M. George

Sacred Heart College

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Michael L. Gross

Washington University in St. Louis

Putcha Venkateswarlu

Andhra University

R. Srinivas

Michigan State University

John Holmes

University of Sheffield

G. Chakrapani

Atomic Minerals Directorate for Exploration and Research

Daryl Giblin

Washington University in St. Louis

D. V. Ramana

Vignan's Foundation for Science, Technology & Research

Jose Tharun

Utrecht University

N. Sundaram

Alagappa University

Amal Cherian Kathalikkattil

Trinity College Dublin

Cooperative Institutions

Pusan National University

Indian Institute of Chemical Technology

Alabama Agricultural and Mechanical University

Sacred Heart College

University of Nebraska–Lincoln

University of Nebraska Medical Center

Washington University in St. Louis

Indian Institute of Science Bangalore

Government of the Republic of Korea

University of Hyderabad

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Spectrophotometric assay of mefenamic acid in tablets using 1,4-dioxane as solvent for extraction

Indian Journal of Pharmaceutical Sciences (2010)

M. George JT Moolayil K.B. Jose VS Sebastian

A spectrophotometric method of assay of mefenamic acid in tablets involving, dissolving the tablet powder in 1,4-dioxane and measuring the absorbance at 353.2 nm. The concentration of mefenamic acid is determined using the previously prepared calibration curve using standard solution of mefenamic acid in dioxane. The method was tested by assay of six different commercial tablets containing mefenamic acid.

Mefenamic acid

Absorbance

10.4103/0250-474x.73928

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Citations (3)

McLafferty‐type rearrangement of protonated N‐[nicotinoyl]phenylethyl amines and consequent elimination of styrene

Rapid Communications in Mass Spectrometry (2015)

Justin Paulose Revi P. Achuthan M. George Purna A. Chander R. Srinivas

Rationale McLafferty rearrangements occur in radical cations of molecules containing a carbonyl group and a γ hydrogen atom but are not common in the [M+H] + ions of carbonyl compounds. We propose to investigate the collision‐induced dissociation (CID) of the [M+H] + ions of nicotinoyl and picolinoyl amides of 1‐ and 2‐phenylethylamines to explore the possibility of McLafferty‐type rearrangement. Methods The compounds for study were synthesized by the reaction of methyl nicotinate or methyl picolinate with 1‐ and 2‐phenylethylamines. The CID mass spectra of electrospray ionization (ESI)‐generated protonated molecules were obtained using a QSTAR XL quadrupole time‐of‐flight (QTOF) mass spectrometer, and density functional theory (DFT) calculations using the B3LYP method were employed to elucidate the fragmentation mechanisms. The total electronic and thermal energies of intermediate transition states (TSs) and product ions are reported relative to those of the [M+H] + ions. Results CID of the [M+H] + ions of N ‐[nicotinoyl]‐2‐phenylethylamine (1) yielded product ions of m/z 105 (1‐phenylethyl cation) and 123 ([M+H–styrene] + cation). The competitive formation of the ions of m/z 123 and 105 is proposed to involve a McLafferty‐type rearrangement. Similarly, the [M+H] + ions of the isomeric compound 2 and the N ‐[picolinoyl] phenylethyl amines (3 and 4) dissociate to yield ions of m/z 123 and 105. Conclusions A molecule of styrene was eliminated from the ESI‐generated [M+H] + ions of N ‐[nicotinoyl]phenylethylamines and the isomeric N ‐[picolinoyl]phenylethylamines, through a mechanism involving a McLafferty‐type 1,5‐H shift. The transition state energy for the 1,5‐H shift is less for the amides of 1‐phenylethylamine than for the amides of 2‐phenylethylamine. The process occurs as a charge remote process and the presence of the pyridine ring is essential for the process. Copyright © 2015 John Wiley & Sons, Ltd.

Fragmentation

Polyatomic ion

10.1002/rcm.7104

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Citations (2)

Improving the Sensitivity of FAB Tandem Mass Spectrometry for PAH-DNA Adducts

Polycyclic aromatic compounds (1994)

Joelle M. Y. Wellemans M. George Ronald L. Cerny Michael L. Gross

Abstract The mass spectrometric detection limits for guanine, adenine, and an adeninddimethylbenthracene adduct were greatly improved by converting the materials to pentafluorobenzyl derivatives, as well as by doing coaxial continuous flow-FAB (coaxial cf-Fast Atom Bombardment). The lowest detection limit (approximately 10 pg) was achieved when the derivatized sample was introduced by coaxial cf-FAB and the determination was by fill-scan mass spectrometry. The lowest detection limit achieved by tandem mass spectrometry was 50 pg obtained after derivatization, coaxial cf-FAB introduction and detection with an extended mass range array. Key Words: Tandem MSarray detectorPAH-DNA adductscoaxial cf-FABderivatizationdetection limit.

Coaxial

10.1080/10406639408031173

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Citations (1)

2-Nitrophenyl aryl sulfides undergo both intramolecular and electrospray-induced intermolecular oxidation of sulfur: An experimental and theoretical case study

International Journal of Mass Spectrometry (2009)

Joseph T. Moolayil M. George Daryl Giblin Michael L. Gross

Sulfoxide

10.1016/j.ijms.2009.04.003

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Citations (7)

Transient excited singlet state absorption in the laser dye proportional-NPO

AIP Conf. Proc.; (United States) (1987)

P. Venkateswarlu M. George Y.V. Chalapati Rao H. Jagannath G. Chakrapani

Excited single state absorption of the laser dye proportional-NPO solution in toluene recorded in the region 4460--6260 A shows nine submaxima and four shoulders whose origin can be traced to transitions from different vibrational levels of the lowest excited singlet state S/sub 1/ to those of two other upper singlet electronic states labeled S/sub 3/ and S/sub 4/.

Singlet fission

Source

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The Use of Tandem Mass Spectrometry for the Structure Determination of Adducts Formed Between DNA and Dibenzo[a,l]pyrene

Polycyclic aromatic compounds (1994)

Ronald L. Cerny Joelle M. Y. Wellemans M. George Michael L. Gross

Abstract Tandem mass spectrometry was used in the structure determinations of adducts formed between nucleosides and the potent carcinogen dibenzo[a,l]pyrene. Adducts expected to arise from both the one-electron oxidation mechanism and by the diol epoxide mechanism were studied. Structural isomers of the adducts can be distinguished by the fragment ions observed in their respective collisionally activated decomposition (CAD) spectra. Key Words: mass spectrometryFABMS/MSPAH-DNA adducts

Tandem

10.1080/10406639408031187

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Citations (4)

Structure Elucidation of the Adducts Formed by Fjord-Region Dibenzo[a,l]pyrene 11,12-Dihydrodiol 13,14-Epoxides and Deoxyadenosine

Chemical Research in Toxicology (1999)

Kaiming Li M. George Michael L. Gross Albrecht Seidel Andreas Luch

Model adducts to be used in the identification of biologically formed adducts were synthesized by reaction of fjord-region dibenzo[a,l]pyrene 11,12-dihydrodiol 13,14-epoxides (DB[a,l]PDE) and deoxyadenosine (dA). The (±)-anti-DB[a,l]PDE was reacted with dA in dimethylformamide at 100 °C for 30 min to give four DB[a,l]PDE-14-N6dA adducts: (−)-anti-trans (26%), (+)-anti-trans (26%), (−)-anti-cis (17%), and (+)-anti-cis (17%). The (±)-syn-DB[a,l]PDE was reacted with dA under the same conditions to yield four DB[a,l]PDE-14-N6dA adducts and one N7Ade adduct: (+)-syn-cis (19%), (+)-syn-trans (13%), (−)-syn-cis (19%), (−)-syn-trans (13%), and (±)-syn-DB[a,l]PDE-14-N7Ade (22%). The structures of the eight stereoisomers of DB[a,l]PDE-14-N6dA were unequivocally assigned by reacting optically pure (−)-anti-DB[a,l]PDE and (+)-syn-DB[a,l]PDE with dA and by a combination of NMR, circular dichroism, and fast atom bombardment mass spectrometry. Reactions at 100 °C yielded mainly the trans-opened adducts at the benzylic C-14 position for both (±)-anti-DB[a,l]PDE and (−)-anti-DB[a,l]PDE, whereas (±)-syn-DB[a,l]PDE and (+)-syn-DB[a,l]PDE afforded mainly cis-opened adducts. At room temperature, however, only trans-opened adducts were obtained from (±)-anti-DB[a,l]PDE and only cis-opened adducts from (±)-syn-DB[a,l]PDE. Steric hindrance created by the fjord region may be an important factor for the stereoselectivity observed at room temperature.

Deoxyadenosine

10.1021/tx980197x

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Citations (6)

Investigation of Group Migration in the Fragmentation of Bistrimethylsilyl Ethers of Diols Separated by Rigid Groups

Journal of Mass Spectrometry (1997)

Jaeman Byun Michael L. Gross M. George David M. Parees A.Z. Kamzelski

Two fragmentations of (CH3)3SiO-CR2-X-CR2-OSi(CH3)3, where X is a rigid group such as a triple bond or an aromatic ring, are losses of a methyl or R group (where R is H or alkyl). The metastable-ion dissociations of [M-R]+ and [M-CH3]+ ions include the rearrangement of a trimethylsilyl (TMS) cation and a (CH3)2Si=O neutral species through an ion–neutral complex. On the basis of tandem mass spectrometry (MS/MS), exact mass measurement and isotopic labeling experiments, it has been established that the two trimethylsilyloxy groups in the TMS ethers interact across a wide range of distances via an ion–neutral complex. The migration of a TMS cation occurs when the group that is bound to carbon is expelled as a radical by an oxygen-directed cleavage to give a trimethylsilylated oxonium ion. If, on the other hand, a methyl radical is lost from the silicon atom, then (CH3)2Si=O migrates. The mobilities of the TMS cation and the neutral (CH3)2Si=O are governed by the capability of the rigid group to delocalize charge. © 1997 by John Wiley & Sons, Ltd.

Oxonium ion

Trimethylsilyl

Fragmentation

Carbenium ion

Radical ion

Methyl group

Polyatomic ion

10.1002/(sici)1096-9888(199701)32:1<71::aid-jms452>3.3.co;2-0

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Gas-phase nazarov cyclization of protonated 2-methoxy and 2-hydroxychalcone: An example of intramolecular proton-transport catalysis

Journal of the American Society for Mass Spectrometry (2009)

M. George Valarkottu S. Sebastian P. Nagi Reddy R. Srinivas Daryl Giblin

Upon CA, ESI generated [M + H](+) ions of chalcone (benzalacetophenone) and 3-phenyl-indanone both undergo losses of H(2)O, CO, and the elements of benzene. CA of the [M + H](+) ions of 2-methoxy and 2-hydroxychalcone, however, prompts instead a dominant loss of ketene. In addition, CA of the [M + H](+) ions of 2-methoxy-beta-methylchalcone produces an analogous loss of methylketene instead. Furthermore, the [M + D](+) ion of 2-methoxychalcone upon CA eliminates only unlabeled ketene, and the resultant product, the [M + D - ketene](+) ion, yields only the benzyl-d(1) cation upon CA. We propose that the 2-methoxy and 2-hydroxy (ortho) substituents facilitate a Nazarov cyclization to the corresponding protonated 3-aryl-indanones by mediating a critical proton transfer. The resultant protonated indanones then undergo a second proton transport catalysis facilitated by the same ortho substituents producing intermediates that eliminate ketene to yield 2-methoxy- or 2-hydroxyphenyl-phenyl-methylcarbocations, respectively. The basicity of the ortho substituent is important; for example, replacement of the ortho function with a chloro substituent does not provide an efficient catalyst for the proton transports. The Nazarov cyclization must compete with an alternate cyclization, driven by the protonated carbonyl group of the chalcone that results in losses of H(2)O and CO. The assisted proton transfer mediated by the ortho substituent shifts the competition in favor of the Nazarov cyclization. The proposed mechanisms for cyclization and fragmentation are supported by high-mass resolving power data, tandem mass spectra, deuterium labeling, and molecular orbital calculations.

Chalcone

10.1016/j.jasms.2008.12.017

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Citations (25)

Photoacoustic spectrum (17,750-18,960 cm–1) of Br2

Annual Meeting Optical Society of America (1989)

Putcha Venkateswarlu G. Chakrapani M. George M. Henry

Kumar et al. 1 recorded the photoacoustic spectrum (16,100-17,400 cm –1 ) of Br 2 using a flashlamp pumped dye laser. We recorded here the spectrum in the 17,840–18,900-cm –1 region using an excimer laser pumped tunable dye laser and a photoacoustic spectrometer recently assembled. 2 Optogalvanic spectrum of Ne is used for wavelength standards. Partial pressure of Br 2 is ~250 Torr and that of air is 510 Torr. This spectrum involves the transition X 1 Σ g + → B 3 I I ( 0 u + ) with (18 ≤ V ≤ 49) and (0 ≤ V" ≤ 5). Nonradiative vibrational-rotational energy transfers in B and X states are responsible for the photoacoustic spectrum. High values of υ" are reached by fluorescence from the B state and they go to lower levels only by nonradiative energy transfers as Br 2 is homonuclear. The result is that V" = 4 and 5 are well populated at room temperature although the corresponding Boltz-mann factor for these levels is not high.

10.1364/oam.1989.tus4

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