Browsing by Author "P.K. Shukla"

Now showing 1 - 20 of 56

A curious observation of Pauli-Blocking in MoS2-quantum dots/graphene hybrid system
(American Institute of Physics Inc., 2018) Amulya Nemoori; Himanshu Mishra; Vijay Kumar Singh; P.K. Shukla; Anchal Srivastava; Amritanshu Pandey
In this study, Pauli-Blocking has been observed in a 0D/2D MoS2 quantum dots/graphene (MoS2-QDs/graphene) hybrid system. For the observation of room temperature Pauli-Blocking in the 0D/2D system, a photodetector device based on n-type MoS2-QDs and CVD grown graphene has been fabricated using a facile and lithography free technique. The current-voltage characteristics of the device have been performed at room temperature. The fabricated device shows a negative response under visible light (λ ∼ 400 to 700 nm) illumination. The dark to photo current ratio of the device shows variation up to two orders of magnitude. This negative response, which results decrease in current under visible light illumination, may be attributed to the Pauli-Blocking due to high absorbance of photon energy in visible light range. Furthermore, it is believed that the present study may provide an insight into understanding the Pauli-Blocking in 0D/2D hybrid system at room temperature. © 2018 Author(s).
A possible mechanism for the emergence of an additional band gap due to a Ti-O-C bond in the TiO2-graphene hybrid system for enhanced photodegradation of methylene blue under visible light
(Royal Society of Chemistry, 2014) Sima Umrao; Shiju Abraham; Frank Theil; Shobhit Pandey; Valerian Ciobota; P.K. Shukla; Caroline J. Rupp; Sudip Chakraborty; Rajeev Ahuja; Jürgen Popp; Benjamin Dietzek; Anchal Srivastava
Here we report the experimental and theoretical study of two TiO2-graphene oxide (TG) and TiO2-reduced graphene oxide (TR) composites synthesized by a facile and ecological route, for enhanced visible light (∼470 nm) photocatalytic degradation of Methylene Blue (MB) (99% efficiency), with high rate constant values (1800% over bare TiO2). TG couples TiO2 nanopowder with Graphene Oxide (GO) while TR couples it with reduced graphene oxide (RGO). The present study, unlike previous reports, discusses never-before-reported double absorption edges obtained for both TG (3.51 eV and 2.51 eV) and TR (3.42 eV and 2.39 eV) composites, which represents the reason behind feasible visible light (2.56 eV) induced photocatalysis. TiO2 domains in the composites dominate the higher band edge, while GO/RGO domains explain the lower band edge. Formation of Ti-O-C bonds in both TG and TR drives the shifting upwards of the valence band edge and reduction in band gap. Further, these bonds provide a conductive pathway for charge carriers from TiO2 nanopowder to the degraded species via the GO/RGO matrix, resulting in decreased charge carrier recombination in TiO2 and enhanced efficiency. To attest that the developed theory is correct, density function theory (DFT) calculations were performed. DFT obtained energetics and electronic structures support experimental findings by demonstrating the role of the Ti-O-C bond, which results in double band edge phenomenon in composites. Finally, the mechanism behind MB degradation is discussed comprehensively and the effect of the weight percent of GO/RGO in the composite on the rate constant and photodegradation efficiency has been studied experimentally and explained by developing analytical equations. © The Royal Society of Chemistry 2014.
A quantum chemical study of reactions of DNA bases with sulphur mustard: A chemical warfare agent
(2010) P.K. Shukla; P.C. Mishra
Reactions of the sulphonium ion of sulphur mustard (SM+1) at the N7, N3 and O6 sites of guanine, N7, N3 and N1 sites of adenine, O2 and N3 sites of cytosine and O2 and O4 sites of thymine were studied theoretically in gas phase and aqueous media employing density functional theory (DFT) and second order Møller-Plesset perturbation (MP2) theory. The B3LYP, B3PW91 and B1B95 functionals of DFT and the 6-31+G* and AUG-cc-pVDZ basis sets were used in the calculations. Basis set superposition error was treated using the counterpoise method by single point energy calculations at the B3LYP/6-31+G* level in gas phase. The present study explains the mechanism of alkylation of the DNA bases and shows that SM+1 would form stable adducts at the endocyclic nitrogen sites of the DNA bases, and at the O6 site of guanine and the O2 site of cytosine. Formation of adducts at the N7 site of guanine and N3 site of adenine are found to be most favored and next most favored respectively, which agrees with experimental observations. © Springer-Verlag 2009.
A quantum theoretical study of reactions of methyldiazonium ion with DNA base pairs
(2011) P.K. Shukla; Vinay Ganapathy; P.C. Mishra
Methylation of the DNA bases in the Watson-Crick GC and AT base pairs by the methyldiazonium ion was investigated employing density functional and second order Møller-Plesset (MP2) perturbation theories. Methylation at the N3, N7 and O6 sites of guanine, N1, N3 and N7 sites of adenine, O2 and N3 sites of cytosine and the O2 and O4 sites of thymine were considered. The computed reactivities for methylation follow the order N7(guanine) > N3(adenine) > O6(guanine) which is in agreement with experiment. The base pairing in DNA is found to play a significant role with regard to reactivities of the different sites. © 2011 Elsevier B.V. All rights reserved.
A simple device for performing fine needle aspiration cytology.
(1993) P.K. Shukla
A Simple reusable device has been fabricated from the barrel of the ten ml plastic disposable syringe to hold the piston of 20 ml disposable syringe for Fine Needle Aspiration Cytology (FNAC), in position of full retraction so as to produce continuous negative pressure inside. The device has been found very satisfactory inexpensive and has special relevance to situations where the standard syringe holder is not available.
Aspergillosis of the maxillary sinus
(Springer India, 1998) M.K. Agarwal; P.K. Shukla
A rare case of aspergillosis of the maxillary sinus is reported. Surgical excision including the lining of the infected sinus is the preferred method of treatment. Antiimmunotherapy does not seem to affect the prognosis of this disease.
Binding of urea and thiourea with a barbiturate derivative: Experimental and theoretical approach
(2010) Namrata Dixit; P.K. Shukla; P.C. Mishra; Lallan Mishra; Herbert W. Roesky
A barbiturate derivative [1,5-dihydro-5-[5-pyrimidine-2,4(1H,3H)-dionyl]- 2H-chromeno[2,3-d] pyrimidine- 2,4(3H)-dione)] (L1) possesses functionalities complementary to amide and thioamide. Hence its binding with urea and thiourea, is monitored using UV-vis and fluorescence titrations as well as isothermal titration calorimetry (ITC) study. Theoretical studies on hydrogen-bonded complexes of Ll-urea and Ll-thiourea in the gas phase, aqueous, and DMSO medium are carried out using density functional theory (DFT) at the B3LYP/6-31G** level. The theoretical calculations support the experimental results. © 2010 American Chemical Society.
Calvarial plasmacytoma. A case report
(1988) S. Mohanty; S.K. Gupta; P.K. Shukla; S.K. Gupta
[No abstract available]
Catalytic involvement of CO2 in the mutagenesis caused by reactions of ONOO- with guanine
(American Chemical Society, 2008) P.K. Shukla; P.C. Mishra
The catalytic role of CO2 in reactions of ONOO- with guanine, leading to the formation of the mutagenic species 8-oxoguanine (8-oxoG) and 8-nitroguanine anion (8-nitroG-), was investigated by considering the reactions of nitrosoperoxycarbonate anion (ONOOCO 2-), an adduct of ONOO- and CO2, with guanine at the B3LYP/6-31G** and B3LYP/AUG-cc-pVDZ levels of density functional theory in gas phase. In order to study bulk solvent effect, single-point energy calculations in aqueous media were carried out for all the species occurring in the reactions at the B3LYP/AUG-cc-pVDZ level of theory, by use of the polarizable continuum model (PCM). Vibrational frequency analysis was performed, and zero-point-energy (ZPE)-corrected total energies and Gibbs free energy changes at 298.15 K were obtained. The genuineness of the calculated transition states was confirmed by visually examining the vibrational modes and also by intrinsic reaction coordinate (IRC) calculations. The reaction between ONOOCO2- and guanine occurring through four different mechanisms leads to the formation of 8-oxoG or its anion, while the reaction between the same two species occurring through a different scheme leads to the formation of 8-nitroG-. It has been shown that the presence of a water molecule along with ONOOCO2- would not affect the reaction mechanisms significantly. Structures of the reactant complexes, product complexes and barrier energies involved in the reactions reveal that CO 2 acts as a catalyst for the reaction between ONOO- and guanine. The cause of the catalytic action of CO2 is mainly due to intermediacy of the CO3 radical anion and NO2 radical into which ONOOCO2- is fragmented while reacting with guanine. The relative stabilities of the different product complexes suggest that the mutation caused by ONOO- in the presence of CO2 would mainly involve 8-oxoG. © 2008 American Chemical Society.
Combined treatment modalities for intracranial tumours
(1978) B. Sanyal; G.C. Pant; K. Subrahmaniyam; K. Sahni; M.S. Agarwal; S. Mohanty; C.J. Rao; P.K. Shukla
[No abstract available]
Comparative aspects of a metal loaded triangular waveguide with uniform and non-uniform distribution of Goell's matching points
(IETE, 1995) P.K. Shukla; P. Khastgir; S.P. Ojha; P.K. Choudhury
Using Goell's point matching method, a numerical analysis has been made of a Metal loaded Triangular Waveguide (MTW) with a non-uniform distribution of matching points, some of which are crowded near the corners of the triangle, and the results are compared with those reported earlier for an MTW with the matching points distributed in a uniform manner. An interesting aspect is observed that, as expected, a redistribution of the matching points without changing the total number of such points leads to a significantly different and better approximation to the modal characteristics than those obtained through a uniform distribution of points.
Comparative photoelectrochemical study of PEC solar cell fabricated with n-TiO2 photoelectrodes at different temperatures and under different oxygen flow rates
(2006) P.R. Mishra; P.K. Shukla; O.N. Srivastava
Photoelectrochemical splitting of water induced by solar energy for hydrogen production has been studied in the present investigation. PEC solar cell was fabricated with n-TiO2 photoelectrodes synthesized at different oxidation temperatures e.g. 700°C, 750°C, 800°C and 850°C under oxygen flow rate 200 ml/min, 350 ml/min and 500 ml/min. The optimum oxygen flow rate for all the temperatures was found to be 350 ml/min. This is therefore kept invariant for synthesis of electrodes at different temperatures. The photoelectrochemical characterization of the PEC cell was done in the three-electrode configuration, i.e Ti/n-TiO2/1M-NaOH/Pt. It has been observed that the optimum values of the PEC solar cell parameters are exhibited by the solar cell employing the photoelectrodes prepared at ∼750°C. The XRD and SEM explorations revealed that the TiO2 prepared at ∼750°C is in the nanometric range (∼100-150 nm). The TiO2 films formed at this temperature has been found to exhibit optimum PEC solar cell parameters. The PEC parameters, like photocurrent density, photoconversion efficiency and hydrogen production rate, with this photoelectrode correspond to 0.93 mA/cm2, 0.472% and 4.00 l/hm 2 respectively.
DNA lesions caused by ROS and RNOS: A review of interactions and reactions involving guanine
(Springer Netherlands, 2010) P.K. Shukla; P.C. Mishra
DNA is constantly attacked by a large number of endogenous and exogenous reactive oxygen species (ROS), reactive nitrogen oxide species (RNOS), and alkylating agents which produce a wide variety of modifications of its constituents, particularly the bases. Some of these modifications (lesions) are hazardous to normal cell functioning, and are implicated in several lethal conditions including chronic inflammatory diseases, atherosclerosis, aging, mutation, cancer, and neurodegenerative disorders, such as the Alzheimer's and Parkinson's diseases. ROS and RNOS are present abundantly in living cells, and can oxidize and/or nitrate almost all the classes of biomolecules including DNA. Different ROS and RNOS primarily react with guanine in DNA to form 8-oxoguanine (8-oxoG) and 8-nitroguanine (8-nitroG) along with other mutagenic products. 8-OxoG readily mispairs with adenine during DNA replication to cause GC → AT transversion mutation. 8-OxoG and 8-nitroG are considered to be highly potent initiators of mutation and cancer. Reactions of guanine and/or imidazole, the latter taken as a model for the five-membered ring of guanine, with different ROS and RNOS including the OHċ radical, H2O 2, H2O3, ONOO-, ONOOCO 2 -, HOCl, and NO2Cl, have been studied using quantum chemical methods. The present review brings out the main, interesting features of the results obtained in such studies. © 2010 Springer Science+Business Media B.V.
Effects of diameter, length, chirality and defects on the scavenging action of single-walled carbon nanotubes for OH radicals: A quantum computational study
(2010) P.K. Shukla; P.C. Mishra
Binding of an OH radical at the outer surfaces of the open-ended pristine armchair (5, 5), (7, 7) single-walled carbon nanotubes of varying lengths, zigzag (9, 0), (10, 0) tubes, and Stone-Wales and single vacancy defected (5, 5) tubes was investigated theoretically. Binding of two OH radicals with a zigzag (10, 0) nanotube was also investigated. The semiempirical PM6 method was used for geometry optimization which was followed by single-point energy calculations at B3LYP/6-31G(d,p) level of density functional theory. Binding energies of the adducts of armchair nanotubes with an OH radical each were found to decrease with increase in diameter, this effect being more pronounced for longer tubes. Semi-conducting zigzag (10, 0) tube was found to be a better OH radical scavenger than the metallic armchair (5, 5) and zigzag (9, 0) tubes. Stone-Wales and single vacancy defected armchair tubes were found to be less and more reactive respectively towards an OH radical than the corresponding pristine tubes. © 2010 Elsevier B.V. All rights reserved.
Familial gliomas : A case report
(1999) A.R. Bhatt; S. Mohanty; V. Sharma; P.K. Shukla
Two non-twin brothers were found to have intracranial malignant neoplasms. The age of presentation was third and fourth decade but the onset was simultaneous, at the same time. Diagnosis in each of them was made by computed tomography and confirmed by histopathology. Elder among them had cellular ependymoma and the younger had oligodendroglioma. Both the brothers received radiotherapy post operatively and were surviving asymptomatically without any neurological deficit, leading active life as police constable, 12 months after surgical treatment.
Giardiasis in adults. Studies on jejunum and immunoglobulins
(1979) J.P. Gupta; K.S. Nampoothiry; P.C. Sen; P.K. Shukla; S.N. Rao; G.C. Pant; H.S. Bajpai
In India, parasitic infestations form the major public health hazard and hookworm and Giardia lamblia form the major gut parasitic infestation. In thirty-four adult patients with proven excretion of Cr51 albumin, serum protein, serum immunoglobulin and biopsies of the jejunal mucosa were studied. The present study showed mild to moderate steatorrhoea in 27% and carbohydrate malabsorption in 31% of the cases. There was no excessive gut protein loss and serum proteins were normal in most of the cases. Jejunal mucosal abnormalities were observed in 40% of the cases. Serum IgA and IgG were significantly high.
Glycosylated hemoglobin and diabetic retinopathy.
(1991) R. Singh; V. Prakash; P.K. Shukla; S. Gautam; O.P. Maurya
Estimation of glycosylated hemoglobin (HbA1c) levels by modified Fluckinger and Winterhalter's method was done in 25 normal persons, 25 diabetic patients without retinopathy, and 25 diabetic patients with retinopathy. The HbA1c values were significantly higher in diabetic patients with or without retinopathy than in the control group (P less than .001). In diabetic patients with retinopathy, the mean value of HbA1c was higher in proliferative retinopathy than in background retinopathy, but statistical analysis showed this was not significant (P greater than .6).
H2O3 as a reactive oxygen species: Formation of 8-oxoguanine from its reaction with guanine
(American Chemical Society, 2007) P.K. Shukla; P.C. Mishra
Reaction of guanine with H2O3 in the absence and presence of a water molecule leading to the formation of 8-oxoguanine (8-oxoG) was investigated. Initial calculations were performed using imidazole (Im) as a model for the five-membered ring of guanine. The reactant, intermediate, and product complexes as well as transition states were obtained in gas phase at the B3LYP/6-31+G* and B3LYP/AUG-cc-pVDZ levels of theory. In all the cases, except for the reactions involving imidazole, single-point energy calculations were performed in gas phase at the MP2/AUG-cc-pVDZ level of theory. Solvation calculations in aqueous media were carried out using the polarizable continuum model (PCM) of the self-consistent reaction field (SCRF) theory. Vibrational frequency analysis and intrinsic reaction coordinate (IRC) calculations were performed to ensure that the transition states connected the reactant and product complexes properly. Zero-point energy (ZPE)-corrected total energies and Gibbs free energies at 298.15 K in gas phase and aqueous media were obtained. When a reaction of H2O3 in place of H2O 2 with guanine is considered, the major barrier energy which is encountered at the first step is almost halved showing that H2O 3 would be much more reactive than H2O2. Considering the reaction schemes investigated here and the observed fact that H2O3 is dissociated easily under ambient conditions, it appears that H2O3 would serve as an effective reactive oxygen species. © 2007 American Chemical Society.
Hepatocellular injury in thermal burns
(1978) P.P. Vaidya; S.K. Roy; P.K. Shukla; R.M. Gupta
Twenty five patients with thermal burns, divided into 2 groups, were evaluated for their liver functions by estimation of certain specific serum enzymes to ascertain the possible mechanism of the clinically inexplicable late deaths. Serum enzyme alterations were evident in all cases suggesting hepatocellular damage, being proportional to the extent and severity of the injury and more profound between the post-burn days 6 to 16, i.e. the 2nd wk. However, no difference was noted in the enzyme levels in fatal burns as against the survivors having a comparable degree of burn-injury. The possible relation of RES depression to hepatocellular necrosis and the final outcome has been emphasized.
Hydrogen atom abstraction reactions of the sugar moiety of 2′-deoxyguanosine with an OH radical: A quantum chemical study
(2011) P.K. Shukla; N. Kumar; P.C. Mishra
Mechanisms of hydrogen atom abstraction reactions of the sugar moiety of 2′-deoxyguanosine with an OH radical were investigated using the B3LYP and BHandHLYP functionals of density functional theory and the second order Møller-Plesset Perturbation (MP2) theory in gas phase and aqueous media. The 6-31+G* and AUG-cc-pVDZ basis sets were used. Gibbs free barrier energies and rate constants of the reactions in aqueous media suggest that an OH radical would abstract the hydrogen atoms of the sugar moiety of 2′-deoxyguanosine in the following order of preference: H5′ ≈ H5″ > H3′ > H4′ > H1′ ≈ H2′ > H2″, the rate constant for H5′ abstraction being 10 3-105 times greater than that for H2″ at the different levels of theory. Relative stabilities of the different deoxyribose radicals are also discussed. The most and least favored hydrogen abstraction reactions found here are in agreement with experimental observation. Copyright © 2010 Wiley Periodicals, Inc.