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Biomedical subjects

K Balasubramanian

Publications and source records attributed to K Balasubramanian.

At least 19 recordsLinked to original sources
PubMed2006

Electronic states and potential energy curves of molybdenum carbide and its ions.

The potential energy curves and spectroscopic constants of the ground and 29 low-lying excited states of MoC with different spin and spatial symmetries within 48 000 cm(-1) have been investigated. We have used the complete active space multiconfiguration self-consistent field methodology, followed by multireference configuration interaction (MRCI) methods. Relativistic effects were considered with the aid of relativistic effective core potentials in conjunction with these methods. The results are in agreement with previous studies that determined the ground state as X (3)Sigma(-). At the MRCISD+Q level, the transition energies to the 1 (3)Delta and 4 (1)Delta states are 3430 and 8048 cm(-1), respectively, in fair agreement with the results obtained by DaBell et al. [J. Chem. Phy. 114, 2938 (2001)], namely, 4003 and 7834 cm(-1), respectively. The three band systems located at 18 611, 20 700, and 22 520 cm(-1) observed by Brugh et al. [J. Chem. Phy. 109, 7851 (1998)] were attributed to the excited 11 (3)Sigma(-), 14 (3)Pi, and 15 (1)Pi states respectively. At the MRCISD level, these states are 17 560, 20 836, and 20 952 cm(-1) above the ground state respectively. We have also identified a (3)Pi state lying 14 309 cm(-1) above the ground state. The ground states of the molecular ions are predicted to be (4)Sigma(-) and (2)Delta for MoC(-) and MoC(+), respectively.

Journal Article↗
PubMed2006

Multireference configuration interaction study of the electronic states of ZrC.

The potential energy curves and spectroscopic constants of the ground and 32 low-lying electronic states of ZrC have been studied by employing multireference configuration interaction methods, in conjunction with relativistic effective core potentials and 5s3p3d1f, 3s3p1d basis sets con Zr and C, respectively. We have determined that the ground state is (3)Sigma(+). However there are two low-lying (1)Sigma(+) states (below 5000 cm(-1)) which strongly interact resulting in avoided crossings. The lowest (1)Sigma(+) state corresponds to a combination of 1sigma(2) Xsigma(2) 1pi(4) configurations whereas the second is an open shell singlet 1sigma(2) 2sigma(1) 3sigma(1) 1pi(4). Several avoided crossings were observed, for (1)Pi, (3)Pi, (1)Delta, (3)Sigma(+), and (3)Delta states. We have identified (3)Pi and (1)Pi lying at 4367 and 5797 cm(-1), respectively. The results are in good agreement with the recent experimental findings of Rixon et al. [J. Mol. Spectrosc. 228, 554 (2004)], and indicate that the (3)Pi-(3)Sigma(+), and (1)Pi-(1)Sigma(+), bands located between 16 000-19 000 cm(-1) are extremely complex due to near degeneracy of several (1)Pi and (3)Pi states. We also have identified a (1)Sigma(+) state in the same region that may interfere with the (1)Pi emission bands. The present results not only shed further light into the spectra of ZrC but also predict yet to be observed systems.

Journal Article↗
PubMed2006

Investigation of a binuclear gallium complex with bipolar charge transporting capability for organic light-emitting diodes.

Detailed theoretical and experimental investigations have been presented on a novel binuclear gallium complex Ga2(saph)2q2, a potentially active and novel material for organic light-emitting diodes (OLEDs). The density-functional theory has been employed to shed light on the reason why this complex exhibits bipolar character. Theoretical results, such as ionization potential and electron affinity, and optimized geometries are in good agreement with what we have obtained experimentally. Our theoretical analysis provides new insight into the origin of bipolar features. Such character enables the gallium complex to become a prosperous hole and electron transporter used to fabricate single-layer OLEDs, which exhibit better electroluminescence compared with those originated from the previously well-adopted tri(8-hydroxyquinoline)aluminum (Alq3). An OLED device of single Ga2(saph)2q2 layer exhibiting desirable performances has been fabricated, which is in good agreement with the theoretical analysis.

Journal Article↗
PubMed2006

Influence of estradiol on mammary tumor collagen solubility in DMBA-induced rat mammary tumors.

Estradiol plays a vital role in the growth and development of mammary glands. It is a potent stimulator of metabolic processes in normal and carcinoma breast. A critical factor in determining mammary glandular morphology is the stroma. Collagen is a predominant component of the extracellular matrix and cell-collagen interactions are essential carcinogenesis. The present investigation explored the influence of estradiol on collagen solubility and metabolism in mammary tumors during tumor progression and regression. A single injection of 20 mg of 9,10-dimethyl-1,2-benzanthracene was given to rats at 7 weeks of age. With the appearance of the first palpable mammary tumor, the rats were treated with 0.5 microg estradiol or 50 microg tamoxifen daily for 30 days. The rats were sacrificed 24 h after 30 days of treatment. Estradiol appears to stimulate the synthesis of new collagens and thus contributes to the enlargement of the mammary tumors. This might have created a potential microenvironment by increasing the synthesis of suitable matrix that sustains the growth of the mammary tumors. In short, the present findings emphasize a definite mediatory role for collagen in estradiol promoted mammary tumor growth.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2006

Corticosterone impairs the mRNA expression and activity of 3beta- and 17beta-hydroxysteroid dehydrogenases in adult rat Leydig cells.

Clinical and experimental studies, including our own observations, have shown the adverse effects of excess glucocorticoids on testicular steroid hormone production. The present study was designed to gain insight into the molecular mechanisms by which excess corticosterone impairs Leydig cell steroidogenesis. To achieve this, adult rats were administered with corticosterone-21-acetate (2 mg/100 g body weight) twice daily for 15 days. After the treatment period, rats were killed by decapitation. The testes were removed, decapsulated aseptically and used for the isolation of Leydig cells. Purified Leydig cells were used for assessing the activity of 3beta- and 17beta-hydroxysteroid dehydrogenases (HSDs) and total RNA isolation. For in vitro studies, purified Leydig cells (7.5 x 10(6) cells) of control rats were plated in culture flasks and exposed to different concentrations (50, 100, 200, 400, and 800 nmol/L) of corticosterone for 24 h. At the end of incubation, total RNA was isolated from cultured Leydig cells, and the mRNA of 3beta- and 17beta-HSDs was quantified by RT-PCR. A significant reduction in the activities and levels of 3beta-HSD type-I and 17beta-HSD type-III mRNAs in Leydig cells were observed. In vitro studies demonstrated a dose-dependent significant impairment in both the activity and mRNA expression of these enzymes. These results suggest that corticosterone might have a direct effect on the transcription of the genes of 3beta- and 17beta-HSD. It is inferred from the present in vivo and in vitro studies that one of the molecular mechanisms by which excess corticosterone decreases the steroidogenic potency of Leydig cells is by suppressing the mRNA expression of 3beta-HSD type-I and 17beta-HSD type-III enzymes.

17-Hydroxysteroid Dehydrogenases↗
PubMed2006

Effects of excess corticosterone on NADPH generating enzymes and glucose oxidation in Leydig cells of adult rats.

Clinical and experimental studies have shown the adverse effects of excess glucocorticoid on testicular testosterone production. The NADPH co-enzyme has been recognized as an important factor that regulates several steps in steroidogenesis, while glucose oxidation acts as a limiting factor on testicular testosterone production. Nevertheless, the impact of excess corticosterone, the stress hormone on testicular NADPH availability and glucose oxidation is unknown. Therefore, the present study was designed to assess the specific effects of excess corticosterone on Leydig cell NADPH generating enzymes and glucose oxidation. Adult Wistar rats (200-250 g, b.w.) were treated with corticosterone-21-acetate (2 mg/ 100 g, b.w., i.m., twice daily) for 10 days and corticosterone-21-acetate plus luteinizing hormone (LH) (100 microg/kg b.w., i.m., daily) for 10 days. After the treatment period, experimental animals and controls were killed, blood was collected and the sera separated for testosterone assay. Testes were removed and Leydig cells were isolated, purified and used for estimating the specific activity of NADPH generating enzymes and 14C-glucose oxidation. Serum testosterone, Leydig cellular 14C-glucose oxidation and the specific activities of 6-phosphogluconate dehydrogenase (6-PGDH), NADP-isocitrate dehydrogenase (ICDH) and malic enzyme were significantly decreased in corticosterone-treated rats. Co-administration of LH with corticosterone maintained the specific activities of 6-PGDH and ICDH and 14C-glucose oxidation at control level. Nevertheless, serum testosterone and Leydig cellular malic enzyme activity showed a significant decrease in these rats. In conclusion, the inhibitory effects of excess corticosterone on Leydig cell steroidogenesis are mediated through impaired glucose oxidation and defective NADPH generation. Co-administration of LH with corticosterone failed to prevent the decrease in serum testosterone and Leydig cell malic enzyme activity, suggesting the dominant inhibitory effects of excess corticosterone.

Animals↗
PubMed2006

Shock and vibration data acquisition system for off-road vehicle operator health and safety assessment.

A data acquisition software and hardware system was developed for acquiring geo-referenced shock and vibration data using National Instruments' LabView graphical programming language. This was used in conjunction with a modular data acquisition and signal conditioning system and a Differential Global Positioning System (DGPS) receiver. A prototype vehicle obstacle course, which introduced spatially varying shock events to vehicles as they traversed the course, was constructed. Obstacles consisted of both repetitious and single discrete events. A series of investigations was conducted on the obstacle course to evaluate the performance and characteristics of the DAQ system and the tractor when exposed to shock and vibration events. Spectral and time domain plots obtained from the geo-referenced data acquisition system (GDAQ) system under static, highway, and off-road obstacle course conditions were evaluated to demonstrate that the system performed as expected. The migration of experiments from laboratory to field gave confidence that this system could be used to collect shock and vibration data over a wide range of frequencies. The use of geo-referenced data records proved beneficial in isolating and extracting data segments of interest from a continuous data record.

Agriculture↗
PubMed2005

Antioxidant effect of ascorbic acid on PCB (Aroclor 1254) induced oxidative stress in hypothalamus of albino rats.

BACKGROUND: PCBs are one of the environmental toxicants and neurotoxic compounds which induce the production of free radicals leading to oxidative stress. Vitamin C is well known as an outstanding antioxidant. We determined the protective role of ascorbate on hypothalamic antioxidant system of Aroclor 1254 exposed rats. METHODS: The rats were injected Aroclor 1254 at a dose of 2 mg/kg bw/day intraperitoneally for 30 days. One group of rats received vitamin C (100 mg/kg bw/day) orally simultaneously with Aroclor 1254 for 30 days. Twenty-four hours after last treatment, the animals were killed and hypothalamic region was separated from brain tissue. Enzymatic and non-enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and vitamin C were estimated. Hydrogen peroxide (H(2)O(2)), lipid peroxidation (LPO) and acetylcholine esterase (AchE) activity were determined. Serum gonadotropins such as luteinizing hormone (LH) and follicle stimulating hormone (FSH) were also assayed. RESULTS: Activities of SOD, CAT, GPx, GR, AchE and the concentration of vitamin C were decreased while an increase in H(2)O(2) and LPO were observed in hypothalamus of PCB treated animals. LH and FSH concentrations were also decreased in serum of PCB exposed animals. Vitamin C administration retrieved all the parameters significantly except serum hormonal profiles. CONCLUSION: PCB induces oxidative stress in hypothalamus by decreasing the activities of antioxidant enzymes, which can be protected by vitamin C treatment.

Acetylcholinesterase↗
PubMed2005

Theoretical studies of UO2(H2O)n(2+), NpO2(H2O)n(+), and PuO2(H2O)n(2+) complexes (n=4-6) in aqueous solution and gas phase.

Extensive ab initio calculations both in gas phase and solution have been carried out to study the equilibrium structure, vibrational frequencies, and bonding characteristics of various actinyl (UO2(2+), NpO2(+), and PuO2(2+)) and their hydrated forms, AnO2(H2O)n(z+) (n=4, 5, and 6). Bulk solvent effects were studied using a continuum method. The geometries were fully optimized at the coupled-cluster singles + doubles (CCSD), density-functional theory (DFT), and Møller-Plesset (MP2) level of theories. In addition vibrational frequencies have been obtained at the CCSD as well as MP2/DFT levels. The results show that both the short-range and long-range solvent effects are important. The combined discrete-continuum model, in which the ionic solute and the solvent molecules in the first and second solvation shells are treated quantum mechanically while the solvent is simulated by a continuum model, can predict accurately the bonding characteristics. Moreover, our values of solvation free energies suggest that five- and six-coordinations are equally preferred for UO2(2+), and five-coordinated species are preferred for NpO2(+) and PuO2(2+). On the basis of combined quantum-chemical and continuum treatments of the hydrated complexes, we are able to determine the optimal cavity radii for the solvation models. The coupled-cluster computations with large basis sets were employed for the vibrational spectra and equilibrium geometries both of which compare quite favorably with experiment. Our most accurate computations reveal that both five- and six-coordination complexes are important for these species.

Journal Article↗
PubMed2005

Theoretical characterization of the low-lying electronic states of NbC.

We have studied the potential-energy curves and the spectroscopic constants of the ground and low-lying excited states of NbC by employing the complete active space self-consistent field method with relativistic effective core potentials followed by multireference configuration-interaction calculations. We have identified 23 low-lying electronic states of NbC with different spin multiplicities and spatial symmetries within 40,000 cm(-1). At the multireference single and double configuration interaction level of theory the 2sigma+ and 2delta states are nearly degenerated, with the 2delta state located 187 cm(-1) lower than the 2sigma+ state. The estimated spin-orbit splitting for the 2delta state results in a 2delta(3/2) ground state and A 2sigma+ which is placed 650 cm(-1) above the ground state, in reasonable agreement with the experimental result, 831 cm(-1). Our computed spectroscopic constants are in good agreement with experimental values although our results differ from those of a previous density-functional investigation of the excited states of NbC, mainly due to the strong multiconfigurational character of NbC. In the present work we have not only suggested assignments for the observed states but also computed more electronic states that are yet to be observed experimentally.

Journal Article↗
PubMed2005

Recruitment of beta-2-glycoprotein 1 to cell surfaces in extrinsic and intrinsic apoptosis.

Apoptotic cells and phagocytes have developed a diverse array of distinct ligand-receptor systems that drive the recognition and uptake of dying cells. Phagocytes recognize apoptotic cells either directly, by binding to specific ligands at their cell surface, or indirectly, by binding to bridging proteins that bind these ligands. Previous observations showed that the plasma bridging protein beta2GP1, binds PS containing vesicles, and enhances their binding and engulfment by phagocytes in vitro. In this study we show that apoptotic cells injected intravenously and intraperitonealy into syngeneic mice recruited the PS binding protein, beta2GP1. Examination of peritoneal exudates and spleen thin sections showed that only the injected apoptotic cells picked up endogenous beta2GP1. Recovery of cells from the peritoneum showed that apoptotic cells bearing beta2GP1 were clustered around host peritoneal phagocytes. In addition, tissue sections from mice injected with Fas antibody showed colocalization of beta2GP1 with TUNEL-positive apoptotic cells. These results provide evidence that endogenous beta2GP1 binds apoptotic cells in vivo, suggesting that the protein plays an important physiologic role in the recognition of dying cells.

Animals↗
PubMed2005

Effects of streptozotocin-diabetes and insulin replacement on the epididymis of prepubertal rats: histological and histomorphometric studies.

The present study evaluates the effects of streptozotocin (STZ)-induced diabetes and insulin replacement on the histoarchitecture of caput, corpus, and caudal epididymides during the critical period of sexual maturation in rats. Prepubertal male Wistar rats (40 days old) were made diabetic by a single injection of STZ (120 mg/kg body weight, intraperitoneally). To one set of diabetic rats, insulin was replaced daily at a dose of 3 U/100g body weight, subcutaneously in two equally divided doses at 8:00 a.m. and 6:00 p.m. All the rats were killed on the 61st day of postnatal life. STZ-diabetes reduced the body weight and also caused regression of epididymis, leading to a decrease in the absolute weight of caput, corpus, and caudal regions. Histological studies also revealed a considerable reduction in the size of the tubule and lumen of these segments with an increase in interstitial stroma. Because of shrinkage of tubules, principal cells were packed tightly with clumping of nuclei. Stereological studies support atrophic changes in the caput, corpus, and caudal epididymides by reduction in tubular diameter, volume, and surface density. The epididymal lumen of STZ-treated rats was totally devoid of spermatozoa. These findings emphasize the detrimental effects of diabetes on the maintenance and establishment of fully differentiated epididymal epithelium during sexual maturation. Insulin replacement was only able to prevent the adverse effects of diabetes on certain parameters and this response was region-specific.

Animals↗
PubMed2005

Effects of gamma radiation on luteinizing hormone (LH) receptor expression, signal transduction and steroidogenesis in cultured rat Leydig cells.

PURPOSE: To investigate the dose-dependent effects of gamma radiation on rat Leydig cell luteinizing hormone (LH) receptor expression, signal transduction and steroidogenesis. MATERIALS AND METHODS: Leydig cells isolated from testicles of adult male albino rats were cultured and exposed to different doses (2, 4, 6, 8 and 10 Gy) of fractioned gamma radiation for three days. Normal as well as irradiated cells were used for the quantification of cell surface LH receptor or LH/cyclic adenosine monophosphate (cAMP) stimulation test or total ribonucleic acid (RNA) isolation to study the LH receptor messenger RNA (mRNA) expression by reverse transcriptase polymerase chain reaction (RT-PCR). RESULTS: Radiation was found to have dose-dependent effects on rat Leydig cell surface LH receptor, basal and LH-stimulated cAMP production, basal, LH and cAMP-stimulated steroidogenesis. Lower doses (2 and 4 Gy) of radiation did not induce any change, whereas higher doses (6, 8 and 10 Gy) of radiation exposure diminished the above said parameters significantly. In spite of the low level of cell surface LH receptors following higher doses of radiation exposure, its mRNA level was not altered under any dose level. CONCLUSION: From these observations, it is concluded that gamma radiation has dose-dependent inhibitory effects on Leydig cell LH signal transduction and steroidogenesis. Decreased cell surface LH receptor following higher doses of radiation exposure is not coupled with altered LH receptor mRNA level.

Animals↗
PubMed2005

Impact of polychlorinated biphenyl Aroclor 1254 on testicular antioxidant system in adult rats.

To clarify the reproductive toxicity of polychlorinated biphenyl compounds through determination of testicular lipid peroxidation, reactive oxygen species and enzymatic and non-enzymatic antioxidants in rats exposed to Aroclor 1254. Adult male rats were administered Aroclor 1254 at a dose of 2 mg/kg per day ip for 30 days. The rats were sacrificed 24 hours after last dosing and the serum and other tissues collected and processed for relevant determinations. The body weight and the weights of the testis, epididymis, ventral prostate and seminal vesicle and the serum testosterone and estradiol were significantly decreased in Aroclor 1254 treated rats. The testicular lipid peroxidation, hydrogen peroxide and hydroxyl radical were significantly elevated whereas, testicular antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST) and glutathione reductase (GR) were significantly decreased. The non-enzymatic antioxidants, vitamin C and vitamin E, were also decreased. These results suggest that Aroclor 1254 induces an increase in the lipid peroxidation, hydrogen peroxide and hydroxyl radical and diminish in the antioxidant defense system in rats, indicating that the free radical-dependent mechanism may play an important role in the testicular toxicity of polychlorinated biphenyls.

Animals↗
PubMed2004

Theoretical study of the electronic states of Nb4, Nb5 clusters and their anions (Nb4-,Nb5-).

Geometries and energy separations of the various low-lying electronic states of Nb(n) and Nb(n) (-) (n=4,5) clusters with various structural arrangements have been investigated. The complete active space multiconfiguration self-consistent field method followed by multireference singles and doubles configuration interaction (MRSDCI) calculations that included up to 52x10(6) configuration spin functions have been used to compute several electronic states of these clusters. The ground states of both Nb(4) ((1)A('), pyramidal) and Nb(4) (-) ((2)B(3g), rhombus) are low-spin states at the MRSDCI level. The ground state of Nb(5) cluster is a doublet with a distorted trigonal bipyramid (DTB) structure. The anionic cluster of Nb(5) has two competitive ground states with singlet and triplet multiplicities (DTB). The low-lying electronic states of these clusters have been found to be distorted due to Jahn-Teller effect. On the basis of the energy separations of our computed electronic states of Nb(4) and Nb(5), we have assigned the observed photoelectron spectrum of Nb(n) (-) (n=4,5) clusters. We have also compared our MRSDCI results with density functional calculations. The electron affinity, ionization potential, dissociation and atomization energies of Nb(4) and Nb(5) have been calculated and the results have been found to be in excellent agreement with the experiment.

Journal Article↗
PubMed2004

Spectroscopic properties of novel aromatic metal clusters: NaM4 (M=Al,Ga,In) and their cations and anions.

The ground- and several excited states of metal aromatic clusters, namely NaM(4) and NaM(4) (+/-) (M=Al,Ga,In) clusters have been investigated by employing complete active-space self-consistent-field followed by multireference singles and doubles configuration interaction computations that included up to 10 million configurations and other methods. The ground states NaM(4) (-) of aromatic anions are found to be symmetric C(4nu) ((1)A(1)) electronic states with ideal square pyramid geometries. While the ground state of NaIn(4) is also predicted to be a symmetric C(4nu) ((2)A(1)) square pyramid, the ground state of the NaAl(4) cluster is found to have a C(2nu) ((2)A(1)) pyramid with a rhombus base, and the ground state of NaGa(4) possesses a C(2nu) ((2)A(1)) pyramid with a rectangle base. In general, these structures exhibit two competing geometries, viz., an ideal C(4nu) structure and a distorted rhomboidal or rectangular pyramid structure (C(2nu)). All of the ground states of the NaM(4) (+) (M=Al,Ga,In) cations are computed to be C(2nu) ((3)A(2)) pyramids with rhombus bases. The equilibrium geometries, vibrational frequencies, dissociation energies, adiabatic ionization potentials, adiabatic electron affinities for the electronic states of NaM(4) (M=Al,Ga,In), and their ions are computed and compared with experimental results and other theoretical calculations. On the basis of our computed excited states energy separations, we have tentatively suggested assignments to the observed X and A states in the anion photoelectron spectra of Al(4)Na(-) reported by Li et al. [X. Li, A. E. Kuznetov, H. F. Zheng, A. I. Boldyrev, and L. S. Wang, Science 291, 859 (2001)]. The X state can be assigned to a C(2nu) ((2)A(1)) rhomboidal pyramid. The A state observed in the anion spectrum is assigned to the first excited state ((2)B(1)) of the neutral NaAl(4) with the C(4nu) symmetry. The assignments of the excited states are consistent with the experimental excitation energies and the previous Green's function-based methods for the vertical transition energy separations between the X and A bands.

Journal Article↗
PubMed2004

Spectroscopic properties and potential energy curves of low-lying electronic states of RuC.

The RuC molecule has been a challenging species due to the open-shell nature of Ru resulting in a large number of low-lying electronic states. We have carried out state-of-the-art calculations using the complete active space multiconfiguration self-consistent field followed by multireference configuration interaction methods that included up to 18 million configurations, in conjunction with relativistic effects. We have computed 29 low-lying electronic states of RuC with different spin multiplicities and spatial symmetries with energy separations less than 38,000 cm(-1). We find two very closely low-lying electronic states for RuC, viz., 1Sigma+ and 3Delta with the 1Sigma+ being stabilized at higher levels of theory. Our computed spectroscopic constants and dipole moments are in good agreement with experiment although we have reported more electronic states than those that have been observed experimentally. Our computations reveal a strongly bound 1Sigma+ state with a large dipole moment which is most likely the experimentally observed ground state and an energetically close 3Delta state with a smaller dipole moment. Overall our computed spectroscopic constants of the excited states with energy separations less than 18,000 cm(-1) agree quite well with those of the corresponding observed states.

Journal Article↗