M. Vairamani - Academia.edu (original) (raw)
Papers by M. Vairamani
International Journal of Biological Macromolecules
Chemischer Informationsdienst
Anal. Methods, 2016
Direct injection of alcoholic samples/broths into a RP-HPLC (with a PDA-UV detector) system to qu... more Direct injection of alcoholic samples/broths into a RP-HPLC (with a PDA-UV detector) system to quantify ethanol directly as a negative peak. The kind of peak pair depends on the ethanol concentration as described in the article.
International Journal of Biological Macromolecules, 2015
Scaffold based bone tissue engineering utilizes a variety of biopolymers in different combination... more Scaffold based bone tissue engineering utilizes a variety of biopolymers in different combinations aiming to deliver optimal properties required for bone regeneration. In the current study, we fabricated bio-composite scaffolds containing chitosan (CS), carboxymethylcellulose (CMC) with varied concentrations of mesoporous wollastonite (m-WS) particles by the freeze drying method. The CS/CMC/m-WS scaffolds were characterized by the SEM, EDS and FT-IR studies. Addition of m-WS particles had no effect on altering the porosity of the scaffolds. m-WS particles at 0.5% concentration in the CS/CMC scaffolds showed significant improvement in the bio-mineralization and protein adsorption properties. Addition of m-WS particles in the CS/CMC scaffolds significantly reduced their swelling and degradation properties. The CS/CMC/m-WS scaffolds also showed cyto-friendly nature to human osteoblastic cells. The osteogenic potential of CS/CMC/m-WS scaffolds was confirmed by calcium deposition and expression of an osteoblast specific microRNA, pre-mir-15b. Thus, the current investigations support the use of CS/CMC/m-WS scaffolds for bone tissue engineering applications.
Journal of the Chemical Society, Faraday Transactions, 1993
ABSTRACT
Rapid Communications in Mass Spectrometry, 2012
In chiral differentiation by mass spectrometry, use of a single reference that differentiates var... more In chiral differentiation by mass spectrometry, use of a single reference that differentiates various classes of compounds including drugs is ideal, but so far there are no such reports in the literature. We have successfully used iodo-substituted amino acids for the chiral differentiation of ten enantiomeric pairs of drugs. To achieve the chiral differentiation, the trimeric Cu complex ion consisting of two chiral reference molecules and an analyte molecule was generated under positive ion electrospray ionization (ESI) conditions and subsequently subjected for collision- induced dissociation (CID) experiments using an LCQ ion trap mass spectrometer. The spectra were recorded under identical experimental conditions for both the enantiomers, and were averages of 30 scans. Cooks' kinetic method and chiral recognition ratio method (CR method) were used to arrive at the R(chiral) /CR values, respectively. The R(chiral) or CR values of the studied drugs are higher for 3,5-diiodo-L-tyrosine as the reference, than for 4-iodo-L-phenylalanine, except for isoproterenol and atenolol. Both the references show the same selectivity (R- or S-selectivity) towards all the studied drugs. With 3,5-diiodo-L-tyrosine as the reference, an R(chiral) value of 12.75 is obtained for DOPA and this is the highest reported value in the literature till now. The suitability of the current method in measuring enantiomeric excess is also demonstrated for DOPA. The use of 4-iodo-L-phenylalanine or 3,5-diiodo-L-tyrosine as a chiral reference for the chiral differentiation of ten enantiomeric pairs of pharmaceutically important drugs has been demonstrated. The chiral differentiation of pregabalin, tenofovir and pramipexole is reported for the first time. This study shows that it is possible to develop a single chiral reference compound for the differentiation of a group of chiral drugs having some similarities.
Rapid Communications in Mass Spectrometry, 2013
The isomeric dialkyl alkylphosphonothiolates and dialkyl alkylphosphonothionates are listed as sc... more The isomeric dialkyl alkylphosphonothiolates and dialkyl alkylphosphonothionates are listed as scheduled chemicals of the Chemical Weapons Convention (CWC) implemented by the OPCW. The P-S and P-R bond connectivity has to be correctly identified for the verification of the CWC. The present study demonstrates successful identification of the target isomers by selective fragmentation under electron ionization (EI) or chemical ionization (CI) conditions. All the studied isomeric compounds (27 in total) were synthesized in our laboratory using established methods, then analyzed by EI and CI gas chromatography/mass spectrometry (GC/MS) using an Agilent 6890 gas chromatograph equipped with a HP-5MS capillary column and interfaced to a 5973 N mass-selective detector. The retention index (RI) values of all the compounds were calculated using Van den Dool's formula. GC/MS/MS and GC/HRMS experiments were also performed using a VG-Autospec (magnetic sector) and JEOL-AccuToF (time-of-flight) mass spectrometer, respectively. The EI mass spectra of all the compounds had an abundant molecular ion at m/z 182, except in the case of a few selected butyl-substituted compounds, where this ion was of low abundance. The EI fragmentation pathways include α-cleavage, McLafferty rearrangement, McLafferty + 1 rearrangement, O/S-alkyl radical loss, and an alkene loss with a hydrogen shift. The characteristic fragment ions and their relative abundances are significant in elucidating the alkyl group attached to the P/S/O-atoms as well as the P-S/P = S bond connectivity. The EI and CI mass spectra together with RI values enable unambiguous identification of all the studied isomeric compounds. The present study highlights the structural characterization of the isomeric phosphonothiolates and phosphonothionates based on their selective EI fragmentation. The assigned fragmentation pathway helps in the assignment of P-S and P-alkyl connectivity in phosphonothiolates and phosphonothionates, consequently the structure of the unknown compounds. The EI mass spectra (27 compounds) of isomeric compounds are immensely useful in the OPCW official proficiency tests and for off-site analysis.
The Indian journal of medical research, 2004
Beta haemolytic streptococci belonging to Lancefield group A, B, C and G cause a wide spectrum of... more Beta haemolytic streptococci belonging to Lancefield group A, B, C and G cause a wide spectrum of clinical diseases. Hence there is a need for rapid and accurate typing of these strains. The present study was undertaken to evaluate the use of intact cell matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for rapid discrimination between strains of beta haemolytic streptococci. Colonies of beta haemolytic streptococci were emulsified with chemical matrix on the sample slide, dried and analyzed by MALDI-TOF-MS. The reproducibility of results for all groups of beta haemolytic streptococci was good and spectra obtained for Lancefield group A, C and G streptococci showed discrimination between the groups on visual comparison. A finer difference in spectrum was observed among group A streptococci isolated from different locations at different periods of time. MALDI-TOF-MS may be a potential tool in discriminating between strains of beta haemolytic ...
Rapid Communications in Mass Spectrometry, 2005
ABSTRACT The gas-phase acidities (GA) of a series of dicarboxylic acids were estimated by applyin... more ABSTRACT The gas-phase acidities (GA) of a series of dicarboxylic acids were estimated by applying the extended kinetic method. Proton-bound heterodimeric anions [A−H+B−] of a series of dicarboxylic acids (A) and reference compounds (B) were generated under electrospray ionization conditions, and the dissociation of these cluster ions was examined using a triple-quadrupole mass spectrometer. The mass-selected proton-bound heterodimeric anions were fragmented to yield individual monomer anions as the only product ions, and the abundance ratios of these anions were used to estimate the GA values of the dicarboxylic acids. The experiment was performed over a range of collision energies in order to more accurately determine GA values and to estimate the differences in the entropy of deprotonation of the dicarboxylic acids and the reference compounds. The trends in GA values obtained for the dicarboxylic acids could imply cyclization of the structures via intramolecular hydrogen bonding. The lower homologues show higher GA values than the higher homologues. The GA order for lower homologues is comparable with that of their solution-phase pKa1 values. Copyright © 2005 John Wiley & Sons, Ltd.
Tetrahedron, 1998
cis,syn,cis-Triquinane diol 1, with its folded topology, hydrophobic posterior and inwardly direc... more cis,syn,cis-Triquinane diol 1, with its folded topology, hydrophobic posterior and inwardly directed endo,endo-hydroxy groups, readily enters into cyclooligomerization reaction with terephthaloyldichloride 4. As many as nine cyclic oligomers A-I, with macrocyclic ring size varying from 28- to 98-membered, have been isolated and characterized. The cyclic oligomers exhibit interesting spatial relationships through the relative orientation of methylene groups on the central
Special Paper 356: Catastrophic events and mass extinctions: impacts and beyond, 2002
Tetrahedron: Asymmetry, 2003
![Research paper thumbnail of Boron Trifluoride-Etherate Induced Rearrangement of Bicyclo[2.2.2]octenediones: An Efficient Synthesis of Bicyclo[3.2.1]octenediones](https://attachments.academia-assets.com/68415713/thumbnails/1.jpg)
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Synthetic Communications, 1980
... at 190°C in an evacuated sealed tube fOr,4 hrs. Dlels-Alder adduct a, mp 155OC (27%) and CL c... more ... at 190°C in an evacuated sealed tube fOr,4 hrs. Dlels-Alder adduct a, mp 155OC (27%) and CL crystalline product 20 which melts at l58OC (28.5$) The t NCL Communlca tion !io. 2458 843 Copyriat 0 1980 by Marcel Dekker, Inc. Page 2. AFZAL ET AL. a44 were Isolated. ...
Rapid Communications in Mass Spectrometry, 2004
The gas-phase coordination behavior of the [Cr(III)(Salen)]PF(6) complex at the free axial positi... more The gas-phase coordination behavior of the [Cr(III)(Salen)]PF(6) complex at the free axial positions has been studied in the presence of amines as ligands (propylamine and a series of diamines) under electrospray ionization conditions. The [Cr(III)(Salen)](+) complex formed stable five- and six-coordinated complex ions, [Cr(III)(Salen)(L)](+) and [Cr(III)(Salen)(L)(2)](+), respectively, where L = solvent molecule or amine. When diamines were used as ligands, abundant [Cr(III)(Salen)(L)](+) ions were observed in which two axial positions of the [Cr(III)(Salen)](+) species are occupied by the two amino groups of the diamine ligand. The relative abundances of ligated complex ions, fragment ions, and solvent adducts of fragment ions in the ESI mass spectra, were found to depend on the cone voltage used to record the spectrum. The ESI mass spectra of [Cr(III)(Salen)](+) in the presence of diamines as ligands, and experiments on ligand-pickup in the collision cell, clearly demonstrated that the [Cr(III)(Salen)(L)](+) complex ion is stable for 1,2-diaminoethane and 1,3-diaminopropane. The stability of [Cr(III)(Salen)(L)](+) ions gradually decreased from 1,4-diaminobutane to 1,6-diaminohexane, and then showed a slight increase for 1,7-diaminoheptane and 1,8-diaminooctane. The collision-induced dissociation spectra of [Cr(III)(Salen)(L)](+) ions support the above observations.
Rapid Communications in Mass Spectrometry, 2007
Diastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)-6-(N-carbomethoxyamino) 1,2-O-isopr... more Diastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)-6-(N-carbomethoxyamino) 1,2-O-isopropylidenecyclohex-4-ene-1,2,3-triol (1 and 2) and their O-acetyl derivatives (3 and 4), were studied using gas chromatography (GC) with electron ionization (EI) and chemical ionization (CI). The EI mass spectra of diastereomeric pairs show consistent differences in the relative abundances of characteristic ions. The EI fragmentation patterns are based on precursor/product ion spectra, high-resolution mass spectrometry (HRMS) and deuterium labelling. The CI spectra show differences from the EI spectra, and the isobutane/CI spectra are much simpler than the methane/CI spectra. The differences shown in the CI spectra are similar to those shown in the product ion spectra of [M+H](+) ions generated under electrospray ionization (ESI) conditions. Theoretical calculations are performed to understand the observed differences. The differences in the relative stabilities of molecular ions, or protonated molecules at different sites, can explain the observed differences in the spectra.
International Journal of Biological Macromolecules
Chemischer Informationsdienst
Anal. Methods, 2016
Direct injection of alcoholic samples/broths into a RP-HPLC (with a PDA-UV detector) system to qu... more Direct injection of alcoholic samples/broths into a RP-HPLC (with a PDA-UV detector) system to quantify ethanol directly as a negative peak. The kind of peak pair depends on the ethanol concentration as described in the article.
International Journal of Biological Macromolecules, 2015
Scaffold based bone tissue engineering utilizes a variety of biopolymers in different combination... more Scaffold based bone tissue engineering utilizes a variety of biopolymers in different combinations aiming to deliver optimal properties required for bone regeneration. In the current study, we fabricated bio-composite scaffolds containing chitosan (CS), carboxymethylcellulose (CMC) with varied concentrations of mesoporous wollastonite (m-WS) particles by the freeze drying method. The CS/CMC/m-WS scaffolds were characterized by the SEM, EDS and FT-IR studies. Addition of m-WS particles had no effect on altering the porosity of the scaffolds. m-WS particles at 0.5% concentration in the CS/CMC scaffolds showed significant improvement in the bio-mineralization and protein adsorption properties. Addition of m-WS particles in the CS/CMC scaffolds significantly reduced their swelling and degradation properties. The CS/CMC/m-WS scaffolds also showed cyto-friendly nature to human osteoblastic cells. The osteogenic potential of CS/CMC/m-WS scaffolds was confirmed by calcium deposition and expression of an osteoblast specific microRNA, pre-mir-15b. Thus, the current investigations support the use of CS/CMC/m-WS scaffolds for bone tissue engineering applications.
Journal of the Chemical Society, Faraday Transactions, 1993
ABSTRACT
Rapid Communications in Mass Spectrometry, 2012
In chiral differentiation by mass spectrometry, use of a single reference that differentiates var... more In chiral differentiation by mass spectrometry, use of a single reference that differentiates various classes of compounds including drugs is ideal, but so far there are no such reports in the literature. We have successfully used iodo-substituted amino acids for the chiral differentiation of ten enantiomeric pairs of drugs. To achieve the chiral differentiation, the trimeric Cu complex ion consisting of two chiral reference molecules and an analyte molecule was generated under positive ion electrospray ionization (ESI) conditions and subsequently subjected for collision- induced dissociation (CID) experiments using an LCQ ion trap mass spectrometer. The spectra were recorded under identical experimental conditions for both the enantiomers, and were averages of 30 scans. Cooks' kinetic method and chiral recognition ratio method (CR method) were used to arrive at the R(chiral) /CR values, respectively. The R(chiral) or CR values of the studied drugs are higher for 3,5-diiodo-L-tyrosine as the reference, than for 4-iodo-L-phenylalanine, except for isoproterenol and atenolol. Both the references show the same selectivity (R- or S-selectivity) towards all the studied drugs. With 3,5-diiodo-L-tyrosine as the reference, an R(chiral) value of 12.75 is obtained for DOPA and this is the highest reported value in the literature till now. The suitability of the current method in measuring enantiomeric excess is also demonstrated for DOPA. The use of 4-iodo-L-phenylalanine or 3,5-diiodo-L-tyrosine as a chiral reference for the chiral differentiation of ten enantiomeric pairs of pharmaceutically important drugs has been demonstrated. The chiral differentiation of pregabalin, tenofovir and pramipexole is reported for the first time. This study shows that it is possible to develop a single chiral reference compound for the differentiation of a group of chiral drugs having some similarities.
Rapid Communications in Mass Spectrometry, 2013
The isomeric dialkyl alkylphosphonothiolates and dialkyl alkylphosphonothionates are listed as sc... more The isomeric dialkyl alkylphosphonothiolates and dialkyl alkylphosphonothionates are listed as scheduled chemicals of the Chemical Weapons Convention (CWC) implemented by the OPCW. The P-S and P-R bond connectivity has to be correctly identified for the verification of the CWC. The present study demonstrates successful identification of the target isomers by selective fragmentation under electron ionization (EI) or chemical ionization (CI) conditions. All the studied isomeric compounds (27 in total) were synthesized in our laboratory using established methods, then analyzed by EI and CI gas chromatography/mass spectrometry (GC/MS) using an Agilent 6890 gas chromatograph equipped with a HP-5MS capillary column and interfaced to a 5973 N mass-selective detector. The retention index (RI) values of all the compounds were calculated using Van den Dool's formula. GC/MS/MS and GC/HRMS experiments were also performed using a VG-Autospec (magnetic sector) and JEOL-AccuToF (time-of-flight) mass spectrometer, respectively. The EI mass spectra of all the compounds had an abundant molecular ion at m/z 182, except in the case of a few selected butyl-substituted compounds, where this ion was of low abundance. The EI fragmentation pathways include α-cleavage, McLafferty rearrangement, McLafferty + 1 rearrangement, O/S-alkyl radical loss, and an alkene loss with a hydrogen shift. The characteristic fragment ions and their relative abundances are significant in elucidating the alkyl group attached to the P/S/O-atoms as well as the P-S/P = S bond connectivity. The EI and CI mass spectra together with RI values enable unambiguous identification of all the studied isomeric compounds. The present study highlights the structural characterization of the isomeric phosphonothiolates and phosphonothionates based on their selective EI fragmentation. The assigned fragmentation pathway helps in the assignment of P-S and P-alkyl connectivity in phosphonothiolates and phosphonothionates, consequently the structure of the unknown compounds. The EI mass spectra (27 compounds) of isomeric compounds are immensely useful in the OPCW official proficiency tests and for off-site analysis.
The Indian journal of medical research, 2004
Beta haemolytic streptococci belonging to Lancefield group A, B, C and G cause a wide spectrum of... more Beta haemolytic streptococci belonging to Lancefield group A, B, C and G cause a wide spectrum of clinical diseases. Hence there is a need for rapid and accurate typing of these strains. The present study was undertaken to evaluate the use of intact cell matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for rapid discrimination between strains of beta haemolytic streptococci. Colonies of beta haemolytic streptococci were emulsified with chemical matrix on the sample slide, dried and analyzed by MALDI-TOF-MS. The reproducibility of results for all groups of beta haemolytic streptococci was good and spectra obtained for Lancefield group A, C and G streptococci showed discrimination between the groups on visual comparison. A finer difference in spectrum was observed among group A streptococci isolated from different locations at different periods of time. MALDI-TOF-MS may be a potential tool in discriminating between strains of beta haemolytic ...
Rapid Communications in Mass Spectrometry, 2005
ABSTRACT The gas-phase acidities (GA) of a series of dicarboxylic acids were estimated by applyin... more ABSTRACT The gas-phase acidities (GA) of a series of dicarboxylic acids were estimated by applying the extended kinetic method. Proton-bound heterodimeric anions [A−H+B−] of a series of dicarboxylic acids (A) and reference compounds (B) were generated under electrospray ionization conditions, and the dissociation of these cluster ions was examined using a triple-quadrupole mass spectrometer. The mass-selected proton-bound heterodimeric anions were fragmented to yield individual monomer anions as the only product ions, and the abundance ratios of these anions were used to estimate the GA values of the dicarboxylic acids. The experiment was performed over a range of collision energies in order to more accurately determine GA values and to estimate the differences in the entropy of deprotonation of the dicarboxylic acids and the reference compounds. The trends in GA values obtained for the dicarboxylic acids could imply cyclization of the structures via intramolecular hydrogen bonding. The lower homologues show higher GA values than the higher homologues. The GA order for lower homologues is comparable with that of their solution-phase pKa1 values. Copyright © 2005 John Wiley & Sons, Ltd.
Tetrahedron, 1998
cis,syn,cis-Triquinane diol 1, with its folded topology, hydrophobic posterior and inwardly direc... more cis,syn,cis-Triquinane diol 1, with its folded topology, hydrophobic posterior and inwardly directed endo,endo-hydroxy groups, readily enters into cyclooligomerization reaction with terephthaloyldichloride 4. As many as nine cyclic oligomers A-I, with macrocyclic ring size varying from 28- to 98-membered, have been isolated and characterized. The cyclic oligomers exhibit interesting spatial relationships through the relative orientation of methylene groups on the central
Special Paper 356: Catastrophic events and mass extinctions: impacts and beyond, 2002
Tetrahedron: Asymmetry, 2003
Synthetic Communications, 1980
... at 190°C in an evacuated sealed tube fOr,4 hrs. Dlels-Alder adduct a, mp 155OC (27%) and CL c... more ... at 190°C in an evacuated sealed tube fOr,4 hrs. Dlels-Alder adduct a, mp 155OC (27%) and CL crystalline product 20 which melts at l58OC (28.5$) The t NCL Communlca tion !io. 2458 843 Copyriat 0 1980 by Marcel Dekker, Inc. Page 2. AFZAL ET AL. a44 were Isolated. ...
Rapid Communications in Mass Spectrometry, 2004
The gas-phase coordination behavior of the [Cr(III)(Salen)]PF(6) complex at the free axial positi... more The gas-phase coordination behavior of the [Cr(III)(Salen)]PF(6) complex at the free axial positions has been studied in the presence of amines as ligands (propylamine and a series of diamines) under electrospray ionization conditions. The [Cr(III)(Salen)](+) complex formed stable five- and six-coordinated complex ions, [Cr(III)(Salen)(L)](+) and [Cr(III)(Salen)(L)(2)](+), respectively, where L = solvent molecule or amine. When diamines were used as ligands, abundant [Cr(III)(Salen)(L)](+) ions were observed in which two axial positions of the [Cr(III)(Salen)](+) species are occupied by the two amino groups of the diamine ligand. The relative abundances of ligated complex ions, fragment ions, and solvent adducts of fragment ions in the ESI mass spectra, were found to depend on the cone voltage used to record the spectrum. The ESI mass spectra of [Cr(III)(Salen)](+) in the presence of diamines as ligands, and experiments on ligand-pickup in the collision cell, clearly demonstrated that the [Cr(III)(Salen)(L)](+) complex ion is stable for 1,2-diaminoethane and 1,3-diaminopropane. The stability of [Cr(III)(Salen)(L)](+) ions gradually decreased from 1,4-diaminobutane to 1,6-diaminohexane, and then showed a slight increase for 1,7-diaminoheptane and 1,8-diaminooctane. The collision-induced dissociation spectra of [Cr(III)(Salen)(L)](+) ions support the above observations.
Rapid Communications in Mass Spectrometry, 2007
Diastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)-6-(N-carbomethoxyamino) 1,2-O-isopr... more Diastereomeric conduramine derivatives, i.e., (1R,2S,3R/S,6S)-6-(N-carbomethoxyamino) 1,2-O-isopropylidenecyclohex-4-ene-1,2,3-triol (1 and 2) and their O-acetyl derivatives (3 and 4), were studied using gas chromatography (GC) with electron ionization (EI) and chemical ionization (CI). The EI mass spectra of diastereomeric pairs show consistent differences in the relative abundances of characteristic ions. The EI fragmentation patterns are based on precursor/product ion spectra, high-resolution mass spectrometry (HRMS) and deuterium labelling. The CI spectra show differences from the EI spectra, and the isobutane/CI spectra are much simpler than the methane/CI spectra. The differences shown in the CI spectra are similar to those shown in the product ion spectra of [M+H](+) ions generated under electrospray ionization (ESI) conditions. Theoretical calculations are performed to understand the observed differences. The differences in the relative stabilities of molecular ions, or protonated molecules at different sites, can explain the observed differences in the spectra.