Browsing by Author "Rahul Singh"

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A binuclear Cu(i) complex as a novel catalyst towards the direct synthesis of N-2-aryl-substituted-1,2,3-triazoles from chalcones
(Royal Society of Chemistry, 2016) Divya Pratap Singh; Bharat Kumar Allam; Rahul Singh; Krishna Nand Singh; Vinod Prasad Singh
A binuclear Cu(i) complex containing a N′,N′-bis{(1H-indol-3-yl)methylene}oxalohydrazide (H2bioh) ligand has been synthesized and characterized. The molecular structures of the synthesized compounds have been determined by single crystal X-ray diffraction. The crystal structures are stabilized by inter- and intra-molecular π-π stacking and C-H⋯π interactions. The Cu(i)-complex has successfully been employed as an efficient catalyst for one-pot operation involving the azide-chalcone click reaction and subsequent arylation has been developed. The complex exhibits excellent catalytic activity with significantly low catalyst loading. The overall process is insensitive to air and moisture and can be manipulated under ambient temperature with operational ease. © 2016 The Royal Society of Chemistry.
A direct metal-free decarboxylative sulfono functionalization (DSF) of cinnamic acids to α,β-unsaturated phenyl sulfones
(American Chemical Society, 2015) Rahul Singh; Bharat Kumar Allam; Neetu Singh; Kumkum Kumari; Satish Kumar Singh; Krishna Nand Singh
A metal-free room temperature decarboxylative cross-coupling between cinnamic acids and arylsulfonyl hydrazides has been realized for the first time for the synthesis of (E)-vinyl sulfones. The scope and versatility of the reaction has been demonstrated by the regio- and stereoselective synthesis of 22 derivatives with diverse structural features. © 2015 American Chemical Society.
A Practical Copper Catalyzed N-Arylation of Amines Using Aryl Triazenes as Aryl Source
(Wiley-Blackwell, 2019) Shiv Chand; Saurabh Kumar; Rahul Singh; Krishna Nand Singh
An efficient copper-catalyzed synthesis of N-arylated amines has been developed via cross-coupling of amines with aryl triazenes. The methodology is endowed with broad substrate scope, high yield, and significant functional group tolerance. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
A practical protocol for the synthesis of bibenzyls: Via C(sp3)-H activation of methyl arenes under metal-free conditions
(Royal Society of Chemistry, 2017) Promod Kumar; Tirumaleswararao Guntreddi; Rahul Singh; Krishna Nand Singh
A variety of bibenzyl derivatives have been synthesized with excellent atom economy via C(sp3)-H-C(sp3)-H coupling of readily available methyl arenes using K2S2O8 under metal-free and environmentally benign conditions. © 2016 the Partner Organisations.
A practical synthesis of aryl sulfones via cross-coupling of sulfonyl hydrazides with aryltriazenes using copper/ionic liquid combination
(Elsevier Ltd, 2018) Anand Kumar Pandey; Saurabh Kumar; Rahul Singh; Krishna Nand Singh
A new and efficient approach adopting copper-catalyzed cross-coupling of sulfonyl hydrazides with aryltriazenes has been developed to synthesize aryl sulfones using Brønsted acidic ionic liquid as promoter under ambient conditions. The process employs stable and easy to handle reacting partners, and is endowed with broad substrate scope. © 2018 Elsevier Ltd
A Prospective Study and Analysis of Ventriculoperitoneal Shunt Surgery: Their Indication and Complication in a Single Tertiary Care Center
(Georg Thieme Verlag, 2022) Barnava Pal; Sambuddha Dhar; Anurag Sahu; Sumita Kumari; Kulwant Singh; Kamalpreet Kaur Bhaikhel; Shrish Nalin; Ashvamedh Singh; Rahul Singh
Background Ventriculoperitoneal (VP) shunt insertion is routinely performed for the treatment of hydrocephalus due to different indications like congenital, infective, tumor, posttraumatic, and normal pressure hydrocephalus (NPH). A lot of common and rare complications following this procedure have been reported. Objectives To analyze the clinical profile, indications, anesthetic, and postoperative complications for VP shunt surgery in our center. Materials and Methods This prospective clinical review study was conducted in the Department of Neurosurgery, Institute of Medical Sciences, Banaras Hindu University, Varanasi, between October 2018 to January 2020 and included 454 cases of hydrocephalus who underwent VP shunt surgery. The data was compiled and analyzed. Results A total of 454 patients with male predominance were studied. Pediatric and adolescent patients were 48.9% (222/454). Obstructive hydrocephalus due to tumors was the etiology of 48.7% (221/454) cases. The incidence of overall shunt complications was 9.7% (44/454), of which obstruction and infection was 5.9% (27/454) and 3.1% (14/454), respectively. Factors associated with increased shunt complications include redo and infective etiology and cases having higher protein in perioperative cerebrospinal fluid (CSF) analysis. Neuronavigation, antibiotic-impregnated shunt and biventricular shunt are associated with lower complications. Conclusion Obstructive hydrocephalus due to tumors happened to be the most common cause of VP shunt, and shunt obstruction is most common complication, especially in infective and redo cases. © 2022 Thieme Medical Publishers, Inc.. All rights reserved.
AIBN-Initiated Denitrative Cross-Coupling Reactions of β-Nitrostyrenes with Sulfonyl Hydrazides/Disulfides: A Metal-free Approach towards Vinyl Sulfones
(Wiley-VCH Verlag, 2018) Saurabh Kumar; Rahul Singh; Krishna Nand Singh
A practical approach involving denitrative coupling of β-nitrostyrenes and sulfonyl hydrazides/disulfides by AIBN (azobisisobutyronitrile) has been developed to accomplish the synthesis of vinyl sulfones. The method employs easily accessible starting materials, and is endowed with a broad substrate scope and functional group tolerance. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
An efficient and green synthesis of pyrazolophthalazinyl spirooxindoles using task specific ionic liquid
(Scientific Publishers, 2014) Kumkum Kumari; Rahul Singh; Krishna Nand Singh
An environmentally benign approach for the synthesis of pyrazolophthalazinyl spirooxindoles has been developed with the help of a task-specific ionic liquid [DBU][AcOH], which plays the dual role of catalyst as well as reaction medium. The advantages of this method include the use of green reaction conditions, no organic solvent, easy work-up, excellent yields and recyclability of the ionic liquid.
An Efficient Synthesis of 1,2-Diketones by Oxidative Cross-coupling of Alkynes and Aryl Triazenes using Copper Catalysis
(Wiley-Blackwell, 2019) Ramesh Kumar Vishwakarma; Saurabh Kumar; Anup Kumar Sharma; Rahul Singh; Krishna Nand Singh
An efficient and mild approach to 1,2-diketones has been developed via oxidative cross-coupling of alkynes and aryl triazenes using copper catalysis under open atmosphere. The approach is convenient, clean, and offers a wide range of substrate scope and functional group tolerance. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Anomalous Hall effect in Cu doped Bi2Te3 topological insulator
(Institute of Physics Publishing, 2020) Abhishek Singh; Shiv Kumar; Mahima Singh; Prajyoti Singh; Rahul Singh; Vinod K Gangwar; Archana Lakhani; Swapnil Patil; Eike F Schwier; Takeshi Matsumura; K. Shimada; A.K. Ghosh; Sandip Chatterjee
The angle resolved photo-emission spectroscopy (ARPES) study and magneto-transport properties of Bi2CuxTe3-x have been investigated. ARPES study indicates the clear existence of surface states in the as-prepared samples. The estimated bandgap from ARPES is found to be ∼5 meV and 16 meV respectively for x = 0.03 and x = 0.15 samples. Presence of larger Cu concentration (x = 0.15) introduces magnetic ordering. Observed non-linearity in the Hall data is due to the existence of anomalous Hall effect which can be attributed to the 2D transport. The observed magneto-transport features might be related to the surface carriers which is confirmed by ARPES study. © 2020 IOP Publishing Ltd.
Bayes Estimator of Generalized-Exponential parameters under Linex loss function using Lindley's approximation
(Ubiquity Press Ltd, 2008) Rahul Singh; Sanjay Kumar Singh; Umesh Singh; Gyan Prakash Singh
In this paper, we have obtained the Bayes Estimator of Generalized- Exponential scale and shape parameter using Lindley 's approximation (L-approximation) under asymmetric loss functions. The proposed estimators have been compared with the corresponding MLE for their risks based on simulated samples from the Generalized-Exponential distribution.
Clinical, operative, and outcome analysis of giant extradural hematoma: A retrospective study in tertiary care center
(Scientific Scholar, 2020) Rahul Singh; Anurag Sahu; Kulwant Singh; Ravi Shankar Prasad; Nityanand Pandey
Background: This study is aimed to find a critical volume of operated giant or massive extradural hematoma (EDH) that affects outcome significantly and analyze them with respect to their clinical, surgical, and outcome perspective. Methods: This retrospective study includes 253 patients operated for EDH in emergency in the Department of Neurosurgery of IMS BHU, Varanasi, India, a tertiary care center, between August 1, 2018, and November 1, 2019. Giant EDH critical volume was evaluated. Twenty-nine patients with giant EDH with clot volume ≥ 80 ml were further analyzed for clinical, surgical, and outcome predictive factors. Statistical analysis was done using Prism GraphPad ver. 8.0.0. P value was taken at 0.05. Results: Dichotomized group analysis with Glasgow Outcome Score (GOS) 4-5 versus GOS 1-3 for testing clot volume revealed significance difference with P < 0.001. Mean volume of GOS 1-3 came out to be 79.68 ml. Hence, we took clot volume >80 ml for further analysis. The most common age group was 20-40 (55.17%). M2 (31.03%) was the most common best motor response in operated giant EDH cases. Most of them were having severe (79.31%) head injury. Glasgow Coma Scale (GCS) at admission (P < 0.0001), pupillary changes (P = 0.0032), and best motor response (P < 0.0001) was significantly (P < 0.05) associated with outcome following surgery for giant EDH. Conclusion: Giant EDH with volume ≥ 80 ml is associated with poorer outcome. GCS at admission, pupillary changes, and best motor response is predictors for surgical outcome of giant EDH. © 2020 Published by Scientific Scholar on behalf of Surgical Neurology International
Clinical, Surgical and Outcome Predictive Factor Analysis of Operated Acute Subdural Hematoma Cases: A Retrospective Study of 114 Operated Cases at Tertiary Centre
(Georg Thieme Verlag, 2022) Rahul Singh; Ravi Shankar Prasad; Kulwant Singh; Anurag Sahu; Nityanand Pandey
Objective To analyze clinical, surgical and outcome predictive factors of operated acute subdural hematoma (SDH) cases for prognostication and surgical outcome prediction. Material and Methods This retrospective study includes 114 patients operated for acute SDH in the Department of Neurosurgery of IMS BHU, Varanasi, India, a tertiary care center, between 1 August 2018 and 1 November 2019. Each patient was evaluated for age, sex, mode of injury, localization of hematoma, clinical presentation, comorbidity, severity of injury, best motor response, CT findings, and Glasgow outcome scale (GOS) at discharge. The outcome was also evaluated by further making a dichotomized group using GOS in death/dependent (1-3) versus independent (4-5). Statistical tests were done using the GraphPad Prism version 8.3.0. Results The most common age group operated upon in this study was the 40 to 60 years age group (n = 45, 39.48%). Males were 78% with male to female ratio of 3.56:1. The most common clinical presentation was altered sensorium (98.25%). The most common comorbidity was hypertension (n = 32, 28.07%). GCS at admission, severity of injury, pupillary changes, and best motor response (p < 0.0001) were significantly associated with surgical outcome. Conclusion GCS at admission, severity of injury, pupillary changes, and best motor response were significantly (p < 0.05) associated with surgical outcome. Age and gender of patients were not found to be significantly associated. © 2022 Thieme Medical Publishers, Inc.. All rights reserved.
Convenient MW-assisted synthesis of unsymmetrical sulfides using sulfonyl hydrazides as aryl thiol surrogate
(American Chemical Society, 2013) Neetu Singh; Rahul Singh; Dushyant S. Raghuvanshi; Krishna Nand Singh
An efficient synthesis of unsymmetrical sulfides has been achieved via the cross-coupling reaction of aryl/het-aryl/benzyl halides with stable and easily workable sulfonyl hydrazides as thiol substitutes by means of [DBU][HOAc] and CuI under microwave irradiation. © 2013 American Chemical Society.
Cooperatively assisted N-arylation using organic ionic base-Brønsted acid combination under controlled microwave heating
(2013) Rahul Singh; Bharat Kumar Allam; Dushyant Singh Raghuvanshi; Krishna Nand Singh
A new synthetic strategy is developed for the construction of C-N bond through the assistance of Brønsted acid/[DBU][HOAc] without adding any metal catalyst. This is the first efficient SNAr methodology utilizing fluoro, chloro, bromo, and iodoarenes as coupling partners, which offers excellent yield up to 94% within a very short time. © 2012 Elsevier Ltd. All rights reserved.
Decarboxylative Arylation of α,β-Unsaturated Carboxylic Acids Using Aryl Triazenes by Copper/Ionic Liquid Combination in PEG-400
(Wiley-VCH Verlag, 2018) Saurabh Kumar; Anand Kumar Pandey; Rahul Singh; Krishna Nand Singh
A practical method for the construction of stilbene derivatives has been developed via catalytic cross-coupling of cinnamic acids with aryl triazenes. The methodology offers high stereoselectivity and is endowed with broad substrate scope, high yield, and significant functional group tolerance. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Development of novel iron-regulated Pasteurella multocida B: 2 bacterin and refinement of vaccine quality in terms of minimum variation in particle size and distribution vis-a-vis critical level of iron in media
(Academic Press, 2020) Rajat Varshney; Ritu Varshney; Vinod Kumar Chaturvedi; Mayank Rawat; M. Saminathan; Vidya Singh; Rahul Singh; Monalisa Sahoo; Praveen Kumar Gupta
To enhance the qualitative bacterial biomass per unit of media and to overcome the limitations of the existing haemorrhagic septicaemia (HS) vaccines, a comprehensive study was undertaken encompassing the role of iron on the bacterial biomass of Pasteurella multocida B: 2 to vaccine development. Trypsin digested hydrochloric acid-treated sheep blood (THSB) as a novel iron rich supplement had been devised for the first time for augmenting the qualitative bacterial biomass per unit of media which was evident with growth kinetic study. The higher recovery of iron from THSB became evident via atomic absorbance spectrophotometry. The critical level of iron in the media as well as mode of iron supplementation showed a major impact on the outer membrane protein profile of P. multocida B:2 and variation in droplet size and particle-size distribution of formulated vaccine. Immune response study against iron-regulated bacterin adjuvanted with aluminum hydroxide gel in mouse model showed that 3% THSB supplementation of casein sucrose yeast (CSY) not only augmented the growth of P. multocida B:2 significantly but conferred highest pre-challenged ELISA IgG titer and protection against pasteurellosis. Thus, THSB supplementation of CSY can resolve existing up-scaling and immunogenic potential problems of HS vaccine production. © 2020
Effect of chemical pressure at the boundary of mott insulator to itinerant electron limit transition in spinel vanadates
(American Scientific Publishers, 2015) P. Shahi; A. Kumar; Rahul Singh; Ripandeep Singh; P.U. Sastry; A. Das; Amish G. Joshi; A.K. Ghosh; A. Banerjee; Sandip Chatterjee
The effect of chemical pressure on the structural, transport, magnetic and electronic properties of ZnV2O4 has been investigated by doping Mn and Co onto the Zn sites of ZnV2O4. With Mn doping the V-V distance increases and with Co doping it decreases. The resistivity and thermoelectric power data indicate that, as the V-V distance decreases, the system moves towards quantum phase transition. The transport data also indicate that the conduction is due to small polaron hopping. The chemical pressure shows a non-monotonous behaviour of charge gap and activation energy. On the other hand, when Ti is doped on the V-site of ZnV2O4, the metal-metal distance decreases and, at the same time, TN also increases. © 2015 by American Scientific Publishers.
Effect of Pr- and Nd-doping on structural, dielectric, and magnetic properties of multiferroic Bi0.8La0.2Fe 0.9Mn0.1O3
(American Institute of Physics Inc., 2014) Rahul Singh; G.D. Dwivedi; P. Shahi; D. Kumar; Om Prakash; A.K. Ghosh; Sandip Chatterjee
Bi0.8La0.15RE0.05Fe0.9Mn 0.1O3 (where RE = Pr and Nd) have been prepared via conventional solid state route. The Rietveld refinement of X-ray diffraction patterns shows that both systems crystallize in orthorhombic Pnma space group. Raman modes observed for these two systems indicate that both systems are very close to orthorhombic Pnma structure. Appearance of prominent A1-3 and weak E-2 modes in Bi0.8La0.15Nd0.05Fe 0.9Mn0.1O3 indicate the presence of chemically more active Bi-O covalent bonds (which favors stereochemical activity of Bi lone pair electrons) in comparison to Bi0.8La0.15Pr 0.05Fe0.9Mn0.1O3. Moreover, Bi 0.8La0.15Nd0.05Fe0.9Mn 0.1O3 system shows higher dielectric constant, low dielectric loss, and higher magnetization value in comparison to Bi 0.8La0.15Pr0.05Fe0.9Mn 0.1O3 system. Ferroelectric transition temperature decreases to 460 °C for both systems in comparison to 710 °C of Bi 0.8La0.2Fe0.9Mn0.1O3. The improved dielectric and magnetic response suggests Bi0.8La 0.15Nd0.05Fe0.9Mn0.1O3 a better multiferroic system than Bi0.8La0.15Pr 0.05Fe0.9Mn0.1O3. © 2014 AIP Publishing LLC.
Elemental sulfur mediated synthesis of benzoxazoles, benzothiazoles and quinoxalines: Via decarboxylative coupling of 2-hydroxy/mercapto/amino-anilines with cinnamic acids
(Royal Society of Chemistry, 2016) Tirumaleswararao Guntreddi; Rajeshwer Vanjari; Saurabh Kumar; Rahul Singh; Neetu Singh; Promod Kumar; Krishna Nand Singh
An easy and practical method has been developed for the synthesis of 2-benzylbenzoxazoles and 2-benzylbenzothiazoles using sulfur mediated decarboxylative coupling of cinnamic acids with 2-hydroxyanilines and 2-mercaptoanilines respectively under metal- and solvent-free conditions. However, the reaction of 2-aminoanilines with cinnamic acids leads to the formation of 2-arylquinoxalines under the same set of reaction conditions. The transformation is versatile and compatible with a number of functional groups. © 2016 The Royal Society of Chemistry.