Posted by admin on 13th February 2007
| P. Manoj 1, K. P. Prasanthkumar 1, V. M. Manoj 1, Usha K. Aravind 1, T. K. Manojkumar 2, C. T. Aravindakumar 1 * |
1School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, Kerala, India
2Indian Institute of Information Technology and Management-Kerala, Technopark Campus, Thiruvananthapuram 695 581, Kerala, India |
| email: C. T. Aravindakumar (CT-Aravindakumar@rocketmail.com) |
*Correspondence to C. T. Aravindakumar, School of Chemical Sciences, Mahatma Gandhi University, Kottayam 686 560, Kerala, India.
| triazine • sulfate radical anion • laser flash photolysis • radiation chemical • DFT calculation • radical cation • pollutant |
Laser flash photolysis has been used to determine the bimolecular rate constants and the spectral nature of the intermediates obtained by the reaction of sulfate radical anion (SO4- ) with 1,3,5-triazine (T), 2,4,6-trimethoxy-1,3,5-triazine (TMT), 2,4-dioxohexahydro-1,3,5-triazine (DHT), and 6-chloro N-ethyl N’-(1-methylethyl)-1,3,5-triazine-2,4-diamine (atrazine, AT). The rate constants determined were in the range 4.6 × 107-3 × 109 dm3 mol-1 s-1 at pH 6. The transient absorption spectra obtained from the reaction of SO4- with T, TMT, DHT and AT has an absorption maximum in the region 320-350 nm and was found to undergo second-order decay. The intermediate species is assigned to N-yl C(OH) radical of T (TOH
), carbon centered neutral radical of TMT, an OH-adduct of AT and an N-centered radical in the case of DHT. The interpretations on the experimental results obtained from TMT are supported by DFT calculation using Gaussian 03. Steady state radiolysis technique has also been used to investigate the degradation of AT induced by SO4-. The degradation profile indicated that about 99% of AT has been decomposed after an absorbed gamma-radiation dose of 7.5 kGy. The degradation yield of AT (expressed as G(-AT)) was found to be 0.26 µ mol J-1. The degradation reactions initiated by SO4- may thus be employed as a potential alternative for OH-induced degradation of triazines.
Copyright © 2007 John Wiley & Sons, Ltd.
The Abstract has been published at Wiley InterScience website and can be accessed from this link:
http://www3.interscience.wiley.com/cgi-bin/abstract/114102851/ABSTRACT
Posted in Organic chemistry, General Publications | Submit Comment
Posted by admin on 10th August 2006
A simple time delay model for eukaryotic cell cycle
J. Srividhyaa and M.S. Gopinathanb
aIndiana University School of Informatics, Indiana University, Bloomington, IN 47406, USA
bIndian Institute of Information Technology and Management Kerala, Thiruvananthapuram, Kerala 695581, India
Received 7 March 2005; revised 19 December 2005; accepted 28 December 2005. Available online 13 February 2006.
Abstract
We propose a seven variable model with time delay in one of the variables for the cell cycle in higher eukaryotes. The model consists of four important phosphorylation–dephosphorylation (P–D) cycles that govern the cell cycle, namely Pre-MPF-MPF, Cdc25P-Cdc25, Wee1P-Wee1 and APCP-APC. Other variables are cyclin, free cyclin dependent kinase (Cdk) and mass. The mass acts as a G2/M checkpoint and the checkpoint is represented by a saddle node loop bifurcation.
The key feature of the model is that a time lag has been introduced in the activation of anaphase promoting complex (APC) by maturation promoting factor (MPF). This is effected by treating MPF as a time-delayed variable in the activation step of APC. The time lag acts as a spindle checkpoint. Absence of time delay induces a bistability in our model. Time delay also brings about variability in G1 phase timings. The model also reproduces the mutant phenotype experiments on wee1 cells.
Stochasticity has been introduced in the model to simulate the dependence of the cycle time on cell birth length. Mutant phenotypes in the stochastic model reproduce the experimental observations better than the deterministic model.
Keywords: Cell division cycle; P–D cycles; Positive feedback; Time delay; G1/S and G2/M transitions; Bistability
Original Abstract :
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WMD-4J84T45-1&_coverDate=08%2F07%2F2006&_alid=433602423&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=6932&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=4d0f55b7080acb1fe7ee3c0368eb9d98
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Posted by admin on 10th August 2006
Research Article
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Redox chemistry of 8-azaadenine: a pulse radiolysis study
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| G. Pramod 1, H. Mohan 2, P. Manoj 1, T. K. Manojkumar 1, V. M. Manoj 1, J. P. Mittal 2, C. T. Aravindakumar 1 * |
1School of Chemical Sciences, Mahatma Gandhi University, Kottayam, Kerala, India
2Radiation Chemistry and Chemical Dynamics Division, Bhabha Atomic Research Centre, Mumbai, India |
| email: C. T. Aravindakumar (CT-Aravindakumar@rocketmail.com) |
*Correspondence to C. T. Aravindakumar, School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills, P.O. Kottayam 686560, Kerala, India.
setDOI(”ADOI=10.1002/poc.1100″)Funded by:
Board of Research in Nuclear Sciences (BRNS), Mumbai
| 8-Azaadenine • redox chemistry • free radicals • radiation chemical • pulse radiolysis • OH-adducts • N-centered radicals • C-centered radicals |
Aza derivatives of purines and pyrimidines are important class of compounds, which are known for their cytotoxic, antimicrobial, and mutagenic activities. The redox chemistry of 8-azaadenine (8AA) has been investigated using pulse radiolysis technique. The oxidation reactions were studied using hydroxyl radical (.OH), oxide radical anion (O.- and sulfate radical anion (SO4.-), and the reduction reactions were studied using hydrated electron (e ) and hydrogen radical (H.). In the reaction of .OH, a bimolecular rate constant of 3.8 × 108 dm3 mol-1 s-1 was determined at pH 6.0. The transient spectrum obtained for the reaction of .OH at pH 6 has an absorption maximum around 340 nm and is assigned to the formation of 8AA-4OH.. The charge population density was calculated theoretically (using Gaussian 98) and it showed that the fourth carbon atom (C(4)) is the most probable site for the attack of .OH. The oxidizing nature of this radical is demonstrated by its reaction with N,N,N ,N-tetramethyl-p-phenylenediamine (TMPD). The existence of this species is further supported by theoretical calculations where the absorption maximum of this radical is calculated as 338 nm. The yield of 8AA-4OH. is estimated as around 85%. At pH 10.2, the transient spectrum with maxima at 300 and 350 nm is attributed to the dehydrated 8AA-4OH., which is an N-centered radical of the type 8AA-N(9).. In the reaction of O.- (pH  14) a transient spectrum with similar features is observed. Therefore this is also assigned to 8AA-N(9).. A bimolecular rate constant for this reaction is determined as 4.2 × 108 dm3 mol-1 s-1. In the reaction of SO4.- at pH 6, the transient spectrum having  max at 320 nm is attributed to the formation of a neutral radical of 8AA (8AA-N(6).), which is formed by the deprotonation of the initially formed radical cation. But at pH 10.2, the spectrum is found to be similar to the one observed in the reaction of O.- and hence it is assigned to the formation of the nitrogen-centered radical 8AA-N(9).. In the reaction of e, a second-order rate constant of 1.8 × 1010 dm3 mol-1 s-1 is determined at pH 6 and the transient absorption spectrum with max at 330 nm is assigned to the protonated electron adduct of 8AA (8AA(NH.)). The reducing nature of this intermediate is confirmed by the formation of methyl viologen radical cation (MV.+) from its reaction with MV2+. The transient intermediate in the case of the reaction of H. is proposed as 8AA-C2(H)N(3). at pH 1.Copyright © 2006 John Wiley & Sons, Ltd.Original Article Abstract : http://www3.interscience.wiley.com/cgi-bin/abstract/112695316/ABSTRACT |
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