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Alwyn G. Davies Rajaveen Sivasubramaniam 《Journal of organometallic chemistry》2006,691(16):3556-3561
The thermolysis of the butyltin chlorides at 200-300 °C in the liquid phase has been investigated by 1H, 13C, and 119Sn NMR spectroscopy. The stabilities follow the order: Bu2SnCl2 > Bu3SnCl > BuSnCl3. Only tributyltin chloride showed any evidence of redistribution, giving dibutyltin dichloride, together with metallic tin, butane, and but-1-ene, which would be formed by decomposition of tetrabutyltin. Dibutyltin dichloride decomposed to give mainly butane with no other apparent liquid organotin compound. Butyltin trichloride gave butane, some butene, and metallic tin, and showed no evidence of forming tributyltin chloride by the redistribution reaction, which would have environmental implications for its use in the CVD coating of glass. 相似文献
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Varatharajan Sabareesh Padmanabhan Balaram 《Rapid communications in mass spectrometry : RCM》2007,21(19):3227-3227
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The fragmentations of [M+H]+ and [M+Na]+ adducts of neutral peptides with blocked N- and C-termini have been investigated using electrospray ion trap mass spectrometry. The N-termini of these synthetically designed peptides are blocked with a tertiarybutyloxycarbonyl (Boc) group, and the C-termini are esterified. These peptides do not possess side chains that are capable of complexation and hence the backbone amide units are the sole sites of protonation and metallation. The cleavage patterns of the protonated peptides are strikingly different from those of sodium ion adducts. While the loss of the N-terminal blocking group occurs quite readily in the case of MS/MS of [M+Na]+, the cleavage of the C-terminal methoxy group seems to be a facile process in the case of MS/MS of [M+H]+ * Fragmentation of the protonated adducts yields only bn ions, while yn and a(n) ions are predominantly formed from the fragmentation of sodium ion adducts. The a(n) ions arising from the fragmentation of [M+Na](+) lack the N-terminal Boc group (and are here termed a(n)* ions). MS/MS of [M+Na]+ species also yields b(n) ions of substantially lower intensities that lack the N-terminal Boc group (b(n)*). A similar distinction between the fragmentation patterns of proton and sodium ion adducts is observed in the case of peptides possessing an N-terminal acetyl group. An example of the fragmentation of the H+ and Na+ adducts of a naturally occurring peptaibol from a Trichoderma species confirms that fragmentation of these two ionized species yields complementary information, useful in sequencing natural peptides. Inspection of the isotopic pattern of b(n) ions derived from [M+H]+ adducts of peptaibols provided insights into the sequences of microheterogeneous samples. This study reveals that the combined use of protonated and sodium ion adducts should prove useful in de novo sequencing of peptides, particularly of naturally occurring neutral peptides with modified N- and C-termini, for example, peptaibols. 相似文献
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Sengupta A Roy RS Sabareesh V Shamala N Balaram P 《Organic & biomolecular chemistry》2006,4(6):1166-1173
The crystal structures of four protected beta-amino acid residues, Boc-(S)-beta3-HAla-NHMe (1); Boc-(R)-beta3-HVal-NHMe (2); Boc-(S)-beta3-HPhe-NHMe (3); Boc-(S)-beta3-HPro-OH (6) and two beta-dipeptides, Boc-(R)-beta3-HVal-(R)-beta3-HVal-OMe (4); Boc-(R)-beta3-HVal-(S)-beta3-HVal-OMe (5) have been determined. Gauche conformations about the C(beta)-C(alpha) bonds (theta approximately +/-60 degrees) are observed for the beta3-HPhe residues in and all four beta3-HVal residues in the dipeptides and . Trans conformations (theta is approximately 180 degrees) are observed for beta3-HAla residues in both independent molecules in and for the beta3-HVal and beta3-HPro residues in and , respectively. In the cases of compounds , molecules associate in the crystals via intermolecular backbone hydrogen bonds leading to the formation of sheets. The polar strands formed by beta3-residues aggregate in both parallel (1,3,5) and antiparallel (2,4 fashion. Sheet formation accommodates both the trans and gauche conformations about the C(beta)-C(alpha) bonds. 相似文献
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Seshadri K.S. Selvaraj M. Kesavamoorthy R. Srinivasan M.P. Varatharajan K. Lal K.B. Krishnasamy V. 《Journal of Sol-Gel Science and Technology》2003,28(3):327-333
An attempt has been made to synthesize ceramic titania and zirconia membranes by sol-gel process by filtering respective viscous colloidal sol through microporous alumina support and gelling followed by sintering at 400°C and 470°C respectively. The static charge on the pores of the so formed membranes and the pore size distribution determine the applicability in filtering colloidal solution. The mean pore size from SEM were found to be 0.65 m and 0.54 m for titania and zirconia membranes respectively with 1.47 × 107/cm2 as pore density for both. The filtration characteristics during membrane layer formation showed that the membrane layer formation started after 35 minutes in the case of titania membrane and 40 minutes in the case of zirconia membrane. From the gravimetric estimation of water content of the membranes the thickness of the membrane was found out to be 3 m and the porosity was found out to be 0.30 for both the cases. The particle charge density was estimated from the zeta potential and the particle size. The pore charge density was estimated from the particle charge density, pore density, pore diameter and the thickness of the membrane layer. The membrane pore charge density was found to vary between 3 to –1 Coulombs/cm2 in the case of titania membrane and 7 to –0.5 Coulombs/cm2 in the case of zirconia membrane in the pH range 1–12. 相似文献
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Mark S. Squillante Yanyong Zhang Anand Sivasubramaniam Natarajan Gautam 《Annals of Operations Research》2008,160(1):227-255
This paper introduces a generalization of the classical parallel-server fork-join queueing system in which arriving customers
fork into multiple tasks, every task is uniquely assigned to one of the set of single-server queues, and each task consists
of multiple iterations of different stages of execution, including task vacations and communication among sibling tasks. Several
classes of dynamic polices are considered for scheduling multiple tasks at each of the single-server queues to maintain effective
server utilization. The paper presents an exact matrix-analytic analysis of generalized parallel-server fork-join queueing
systems, for small instances of the stochastic model, and presents an approximate matrix-analytic analysis and fixed-point
solution, for larger instances of the model. 相似文献
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Pumadevi Sivasubramaniam 《Research in Mathematics Education》2013,15(1):169-190
This paper reoprts on one aspect of recent research on students' understanding of graphs in computer and in pencil and paper media. Over 200 Year 10 [age 14–15] students in two comprehensive schools in Leeds participated in a learning experiment, 100+ with and 100+ without the use of computers. Pre, post and delayed post-tests and interviews provide data for a comparison of learning with the two media. 相似文献
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Varatharajan Sivasubramaniam Florian Brodkorb Stephanie Hanning Oliver Buttler Hans Peter Loebl Volker van Elsbergen Herbert Boerner Ullrich Scherf Martin Kreyenschmidt 《Solid State Sciences》2009,11(11):1933-1940
Different analytical tools and methodologies are currently employed to determine degradation products of organic blue light emitting devices in order to identify the failure mechanisms which determine the lifetime of these devices. This article provides a deeper understanding of degradation mechanisms of organic light emitting diodes (OLEDs) during device operation. Degradation products of blue emitting devices containing 8% of the phosphorescent emitter iridium(III)bis(4,6-difluorophenyl)-pyridinato-N,C2′ picolinate (FIrpic) in a matrix containing bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminium (BAlq) as electron transport layer (ETL), 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA) and N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4″-diamine (α-NPD) were investigated using laser desorption ionization (LDI) coupled with a time of flight mass spectrometry (TOF/MS). Especially chemical degradation pathways of the hole transport materials TCTA and α-NPD were investigated. The comparison of experimental data of unstressed and stressed device revealed that new reaction products are formed during the device operation. The linkage of TCTA fragments to the α-NPD core in an interfacial reaction as well as a dimerization of TCTA itself was observed. Ten new reaction products could be characterized via LDI-TOF-MS. Some of these compounds might possess a negative influence on the drop of efficiency and lifetime of blue light emitting devices based on FIrpic. 相似文献