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S Rajagopal

Publications and source records attributed to S Rajagopal.

At least 19 recordsLinked to original sources
PubMed2006

Photoluminescence electron-transfer quenching of rhenium(I) rectangles with amines.

Electron-transfer (ET) reactions from aromatic amines to excited states of rhenium(I)-based molecular rectangles [{Re(CO)3(mu-bpy)Br}{Re(CO)3(mu-L)Br}]2 (bpy = 4,4'-bipyridine, L = 4,4'-dipyridylacetylene (dpa), I; L = 4,4'-dipyridylbutadiyne (dpb), II; and L = 1,4-bis(4'-pyridylethynyl)benzene (bpeb), III) were investigated in a dichloromethane solution using luminescence quenching techniques. Direct evidence for the ET reaction was obtained from the detection of the amine cation radical in this system using time-resolved transient absorption spectroscopy. The values of the luminescence quenching rate constants, kq, of the 3MLCT excited state of Re(I) rectangles with amines were found to be higher than those for the monomeric Re(I) complexes and other Re(I)-based metallacyclophanes. The observed kq values were correlated well with the driving force (Delta G degrees) for the ET reactions. In addition, a semiclassical theory of ET was successfully applied to the photoluminescence quenching of Re(I) rectangles with amines.

Journal Article↗
PubMed2006

Control of modiolid mussels in cooling water systems by continuous chlorination.

Modiolid mussels such as Modiolus philippinarum and Modiolus metcalfei constitute a numerically significant group in fouling communities, especially in tropical and subtropical industrial cooling water systems. Nevertheless, there are hardly any published reports on the tolerance of these species to chlorination or biofouling control measures, This article provides data on the mortality pattern (LT(50) and LT(100)) and physiological activities (oxygen consumption, filtration rate, foot activity, and byssus thread production) of different size groups of M. philippinarum (7- to 30-mm shell lengths) and M. metcalfei (6- to 26-mm shell lengths) exposed to different concentrations of residual chlorine (0.25, 0.50, 0.75, and 1.00 mg/L for sublethal responses; 1, 2, 3, and 5 mg/L for mortality). It is shown that exposure time for 100% mortality of M. philippinarum and M. metcalfei significantly decreased with increasing residual chlorine concentration. For example, 30-mm size group M. philippinarum exposed to 1 mg/L chlorine residual took 402 h to reach 100% mortality, whereas those exposed to 5 mg/L chlorine took 108 h. Among the two mussels, M. philippinarum showed slightly higher tolerance (9-20%) to chlorine when compared to M. metcalfei. The effect of mussel size on mortality of M. philippinarum was significant, with the larger size group mussels showing greater resistance than smaller ones. However, in M. metcalfei, size of the mussel does not seem to be a determinant of its chlorine tolerance. All size groups of M. philippinarum and M. metcalfei showed progressive reduction in physiological activities (oxygen consumption, filtration rate, foot activity index, and byssus thread production) when chlorine residuals gradually increased from 0 to 1 mg/L. Reduction in physiological activities was strongly correlated with chlorine concentration. A comparison of present data with data available for other coexisting mussel species suggests that M. philippinarum and M. metcalfei are relatively less tolerant to chlorine than Perna viridis, Perna perna, and Brachidontes striatulus, which also cause fouling problems in tropical coastal waters.

Animals↗
PubMed2006

Mussel colonization of a high flow artificial benthic habitat: byssogenesis holds the key.

Water flow is an important characteristic determining the settlement and growth of macro-invertebrates in the marine environment. Intake systems of coastal power stations offer a unique opportunity to study the effect of water flow on benthic organisms under field conditions. The cooling water intake system of a tropical coastal power station is used as an experimental facility to study the effect of flow on the recruitment and growth of three mussel species, viz, Brachidontes variabilis, B. striatulus, and Modiolus philippinarum. The study was prompted by earlier observation that these mussels were numerically abundant in the biofouling community present inside the seawater intake tunnel of the power station, even though their occurrence in the benthic community in the coastal waters outside was only nominal. Recruitment data showed that the three mussel species very successfully colonised surfaces exposed to the intake mouth (characterised by relatively high flow) of the power station. Significant difference was observed in the recruitment recorded at the intake point and the ambient environment outside. Under high flow condition, the growth rates of all the three mussel species were uniformly enhanced. It is argued that recruitment of the different species is related to the number of byssus threads produced by each mussel and the strength of the byssus threads. The results indicate that byssus number and byssus strength of the mussels are important criteria that decide successful colonization and establishment in high flow environments.

Adaptation, Physiological↗
PubMed2006

Schwannoma of the nasal septum.

Schwannomas of the nasal cavity and paranasal sinuses are very rare. We report the case of a 54-year-old woman with a schwannoma arising from the nasal septum. We discuss the clinical presentation, differential diagnosis, imaging characteristics and treatment of this rarely encountered lesion.

Female↗
PubMed2005

Micellar catalysis on the electron transfer reactions of iron(III)-polypyridyl complexes with organic sulfides-importance of hydrophobic interactions.

The oxidation of organic sulfides with iron(III)-polypyridyl complexes [Fe(NN)3]3+ proceeds through an electron transfer mechanism and an increase in the methanol content in the methanol-water mixture favors the reaction. The reaction is catalyzed by both the anionic surfactant, sodium dodecyl sulfate (SDS) and the cationic surfactant, cetyltrimethylammonium bromide (CTAB). The micellar catalysis in the presence of SDS is accounted for in terms of strong binding of the cationic oxidant with the anionic surfactant and the development of positive charge on sulfur center of substrate in the transition state. The micellar catalysis observed on the reaction involving a trication, [Fe(NN)3]3+, in the presence of CTAB indicates the importance of hydrophobic interaction between the micelle and hydrophobic ligand of [Fe(NN)3]3+. The micellar catalysis is explained in terms of a pseudophase ion exchange model.

Journal Article↗
PubMed2005

Upper temperature tolerances of exotic brackish-water mussel, Mytilopsis leucophaeata (Conrad): an experimental study.

The dark false mussel, Mytilopsis leucophaeata is an important mussel colonising the brackish-water systems of temperate and subtropical regions. Of late it has earned notoriety as a biofouling species in industrial cooling water systems. However, there are no published data on the temperature tolerance of this species. This paper presents data on the upper temperature tolerance of this mussel from the view point of biofouling control using thermal methods. In addition to mortality, response of physiological activities such as oxygen consumption, filtration rate, foot activity and byssus thread production were also studied at temperatures varying from 5 to 35 degrees C. Experiments were also carried out to understand the effect of mussel size, breeding condition, nutritional status and acclimation conditions (temperature and salinity) on the mortality pattern. The physiological activities were significantly reduced at temperatures beyond 27.5 degrees C and ceased at 35 degrees C. In 20 mm size group mussels exposed to 37 degrees C, 50% mortality was observed after 85 min and 100% mortality after 113 min. The effect of mussel size on mortality at different temperatures was significant, with the larger size group mussels showing greater resistance. M. leucophaeata collected during the non-breeding season (December-April) were more tolerant to temperature than those collected during the breeding season (June-October). Nutritional status of the mussel had no significant influence on the thermal tolerance of the mussel: fed and starved (non-fed) mussels succumbed to temperature at comparable rates. The effect of acclimation temperature and acclimation salinity on M. leucophaeata mortality at different temperatures was significant. Survival time increased with increasing acclimation temperature and decreased with increasing salinity. In comparison with other co-occurring species such as Mytilus edulis and Dreissena polymorpha, M. leucophaeata appears to be more tolerant to high temperature stress.

Adaptation, Physiological↗
PubMed2005

Byssal detachment underestimates tolerance of mussels to toxic compounds.

Mussels are sedentary organisms attached to solid substrata by means of byssus threads. Mussels detached from their substratum tend to reattach by producing new byssus threads. Therefore, in bioassays using mussels, if the test animals are in an unattached status, increased byssogenic activity would expose their soft body parts to the toxic compound used. We test the tolerance of two mussel species (Mytilopsis leucophaeata and Mytilus edulis) to an oxidizing biocide (chlorine) and show that detached mussels are 24-28% less tolerant than byssally attached ones. Detached mussels also showed higher oxygen consumption, filtration rate, foot activity, byssus thread production and byssogenesis index, parameters which are associated with valve opening. A review of literature showed that most of the published data on toxicity against heavy metals and biocides are generated using unattached mussels. The data, therefore, represent an underestimation of the toxicity of the tested compound. Correction data are presented for chlorine tolerance of Dreissena polymorpha, Mytilopsis leucophaeata and Mytilus edulis. The present study suggests the importance of maintaining mussels in their attached status, while undertaking toxicity bioassays.

Analysis of Variance↗
PubMed2005

Factors influencing the upper temperature tolerances of three mussel species in a brackish water canal: size, season and laboratory protocols.

Mussels are the most problematic organisms encountered in the water intake systems of electrical power plants. Various fouling control measures are adopted, among which heat treatment is considered the relatively more attractive from economic and ecological points of view. Thermal tolerance experiments were carried out to determine the effects of mussel size (2-20 mm shell length), season (breeding vs non-breeding), nutritional status (fed vs non-fed), acclimation temperature (5-25 degrees C) and acclimation salinity (1-35%o) on the mortality pattern of three important mussel species, viz. a freshwater mussel Dreissena polymorpha, a brackish water mussel Mytilopsis leucophaeata and a marine mussel Mytilus edulis under different temperatures (36-41 degrees C). The mussels in the 10 mm size group exposed to 36 degrees C showed 100% mortality after 38 min (D. polymorpha), 84 min (M. edulis) and 213 min (M. leucophaeata). The effect of mussel size on M. edulis and M. leucophaeata mortality at different temperatures was significant, with the largest size group of mussels showing greater resistance, while no significant size-dependence was observed in the case of D. polymorpha. All the three mussel species collected during the non-breeding season (June-October). Nutritional status had no significant influence on the thermal tolerance of the three mussels; fed and non-fed mussels showed 100% mortality at comparable rates. Acclimation temperature had a significant effect on the mortality of all three species. Survival time at any given target temperature increased with increasing acclimation temperature. The acclimation salinity showed no significant effect on the thermal tolerance of the three mussel species. In comparison, M. leucophaeata was more tolerant to high temperature stress than the other two species. The present studies clearly show that various factors can influence the mortality of D. polymorpha, M. edulis and M. leucophaeata to elevated temperatures. The results, therefore, suggest that if heat treatment were to be used as a control measure for these mussels, it has to be employed judiciously, depending on the mussel species, mussel size, breeding season, water temperature and salinity.

Acclimatization↗
PubMed2004

Coordination chemistry of chromium-Salen complexes studied by electrospray ionization mass spectrometry.

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.

Journal Article↗
PubMed2004

Private sector hospital response to the 2003 dengue outbreak in the Indian capital metropolis of Delhi.

During 2003, the Indian capital metropolis of Delhi was afflicted with an outbreak of dengue. A private-sector tertiary care hospital responded instantly to the sudden influx of 162 patients during an 8-week interval. That was an unusual challenge because, until 1997, the hospital had exclusively managed patients with ophthalmic disorders. Dengue patients received fiscal concessions and several free services. A multidisciplinary cell was commissioned for case management. Apart from a diagnosis of patients with dengue and their clinical management, suspected or confirmed dengue episodes were instantly reported to health authorities. Anti-mosquito measures in the hospital premises including residential areas for the nursing personnel prevented any local virus transmission. The integrated therapeutic and public health response was associated with a 1.23% case fatality rate. The protocol developed during the dengue outbreak would address every locally reportable disease in the future.

Adolescent↗
PubMed2004

Anticancer and immunostimulatory compounds from Andrographis paniculata.

Andrographis paniculata extract is traditionally used as a medicine to treat different diseases in India, China and Southeast Asia. In the present study, we evaluated the anticancer and immunomodulatory activity of the methanolic extract of Andrographis paniculata in human cancer and immune cells. The methanolic extract of Andrographis paniculata was fractionated into dichloromethane, petroleum ether and aqueous extracts and screened for bioactivity. Our results indicate that the dichloromethane fraction of the methanolic extract retains the active compounds contributing for both the anticancer and immunostimulatory activity. Dichloromethane fraction significantly inhibits the proliferation of HT-29 (colon cancer) cells and augments the proliferation human peripheral blood lymphocytes (HPBLs) at low concentrations. On further fractionation of the dichloromethane extract we could isolate three diterpene compounds, i.e. [1] andrographolide, [2] 14-deoxyandrographolide and [3] 14-deoxy-11,12-didehydroandrographolide. Andrographolide showed anticancer activity on diverse cancer cells representing different types of human cancers. Whereas all the three molecules showed enhanced proliferation and interleukin-2 (IL-2) induction in HPBLs.

Adjuvants, Immunologic↗
PubMed2003

Synthesis and photophysical properties of neutral luminescent rhenium-based molecular rectangles.

A series of neutral luminescent molecular rectangles [[Re(CO)(3)(mu-bpy)Br][Re(CO)(3)(mu-L)Br]](2) (1-4) having fac-Re(CO)(3)Br as corners and 4,4'-bipyridine (bpy) as the bridging ligand on one side and other bipyridyl ligands of varying length (L) on the other side have been synthesized and characterized. The crystal structure of 1 shows a rectangular cavity with the dimensions of 11.44 x 7.21 A. When the cavity size is tuned from 1 to 4, a dimension of 11.4 x 20.8 A could be achieved, as revealed by the molecular modeling. These rectangles exhibit luminescence in solution at room temperature. In particular, compound 4 containing 1,4-bis(4'-pyridylethynyl)benzene (bpeb) as bridging ligand shows the excited-state lifetime of 495 ns. Fine-tuning of the cavity size of the rectangles improves their excited-state properties. These properties facilitate the study of excited-state electron-transfer reactions with electron acceptors and donors and host-guest binding. Crystallographic information: 1.6CH(3)COCH(3) is monoclinic, P2(1)/c, with a = 12.0890(2), b = 24.2982(2), and c = 12.8721(2) A, beta = 107.923(1) degrees, and Z = 2.

Journal Article↗
PubMed2003

Self-assembly of octarhenium-based neutral luminescent rectangular prisms.

Self-assembly of rhenium-based nanoscale rectangular prismatic boxes has been achieved in quantitative conversion. The fac-rhenium corner provided three mutually perpendicular coordination sites and served as a good candidate for the construction of 3-D boxes. These are the first Re-based, neutral, luminescent prisms of M(8)L(2)L'(8) type that has been characterized crystallographically. Their luminescent properties and molecular recognition capabilities make these molecular prisms interesting supramolecules.

Journal Article↗
PubMed2003

Response of fouling brown mussel, Perna perna (L.), to chlorine.

Perna perna (L.), the edible brown mussel, is very widely distributed in the tropical and subtropical regions and is commonly found in rocky shores. Apart from being a candidate for commercial cultivation, P. perna is also a common pest organism in cooling water systems of coastal power stations. Therefore, a lethal and sublethal response of this mussel to commonly used antifouling biocides is of considerable interest to the industry. Mortality pattern (LT(50) and LT(100)) and physiological activities (oxygen consumption, filtration rate, foot activity index, and byssus thread production) of different size groups (9-34 mm shell lengths) of P. perna were studied in the laboratory under different residual chlorine concentrations (0.25, 0.50, 0.75, and 1.00 mg/L for sublethal responses and 1, 2, 3, and 5 mg/L for mortality). Results showed that exposure time for 100% mortality of mussels significantly decreased with increasing residual chlorine concentration. For example, mussels of 9 mm size group exposed to 1 mg/L chlorine residual took 384 h (16 days) to reach 100% mortality, whereas those exposed to 5 mg/L chlorine took 84 h (4 days). The effect of mussel size on mortality was significant between 1 mg/L and 5 mg/L residual chlorine, with larger mussels showing greater resistance than smaller ones. For example, at 2 mg/L residual chlorine, 9 mm and 34 mm size group mussels took 228 h (10 days) and 304 h (13 days), respectively, to achieve 100% mortality. All size groups of P. perna showed progressive reduction in physiological activities, when chlorine residuals were gradually increased from 0 to 1 mg/L. Reduction in physiological activities was strongly correlated with the residual level. A comparison of present data with data available for other common fouling organisms suggests that P. perna is relatively less tolerant to chlorine than Perna viridis (L.) and Brachidontes striatulus (Hanley), which also cause fouling problems in tropical coastal waters.

Animals↗
PubMed2003

Tolerance of five species of tropical marine mussels to continuous chlorination.

The paper examines the relative lethal and sublethal response of five important tropical marine mussels (Perna viridis, Perna perna, Brachidontes striatulus, Brachidontes variabilis and Modiolus philippinarum) to different chlorine concentrations varying from 0.25 to 15 mg l(-1). The mussels were observed to co-exist in the cooling water circuits of a coastal power station that adopted intermittent chlorination as a fouling control technique. The five mussel species showed, in response to chlorination, 100% mortality at significantly different exposure times, indicating significant species-specific variability in chlorine tolerance. For example, at 1 mg l(-1) residual chlorine, B. variabilis and P. viridis took 288 and 816 h, respectively, to achieve 100% mortality. The time taken for 100% mortality decreased with increasing chlorine residual concentration. The effect of mussel size (= mussel age) of P. viridis, P. perna, B. striatulus and M. philippinarum on mortality was significant between 1 and 5 mg l(-1) residual chlorine, with larger mussels showing greater resistance than smaller ones. All mussel species showed progressive reduction in physiological activities when chlorine residuals were increased from 0 to 1 mg l(-1). However, species-specific differences in the relative rate of physiological activities were observed. Accordingly, relative reduction in physiological activities in response to chlorination was the lowest in P. viridis and the highest in B. variabilis. The data clearly indicate significant differences in the lethal and sublethal responses of the five mussel species to chlorination. The results, therefore, suggest that for effective fouling control, chlorine treatment against mussels has to be employed judiciously, depending on the mussel species involved.

Age Factors↗
PubMed2003

Comparative chlorine and temperature tolerance of the oyster Crassostrea madrasensis: implications for cooling system fouling.

Crassostrea madrasensis is an important fouling oyster in tropical industrial cooling water systems. C. madrasensis individuals attach to surfaces by cementing one of their two valves to the substratum. Therefore, oyster fouling creates more problems than mussel fouling in the cooling conduits of power stations, because unlike the latter, the shell of the former remains attached to the substratum even after the death of the animal. However, there are no published reports on the tolerance of this species to chlorination and heat treatment. The mortality pattern and physiological behaviour (oxygen consumption and filtration rate) of three size groups (13 mm, 44 mm and 64 mm mean shell length) of C. madrasensis were studied at different residual chlorine concentrations (0.25, 0.5, 0.75, 1, 2, 3 to 5 mg 1-1) and temperatures (30 degrees C to 45 degrees C). The effect of shell size (= age) on C. madrasensis mortality in the presence of chlorine and taking into account temperature was significant, with the largest size group oysters showing highest resistance. At 1 mg l-1 residual chlorine, the 13 mm and 64 mm size group oysters, took 504 h (21 d) and 744 h (31 d), respectively to reach 100% mortality. At 39 degrees C, the 13 mm size group oysters took 218 min to reach 100% mortality, whereas the 64 mm size group oysters took 325 min. The oxygen consumption and filtration rate of C. madrasensis showed progressive reduction with increasing residual chlorine concentrations. However, the filtration rate and oxygen consumption responses of C. madrasensis were not significantly different between 30 degrees C (control) and 37.5 degrees C. There was a sharp decrease in the filtration rate and oxygen consumption at 38.5 degrees C. A comparison of the present mortality data with previous reports on other bivalves suggests that the chlorine tolerance of C. madrasensis lies in between that of Perna viridis and Perna perna, while its temperature tolerance is significantly higher than that of the other two bivalve species. However, in power station heat exchangers, where simultaneous chlorine and thermal stresses are existent, C. madrasensis may have an edge over other common foulants, because of its high temperature tolerance.

Analysis of Variance↗