., Thermochemical determinations by the kinetic method (1994) Mass Spectrom. Rev., 13, p. 287Cooks, R.G., Wong, P.S.H., Kinetic method of making thermochemical determinations: Advances and applications (1998) Acc. Chem. Res., 31, p. 379Yang, S.S., Chen, G.D., Ma, S.G., Cooks, R.G., Gozzo, F.C., Eberlin, M.N., Relative carbonyl isocyanate cation [OCNCO](+) affinities of pyridines determined by the kinetic method using multiple-stage (MS(3)) mass-spectrometry (1995) J. 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Mass Spectrom., 9, p. 1141Chen, G.D., Ma, S.G., Cooks, R.G., Bronstein, H.E., Best, M.D., Scott, L.T., Electron affinities and C-60 anion clusters of certain bowl-shaped polycyclic aromatic hydrocarbons (1997) J. Mass Spectrom., 32, p. 1305Chen, G.D., Cooks, R.G., Estimation of ionization energies of polycyclic aromatic hydrocarbons using the kinetic method (1997) J. Mass Spectrom., 32, p. 333Eberlin, M.N., Kotiaho, T., Shay, B.J., Yang, S.S., Cooks, R.G., Gas-phase Cl+ affinities of pyridines determined by the kinetic method using multiple-stage [MS(3)] mass-spectrometry (1994) J. Am. Chem. Soc., 116, p. 2457Ma, S.G., Wong, P., Cooks, R.G., Gozzo, F.C., Eberlin, M.N., Stereoelectronic effects in phosphorus dichloride cation pyridine complexes (1997) Int. J. Mass Spectrom. Ion Process, 163, p. 89Yang, S.S., Wong, P., Ma, S.G., Cooks, R.G., SiCl3 + and SiCl+ affinities for pyridines determined by using the kinetic method with multiple stage mass spectrometry: Agostic effects in the gas phase (1996) J. Am. Soc. Mass Spectrom., 7, p. 198Wang, F., Ma, S., Wong, P., Cooks, R.G., Gozzo, F.C., Eberlin, M.N., Gas phase agostic bonding in pyridine SiFn + (n = 1, 3) cluster ions investigated by the kinetic method (1998) Int. J. Mass Spectrom. Ion Proc., 180, p. 195Jarrold, M.F., Bower, J.E., Collision-induced dissociation of metal cluster ions - Bare aluminum clusters, Al+ (n = 3-26) (1987) J. Chem. Phys., 86, p. 3876Grese, R.P., Cerny, R.L., Gross, M.L., Senge, M., Determination of structure and properties of modified chlorophylls by using fast atom bombardment combined with tandem mass-spectrometry (1990) J. Am. Soc. 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Novel [3 + 2] 1,3-cycloaddition Of The Ionized Carbonyl Ylide +ch2och2· With Carbonyl Compounds In The Gas Phase

For the first time [3 + 2] 1,3-cycloaddition of an ionized carbonyl ylide has been observed in gas phase ion-molecule reactions of +CH2OCH2· (1) with several carbonyl compounds. The reaction, which competes with electrophilic addition that leads to net CH2·+ transfer, occurs across the C=O double bond of acetaldehyde and several acyclic ketones yielding ionized 4,4-dialkyl-1,3-dioxolanes as unstable cycloadducts. Rapid n of the nascent cycloadducts by loss of a 4-alkyl substituent as a radical leads to the observed products, that is cyclic 4-alkyl-1,3-dioxolanylium ions. Cycloaddition of 1 with cyclic ketones yields bicyclic spiro adducts, which also undergo rapid dissociation. Cyclobutanone yields ionized 1,3-dioxaspiro[4,3]octane, which dissociates exclusively by neutral ethene loss to ionized 4-methylene-1,3-dioxolane. Ionized 1,3-dioxaspiro[4,4]nonane is formed in reactions with cyclopentanone, and its rapid dissociation by loss of C3H6 and C2H5· yields the ionized 4-methylene-1,3-dioxolanylium and the 4-ethenyl-1,3-dioxolanylium product ions, respectively. A systematic study of this novel reaction and characterization of the product ions carried out via pentaquadrupole (QqQqQ) multiple stage (MS2 and MS3) mass spectrometric experiments provide experimental evidence for the cycloaddition mechanism. The dissociation chemistry observed for the cycloaddition products correlate well with their proposed structures and was compared to that of both isomeric and reference ions. 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Multiple Stage Pentaquadrupole Mass Spectrometry For Generation And Characterization Of Gas-phase Ionic Species. The Case Of The Pyc2h5/(+·) Isomers

Eleven isomers with the PyC2H5/(+·) composition, which include three conventional (1-3) and eight distonic radical cations (4-11), have been generated and in most cases successfully characterized in the gas phase via tandem-in-space multiple-stage pentaquadrupole MS2 and MS3 experiments. The three conventional radical cations, that is, the ionized ethylpyridines C2H5-C5H4N(+·) (1-3), were generated via direct 70-eV electron ionization of the neutrals, whereas sequences of chemical ionization and collision-induced dissociation (CID) or mass-selected ion-molecule reactions were used to generate the distonic ions H2C(·)-C5H4N+-CH3 (4-6), CH3- C5H4N+-CH2/(·) (7 9), CH5N5 +-CH2CH2/(·) (10), and C5H5N+- CH(·)-CH3 (11). Unique features of the low-energy (15-eV) CID and ion- molecule reaction chemistry with the diradical oxygen molecule of the isomers were used for their structural characterization. All the ion molecule reaction products of a mass-selected ion, each associated with its corresponding CID fragments, were collected in a single three-dimensional mass spectrum, Ab initio calculations at the ROMP2/6-31G(d, p)//6-31G(d, p) + ZPE level of theory were performed to estimate the energetics involved in interconversions within the PyC2H5/(+·) system, which provided theoretical support for facile 4 ⇆ 7 interconversion evidenced in both CID and ion- molecule reaction experiments. The ab initio spin densities for the α- distonic ions 4-9 and 11 were found to be largely on the methylene or methyne formal radical sites, which thus ruled out substantial odd-spin delocalization throughout the neighboring pyridine ring. However, only 8 and 9 (and 10) react extensively with oxygen by radical coupling, hence high spin densities on the radical site of the distonic ions do not necessarily lead to radical coupling reaction with oxygen. 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