1,721,040 research outputs found
Mass Spectrometric Quantitation Of Chiral Drugs By The Kinetic Method
No full textA 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
Sulfur Trifluoride Cation (sf3 +) Affinities Of Pyridines Determined By The Kinetic Method: Stereoelectronic Effects In The Gas Phase
No full textIon/molecule reactions performed by pentaquadrupole mass spectrometry are used to generate cluster ions in which neutral pyridines are bound to the polyatomic cation SF3 +. The dimeric ions Py1SF3 +Py2, where Py1 and Py2 represent substituted pyridines, are shown to have loosely bound structures by collision-induced dissociation (MS3) experiments and by semiempirical AM1 and ab initio RHF/6-31G(d, p) molecular orbital calculations. In the case of dimers comprised of meta- and/or para- substituted pyridines (unhindered pyridines), there is an excellent linear correlation between the logarithm of the fragment ion abundance ratio In{[Py1(SF3 +)]/[Py(SF3 +)]} and the proton affinities (PA) of the constituent pyridines. Semiempirical calculations are used to estimate the SF3 + affinities of pyridines which are found to be in the range of 25-31 kcal/mol. The SF3 + affinities show an excellent linear correlation with the proton affinities of the pyridines, and the relationship SF3 + affinity (kcal/mol) = 0.73PA - 135.8 between the two affinities is derived. The effective temperature of the dimeric ions is determined to be 595 ± 69 K, which is in good agreement with values of around 600 K obtained experimentally in studies on many other systems activated under similar conditions. Ortho-substituted pyridines show lower than expected affinities due to stereoelectronic effects that decrease the cation affinities. Gas- phase stereoelectronic parameters (S(k)) are measured from the deviation from the PA correlation and are ordered as 2-MePy (-1.09) < 2,6-diMePy (-1.11) < 2-EtPy (-1.91) < 2,3-diMePy (-2.15) < 2,5-diMePy (-2.25) < 2,4-diMePy (- 2.40). Overall, the steric effects are larger than those in the corresponding Cl+-bound dimers but smaller than those in the bulky [OCNCO+] system. Calculations show evidence for agostic bonding that offsets the steric effects in some cases. The eclipsed conformation of 2-methylpyridine/SF3 + adduct is found to be more stable than the staggered form by 0.8 kcal/mol, due to auxiliary agostic bonding between the hydrogen of the ortho methyl substituent and the sulfur atom. Calculations on atomic charge distribution reveal that the positive charge is mainly on the sulfur atom (+ 1.99) and the charge on the bonding hydrogen S-H-C (+0.07) is considerably lower than that on the other two methyl hydrogens (+0.14), which appears to be a good indication of agostic binding. The most stable form of the 2- ethylpyridine/SF3 + adduct is found when the N-C1-C(α)-C(β) dihedral angle is approximately 60°, where the ethyl hydrogen is directed toward the SF3 group via an interesting six-membered ring alignment. The experiments show a remarkably small steric effect in 2,6-dimethylpyridine, probably due to strong agostic bonding enhanced by the buttressing effect that shortens the S-H distance. In addition, the face-to-face interactions of the F atoms and the H atoms further stabilize this form.816875Bowers, M.T., (1979) Gas Phase Ion Chemistry, 1-3. , Academic: New YorkFutrell, J.H., (1986) Gaseous Ion Chemistry and Mass Spectrometry, , Wiley: New YorkLias, S.G., Ausloos, P., (1975) Ion-molecule Reactions, Their Role in Radiation Chemistry, , American Chemical Society: Washington, DCFranklin, J.L., (1972) Ion-molecule Reactions, , Plenum: New YorkHarrison, A.G., (1983) Chemical Ionization Mass Spectrometry, , CRC: Boca Raton, FLCooks, R.G., Patrick, J.S., Kotiaho, T., McLuckey, S.A., (1994) Mass Spectrom. Rev., 13, p. 287McLuckey, S.A., Cameron, D., Cooks, R.G., (1981) J. Am. Chem. Soc., 103, p. 1313Eberlin, M.N., Kotiaho, T., Shay, B.J., Yang, S.S., Cooks, R.G., (1994) J. Am. Chem. 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Single-Biomolecule Kinetics: The Art of Studying a Single Enzyme
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The Proton-bound Dimer Of Acetone [2]
No full text[No abstract available]401127128Derrick, P.J., (1982) Mass Spectrom. Rev., 2, p. 285Nourse, B.D., Cooks, R.G., (1991) Int. J. Mass Spectrom. Ion Processes, 106, p. 249Dang, T.T., Motell, E.L., Travers, M.J., Clifford, E.P., Ellison, G.B., DePuy, C.H., Bierbaum, V.M., (1993) Int. J. Mass Spectrom. Ion Processes, 123, p. 171O'Hair, R.A.J., Gronert, S., Williams, T.D., (1994) Org. Mass Spectrom., 29, p. 151Norman, K., McMahon, T.B., (1999) Int. J. Mass Spectrom., 182-183, p. 381Schröder, D., Semialjac, M., Schwarz, H., (2004) Int. J. Mass Spectrom., 223, p. 103Gozzo, F.C., Eberlin, M.N., (2001) J. Mass Spectrom., 36, p. 1140Eberlin, M.N., (1997) Mass Spectrom. Rev., 16, p. 113Juliano, V.F., Gozzo, F.C., Eberlin, M.N., Rascheres, C., Do Lago, C.L., (1996) Anal. Chem., 68, p. 1328Santos, L.S., Pavam, C.H., Almeida, W.P., Coelho, F., Eberlin, M.N., (2004) Angew. Chem. Int. Ed., 43, p. 4330Sabino, A.A., Machado, A.H.L., Correia, C.R.D., Eberlin, M.N., (2004) Angew. Chem. Int. Ed., 43, p. 2514Eberlin, M.N., Kotiaho, T., Shay, B.J., Yang, S.S., Cooks, R.G., (1994) J. Am. Chem. Soc., 116, p. 2457Yang, S.S., Wong, P., Ma, S.G., Cooks, R.G., (1996) J. Am. Soc. Mass Spectrom., 7, p. 198Meurer, E.C., Gozzo, F.C., Augusti, R., Eberlin, M.N., (2003) Eur. J. Mass Spectrom., 9, p. 295Denault, J.W., Wang, F., Cooks, R.G., Gozzo, F.C., Eberlin, M.N., (2000) J. Phys. Chem. A, 104, pp. 11 290Chen, G., Cooks, R.G., Corpuz, E., Scott, L.T., (1996) J. Am. Soc. Mass Spectrom., 7, p. 61
Chemical and Biological Dynamics Using Droplet-Based Microfluidics
No full text Recent years have witnessed an increased use of droplet-based microfluidic techniques in a wide variety of chemical and biological assays. Nevertheless, obtaining dynamic data from these platforms has remained challenging, as this often requires reading the same droplets (possibly thousands of them) multiple times over a wide range of intervals (from milliseconds to hours). In this review, we introduce the elemental techniques for the formation and manipulation of microfluidic droplets, together with the most recent developments in these areas. We then discuss a wide range of analytical methods that have been successfully adapted for analyte detection in droplets. Finally, we highlight a diversity of studies where droplet-based microfluidic strategies have enabled the characterization of dynamic systems that would otherwise have remained unexplorable. </jats:p
Monolithic Phases for Ion Chromatography
No full text Monolithic media are continuing to increase in popularity in chromatographic applications, and the ongoing use of commercially available materials in ion chromatography (IC) has made monoliths a viable alternative to packed-bed columns for routine use. We discuss different strategies for the synthesis of polymeric and silica monoliths with ion-exchange functionality, such as direct incorporation of ion-exchange functionality during monolith preparation and different postpolymerization alterations such as grafting and coating. The formulations and strategies presented are focused on materials intended for use in IC. We also discuss strategies for materials characterization, with emphasis on nondestructive techniques for the characterization of monolith surface functionality, especially those with applicability to in situ analysis. Finally, we describe selected IC applications of polymeric and silica monoliths published from 2008 to 2010. </jats:p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fast Multidimensional (3d And 4d) Ms2 And Ms3 Scans In A High-transmission Pentaquadrupole Mass Spectrometer
No full textA high-transmission Extrel pentaquadrupole mass spectrometer was interfaced to an IBM-compatible microcomputer, and a variety of object-oriented programs in the Microsoft Windows operating system were developed to operate and to increase the versatility of the instrument A selective prescan procedure and the complete control of all three mass-scanning quadrupoles made possible very fast acquisition of several types of three- and four-dimensional MS2 and MS3 spectra, while the high transmission of the quadrupoles conferred excellent signal-to-noise levels to both MS2 and MS3 spectra. By performing an unrestricted third-order (MS3) experiment through scanning of the three mass-analyzer quadrupoles, an entire MS3 data domain was acquired, and the results were collected in the first 4D MS3 mass spectrum. Data projection and data extraction procedures were applied to the 4D spectrum, each of which yielded spectra that provide very specific analytical information. The applicabilities of this and several other multidimensional mass scans were further demonstrated, particularly toward the study of gas phase ion chemistry processes. A consecutive MS3 neutral gain/neutral loss scan was for the first time applied and proved to be very selective for the detection of acylium ions in the gas phase. The application of a 3D MS2 scan, applied in conjunction with the membrane introduction mass spectrometry technique, for fast and simultaneous qualitative, quantitative, and structural analyses of volatile organic compounds in water was also demonstrated.68813281334McLafferty, F.W., (1993) Org. Mass Spectrom., 28, p. 1403McLafferty, F.W., (1983) Tandem Mass Spectrometry, , Wiley: New YorkBusch, K.L., Glish, G.L., McLuckey, S.A., (1988) Mass Spectrometry/Mass Spectrometry: Techniques and Applications of Tandem Mass Spectrometry, , VCH: New YorkCooks, R.G., (1979) Collision Spectroscopy, , Plenum: New YorkCooks, R.G., Hoke II, S.H., Lammert, S.A., (1992) Int. 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Acta, 310, p. 281Extrel Mass Spectrometry (1992) Model C50 Mass Spectrometer-User Reference Manual, , Extrel Corp.: Pittsburgh, PAThe name "familial scan" has been chosen to describe the experiment since the relationship of all products and all parents to a particular intermediate ion is obtainedsee ref 2noteBudzikiewicz, H., Djerassi, C., Williams, D.H., (1967) Mass Spectrometry of Organic Compounds, , Holden-Day: San FrancisconoteGozzo, F.C., Eberlin, M.N., Unpublished resultsYost, R.A., Enke, C.G., (1986) Mass Spectrometry in Biomedical Research, , Gaskell, S. J., Ed.Wiley: New York, Chapter 8Eckenrode, B.A., Watson, J.T., Enke, C.G., Holland, J.F., (1988) Int. J. Mass Spectrom. Ion Processes, 83, p. 177Coutant, J.E., McLafferty, F.W., (1972) Int. J. Mass Spectrom. Ion Phys., 8, p. 23Lacey, M.J., MacDonald, C.G., (1978) Organic Mass Spectrom., 13, p. 284Lacey, M. J.MacDonald, C. G. In ref 1b, Chapter 16Warburton, G.A., Stradling, R.S., Mason, R.S., Farncombe, M., (1981) Org. 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Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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