Browsing by Author "Vijay Kumar"

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A Facile and Simple Strategy for the Synthesis of Label Free Carbon Quantum Dots from the latex of Euphorbia milii and Its Peroxidase-Mimic Activity for the Naked Eye Detection of Glutathione in a Human Blood Serum
(American Chemical Society, 2019) Daraksha Bano; Vijay Kumar; Vikas Kumar Singh; Subhash Chandra; Devendra Kumar Singh; Pradeep Kumar Yadav; Mahe Talat; Syed Hadi Hasan
Herein a green synthetic route has been developed for the synthesis of water-soluble CQDs by facile single-step hydrothermal treatment of latexes of E. milii plant for the first time. This methodology is zero-cost; uses ultrapure water as a green solvent; does not use strong concentrated acid; and avoids the use of post surface passivating agents. The as-prepared CQDs exhibited excellent optical properties, including high QY up to 39.2%, resistance to high salt strength, and long time photostability. Furthermore, the as-prepared CQDs served as an intrinsic peroxidase-mimic activity to catalyze the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) associated with H 2 O 2 , which resulted into a blue-colored reaction with a characteristic absorbance peak at 652 nm. Afterward, the proposed TMB-based oxidation system act as a probe for the detection of GSH and offers the high selectivity relative to the different amino acids and various other interfering agents which can be easily seen with naked eye. The limit of detection (LOD) was found to be 5.3 nM in a linear range 0.02 to 0.1 μM of GSH concentration which showed to be superior under the optimal condition as compared with another probe. To demonstrate the practical feasibility for the GSH detection, the present system was successfully applied on human blood serums with good recovery. © 2018 American Chemical Society.
An actinomycete isolate from solitary wasp mud nest having strong antibacterial activity and kills the Candida cells due to the shrinkage and the cytosolic loss
(Frontiers Media S.A., 2014) Vijay Kumar; Bindu Naik; Omprakash Gusain; Gajraj S. Bisht
An actinomycetes strain designated as MN 2(6) was isolated from the solitary wasp mud nest. The isolate was identified using polyphasic taxonomy. It produced the extensive branched brown substrate and white aerial hyphae that changed into grayish black. The aerial mycelia produced the spiral spore chains with rugose spore surface. The growth was observed between temperature range of 27-37°C, pH 8-10 and below salt concentration of 6% (w/v). The comparative analysis of 16S rRNA gene sequence and phylogenetic relationship showed that strain MN 2(6) lies in clade with Streptomyces hygroscopicus subsp. hygroscopicus NRRL 2387T, Streptomyces sporocinereus NBRC 100766T and Streptomyces demainii NRRL B-1478T with which it shares a 16S rRNA gene sequence similarity of 99.3%. The strain MN 2(6) can be differentiated from type strains based on phenotypic characteristics. The strain MN 2(6) showed most promising activity against Gram-positive, Gram-negative bacteria, acid-fast bacilli and Candida species suggesting broad-spectrum characteristics of the active metabolite. Evaluation of anti-candidal activity of the metabolite of strain MN 2(6) by scanning electron microscopy (SEM) revealed changed external morphology of yeast. It kills the Candida cells due to the shrinkage and the cytosolic loss. However, further studies are required to elucidate the structure of the active metabolite produced by the isolate MN 2(6). © 2014 Kumar, Naik, Gusain and Bisht.
Biosynthesis of silver nanoparticles from the novel strain of Streptomyces Sp. BHUMBU-80 with highly efficient electroanalytical detection of hydrogen peroxide and antibacterial activity
(Elsevier Ltd, 2017) Rajeev Kumar Gupta; Vijay Kumar; Ravi Kumar Gundampati; Manisha Malviya; Syed Hadi Hasan; Medicherla V. Jagannadham
The use of a microbial supernatant has become a potential source for the eco-friendly and rapid synthesis of nanoparticles. In this study, we have targeted to synthesize silver nanoparticles (AgNPs) using extracellular secretion of Streptomyces sp. The strain was successfully isolated from the soil samples and identified as Streptomyces sp. BHUMBU-80 on the basis of morphological, biochemical and Phylogenetic analysis. The synthesized AgNPs was characterized using several modern characterizing techniques such as UV-vis Spectroscopy, FTIR spectroscopy, SEM, EDX spectroscopy, TEM, XRD and XPS. The presence of characteristics SPR band at 450 nm confirmed the synthesis of AgNPs. The FTIR spectra confirmed the involvement of various functional groups present in culture supernatant responsible for the reduction of Ag+ ions into Ag0. SEM and TEM analysis confirmed the presence of spherical AgNPs with an average size of 21 ± 1 nm. The XPS analysis confirmed the presence of two individual peaks which attributed to the Ag 3d3/2 and Ag 3d5/2 binding energies corresponding to the presence of metallic silver. The electrochemical studies of the green synthesized AgNPs using a glassy carbon electrode showed the superior electrocatalytic activity towards the reduction of H2O2. The calibration plot was established for H2O2 in the concentration range from 50 μM to 1000 μM with 50 μM detection limit, at a signal-to-noise ratio of 3 in a three-electrode cell with a Pt plate as the counter electrode. Additionally, the AgNPs also showed potent antibacterial activity against pathogenic bacteria like E. coli, and S. aureus. © 2017 Elsevier Ltd. All rights reserved.
Biotechnological interventions and genetic diversity assessment in Swertia sp.: a myriad source of valuable secondary metabolites
(Springer Science and Business Media Deutschland GmbH, 2021) Prabhjot Kaur; Devendra Kumar Pandey; R.C. Gupta; Vijay Kumar; Padmanabh Dwivedi; Rupa Sanyal; Abhijit Dey
Abstract: The genus Swertia (Family: Gentianaceae) has cosmopolitan distribution which is present in almost all the continents except South America and Australia. Swertia genus has been renowned as one of the potent herbal drugs in the British, American, and Chinese Pharmacopeias as well as well-documented in the Indian traditional medicinal systems, viz. Ayurveda, Siddha, and Unani. Many species of this genus have therapeutic properties and have been used traditionally in the treatment of a number of health ailments viz. hepatitis, diabetes, inflammation, bacillary dysentery, cancer, malaria, fever etc. This genus is industrially important medicinal plant that has been used as a principal component in numerous marketed herbal/ polyherbal formulations. Medicinal usage of Swertia is endorsed to the miscellaneous compounds viz. xanthones, irridoids, seco-irridoids, and triterpenoids. A chain of systematic isolation of bio-active compounds and their diverse range of pharmacological effects during last 15–20 years proved this genus as industrially important plant. Due to the various practices of the Swertia species, annual demand is more than 100 tons per year for this important herb which is continuously increasing 10% annually. The market value rises 10% by the year as there is increased demand in national and international market resulted in adulteration of many Swertia spp. due to paucity of agricultural practices, exomorphological, phytochemical, and molecular characterization. Thus, efficient biotechnology methods are prerequisite for the mass production of authentic species, sustainable production of bio-active compounds and ex situ conservation. A chain of systematic biotechnological interventions in Swertia herb during last 20 years cover the assessment of genetic diversity, in vitro sustainable production of bio-active compounds and mass propagation of elite genotypes via direct and indirect organogenesis. This review attempts to present the comprehensive assessment on biotechnological process made in Swertia over the past few years. Key points: • Critical and updated assessment on biotechnological aspects of Swertia spp. • In vitro propagation and genetic diversity assessment in Swertia spp. • Biosynthesis and sustainable production of secondary metabolites in Swertia spp. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Biotechnological interventions of in vitro propagation and production of valuable secondary metabolites in Stevia rebaudiana
(Springer Science and Business Media Deutschland GmbH, 2021) Shahnawaz; Devendra Kumar Pandey; Merinashwari Konjengbam; Padmanabh Dwivedi; Prabhjot Kaur; Vijay Kumar; Durga Ray; Puja Ray; Romaan Nazir; Harmeet Kaur; Sidharth Parida; Abhijit Dey
Abstract: Plant cell and tissue culture makes provision of a sustainable and nature-friendly strategy for the production of secondary metabolites, and modern progress in gene editing and genome engineering provides novel possibilities to improve both the qualitative and quantitative aspects of such phytochemicals. The ever-expanding quest for plant-based medicine to treat diabetes facilitates large-scale cultivation of Stevia rebaudiana to enhance the yield of its much-coveted low-calorie sweetener glycosides. The potential to process stevia as a “natural” product should enhance the acceptance of steviosides as a natural calorie-free sweetener especially suitable for use in diabetic and weight control drinks and foods. Besides sweetener agents, S. rebaudiana is a potent source of many antioxidant compounds and is used to cure immunodeficiencies, neurologic disorders, inflammation, diabetes mellitus, Parkinson’s disease, and Alzheimer’s disease. This comprehensive review presents the research outcomes of the many biotechnological interventions implicated to upscale the yield of steviol glycosides and its derivatives in in vitro cell, callus, tissue, and organ cultures with notes on the use of bioreactor and genetic engineering in relation to the production of these valuable compounds in S. rebaudiana. Key points: • Critical and updated assessment on sustainable production of steviol glycosides from Stevia rebaudiana. • In vitro propagation of S. rebaudiana and elicitation of steviol glycosides production. • Genetic fidelity and diversity assessment of S. rebaudiana using molecular markers. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Biotechnological strategies for production of camptothecin from fungal and bacterial endophytes
(Elsevier B.V., 2020) Prabhjot Kaur; Vijay Kumar; Ranjit Singh; Padmanabh Dwivedi; Abhijit Dey; Devendra Kumar Pandey
The horrifying impact of emergence of cancer as an endemic disease worldwide associated with accelerated mortality rate caused significant boost in anticancer drug discovery. The most successful broad spectrum anti-neoplastic monoterpene indole alkaloid camptothecin (CPT) is the product of such natural product based therapeutic approach. This promising anticancer compound, currently approved against cancer, was first isolated from Camptotheca acuminata of Nyssaceae family and was reported as a potent inhibitor of eukaryotic topoisomerase I. Despite its continuous success under clinical studies, low accumulation, slow growth and over-exploitation of Camptotheca acuminata, high extraction cost, complex nature of total, semi and chemical synthesis has failed to meet the industrial demand. As an alternative bio-prospecting route, fermentation of endophytic microbial culture and co-culture of CPT producing plant cell suspension with endophytes have evolved. Endophytes are reported for their contribution in plant growth, disease resistance, stress tolerance and agricultural productivity which may have contributed to scale up the CPT production. This review sums up the current trend in endophytic microbes-based CPT biosynthesis and biotechnological strategies for optimization of CPT yield. Moreover, interaction of endophytic fungi with different host plants under experimental variables, their mode of elicitation, possibility of microbial strain improvement via application of biotechnological strategies and respective lacunas are also being elucidated. © 2020
Biotechnological strategies for the sustainable production of diosgenin from Dioscorea spp.
(Springer Science and Business Media Deutschland GmbH, 2021) Romaan Nazir; Vijay Kumar; Suphala Gupta; Padmanabh Dwivedi; Devendra Kumar Pandey; Abhijit Dey
Abstract: Diosgenin is a plant-derived secondary metabolite mainly present in the members of the plant family Dioscoreaceae. It is a pharmaceutically important compound because of its anti-cancerous, anti-diabetic, anticoagulant, anti-thrombosis, anti-inflammatory, anti-viral, anti-ageing and other properties. Biotechnology provides an opportunity to genetically manipulate cells, tissues, organs or the whole organisms by propagating them in vitro in order to harvest the bioactive compounds. Diosgenin production from botanical sources is being improved by in vitro techniques which include elicitation, genetic transformations and bioconversions. Various techniques have been developed to obtain compounds for drug detection including separation from plants and other natural sources, molecular modelling, synthetic chemistry and combinatorial chemistry. Development in molecular markers determines genetic relationship, genetic linkage map construction, genetic diversity and identification. For rapid clonal propagation and ex situ conservation, the in vitro tools involving plant cell, tissue and organ culture have been well documented for plant-derived diosgenin production. The present review encompasses the wide application of the biotechnological techniques for diosgenin production via elucidating its biosynthetic pathway, in vitro production and mass propagation and elicitation. In addition, molecular marker-mediated diversity assessment of diosgenin containing plant species is also discussed. The review also presents the recent literature to explore the limitations of the relevant studies and future direction of research on production of diosgenin from Dioscorea spp. Key points: • Critical and updated assessment on sustainable production of diosgenin from Dioscorea spp. • In vitro propagation of Dioscorea spp. and elicitation of diosgenin production. • Diversity assessment of Dioscorea spp. using molecular markers. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
Brassinosteroids and their analogs: Feedback in plants under in vitro condition
(Elsevier B.V., 2021) Ankita Singh; Padmanabh Dwivedi; Vijay Kumar; Devendra Kumar Pandey
Brassinosteroids (BRs) are the sixth important plant hormones that induce their effect at micro-level concentration. The importance of its analogous under in vitro condition for many studies includes the study of response in plants aimed at improving various developmental, physiological, morphological, biochemical processes without the involvement of climatic factors, nutrients and diseases. BR improves and increases regeneration and multiplication rate by induction of callus growth, somatic embryos, tracheary elements, shoot elongation, formation of 2embryogenic tissue, stimulation of branch elongation, etc. These provide rapid disease-free clonal propagation of improved varieties within less time and space. BRs improve photosynthetic processes, antioxidant enzymes activities, synthetic seed production and elicitation of secondary metabolites production. Most importantly, it provides resistance from abiotic stresses, for example, oxidative and salinity stress. This review summarizes role of brassinosteroid and its various analogs in improving different morphological, physiological and biochemical attributes in various crop plants grown in vitro, both under normal as well as abiotic stress conditions. © 2021 SAAB
Bright-blue-emission nitrogen and phosphorus-doped carbon quantum dots as a promising nanoprobe for detection of Cr(vi) and ascorbic acid in pure aqueous solution and in living cells
(Royal Society of Chemistry, 2018) Vikas Kumar Singh; Virendra Singh; Pradeep Kumar Yadav; Subhash Chandra; Daraksha Bano; Vijay Kumar; Biplob Koch; Mahe Talat; Syed Hadi Hasan
Highly fluorescent nitrogen and phosphorus-doped carbon quantum dots (N,P-CQDs) were synthesized via a one-step hydrothermal method and fully characterized via various techniques such as TEM, DLS, FT-IR, P-XRD and XPS analysis. The as-synthesized N,P-CQDs showed excellent optical properties and exhibited bright blue colour under UV-light with CIE coordinate (0.20, 0.22) along with a high quantum yield of 73%, due to which they could act as on-off fluorescent nanoprobes for the selective and sensitive detection of highly toxic Cr(vi) below its permissible limit via the inner filter effect (IFE) and static quenching mechanism. In addition, Cr(vi) could be reduced to lower valent chromium species. Therefore, the N,P-CQDs + Cr(vi) system further acted as a selective off-on sensor for reductant ascorbic acid (AA) because it reduced Cr(vi) to Cr(iii) species, resulting in the elimination of IFE and recovery of fluorescence of N,P-CQDs. Notably, this system possesses excellent biocompatibility and negligible cytotoxicity; therefore, it can be potentially applied for fluorescence imaging of intracellular Cr(vi) and ascorbic acid (AA) in living cells and complex biological systems. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Clinical outcomes with all-oral regimens in patients of drug-resistant tuberculosis: A prospective study in a tertiary hospital in North India
(Springer Science and Business Media Deutschland GmbH, 2025) Vijay Kumar; G. S. Sri Bharathi; Mohit Bhatia; Sankha Shubhra Chakrabarti; Upinder Kaur; Jai Krishna Mishra
The study aimed to analyze therapeutic outcomes with bedaquiline-based all-oral regimens for drug-resistant tuberculosis. A prospective observational study was conducted from August 2022 to March 2024 and patients of drug-resistant tuberculosis on all-oral regimens were enrolled. Among 100 patients enrolled (83 on longer-oral and 17 on shorter-oral), 73 patients from longer-oral regimens and 15 from the shorter-oral regimen were followed up at 6 months. Sixty-two (83.8%) patients of longer-oral, and 11 (64.7%) patients of the shorter oral regimen achieved microbiologic improvement in one sample. Clinical improvement occurred in the majority. Forty-five (60.8%) patients in the longer oral and six (35.3%) patients in the shorter-oral regimen required treatment modification, and the major reason was intolerability due to peripheral neuropathy. Skin pigmentation (43.2%), anemia (35.1%), and thrombocytopenia (25.7%) were other common adverse events in longer-oral regimen recipients. Optic neuritis occurred in two patients in the longer-oral regimen. Hepatitis and thrombocytopenia were common with regimens combining bedaquiline and delamanid. Linezolid dose was reduced in 44.6% and was replaced in 17.8% of the patients. Fluoroquinolone resistance emerged in 17.6% and 11.8% of patients in the longer-oral and shorter-oral regimens respectively. Interim microbiological outcomes with all-oral regimens of drug-resistant tuberculosis were favorable. Extended monitoring is needed to assess sustained treatment effect. Adverse events such as peripheral neuropathy are a major challenge and emphasize the need for a reduced dose of linezolid or newer regimens with better safety profiles. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Comparison of efficacy of platelet-rich plasma therapy with or without topical 5% minoxidil in male-type baldness: A randomized, double-blind placebo control trial
(Wolters Kluwer Medknow Publications, 2020) Satyendra Kumar Singh; Vijay Kumar; Tulika Rai
Background: Male-type baldness is a common chronic hair loss disorder among males. Male type baldness is characterized by stepwise miniaturization of the hair follicle, due to alteration in the hair cycle dynamics, leading to transformation of the terminal hair follicle into a vellus one. Platelet-rich plasma (PRP) seems to be a new technique which may improve hair regrowth. We planned a randomized, double-blinded placebo control trial to see the efficacy of PRP with and without topical minoxidil and to compare with placebo and standard treatment. Materials and Methods: The study design was a randomized, double-blind placebo control trial. The sample size was calculated, and randomization was done. Patients with male type baldness were allocated into four groups; first group topical minoxidil only, the second group PRP with minoxidil, the third group normal saline (NS), and fourth group PRP only. Interventions were done monthly for 3 months and patients were followed up for the next 2 months. Effects of interventions were assessed by hair density, patient self-assessment, and clinical photography. Results: A total of 80 patients were included. The maximum improvement was found in PRP with minoxidil group. Increase in hair density (in descending order) was PRP with minoxidil group, PRP-alone group, minoxidil-alone group, while a decrease in hair density was found in NS group, after 5 months. The maximum patient satisfaction was found in PRP with minoxidil group followed by (in descending order), PRP-alone group, minoxidil-alone group, and NS group. Limitation: Long-term follow up of patients was not done. Hair counts and hair thickness estimation were not estimated. Conclusion: In our study, we found PRP with topical minoxidil is more effective than PRP alone and topical minoxidil alone. © 2020 Wolters Kluwer Medknow Publications. All rights reserved.
Comprehensive review of sustainable utilization of Arenga obtusifolia Griff. as a food
(Elsevier B.V., 2024) Saamir Akhtar; Arun Kumar Gupta; Aditi Varshney; Mahek Rawat; Aditya Choudhary; Rohan Kandpal; Avinash Kumar Jha; Sadhna Mishra; Bindu Naik; Vijay Kumar; Rajeev Ranjan; Muzamil Ahmad Rather; Sarvesh Rustagi; Manpreet Singh Preet
This review delves into the utilization of non-conventional starch sources through a specific cultural lens, focusing on the practices and significance of Arenga obtusifolia Griff., commonly referred to as the sugar palm, and its derivative product called Tassey. The tassey is widely popular in the Nyishi tribe of Arunachal Pradesh, India, a region renowned for its biodiversity and abundant palm tree varieties, including the sugar palm. Highlighting the multifaceted dimensions of the sugar palm, this review expounds upon Tassey's creation, consumption, and versatile applications. Tassey, a substance extracted from the sugar palm's stem, emerges as a pivotal element of the Nyishi tribe's cultural heritage and sustenance strategies, especially during times of scarcity and natural calamities. This review sheds light on the integral role played by Nyishi women in the cultivation and preparation of tassey, underscoring their vital contribution to upholding this time-honoured practice. Furthermore, the economic ramifications of tassey production and its commercial viability are explored, elucidating its role in bolstering the tribe's livelihood. Extending beyond its dietary role, tassey exhibits a diverse array of applications, spanning from human consumption to its incorporation in the crafting of traditional alcoholic beverages and even as a therapeutic resource for livestock. By offering insights into the profound relationship between the Nyishi tribe and the sugar palm, this review enriches our comprehension of traditional ecological wisdom and sustainable exploitation of resources within a culturally vibrant backdrop. Ultimately, this comprehensive exploration contributes to a nuanced appreciation of the intricate interplay between heritage, environment, and innovation in this distinctive region. © 2023 The Author(s)
Conductance and conduction noise of polycrystalline La0.7Ca0.2Ba0.1MnO3 films on different substrates
(2006) D.P. Singh; Vijay Kumar; G.L. Bhalla; P.K. Siwach; O.N. Srivastava; Neeraj Khare
La0.7Ca0.2Ba0.1MnO3 (LCBMO) films were prepared by ultrasonically assisted spray pyrolysis deposition on LaAlO3 and Al2O3 single crystal substrates. Conductance-voltage (G-V) characteristics and conduction noise of the two films were found to be different. G-V characteristics of LCBMO film on LaAlO3 were linear indicating the spin dependent scattering across the grain boundaries whereas for the film on Al2O3, G-V characteristics at low temperature (T < 210 K) were nonlinear indicating dominant transport mechanism as spin polarized tunnelling. Normalized conduction noise of LCBMO film on LaAlO3 was one order lower to that of film on Al2O3. These differences in conductance-voltage and conduction noise characteristics of the two films are attributed to the presence of more disordered grain boundaries in LCBMO film on Al2O3 as compared to the films on LaAlO3 substrate. © 2006 Elsevier Ltd. All rights reserved.
Corrigendum to “Screening of elite germplasms for industrially valuable medicinal crop Stevia rebaudiana for stevioside and rebaudioside A production: An HPTLC-linked chemotaxonomic assessment” (South African Journal of Botany (2022) 150 (1159–1167), (S0254629922004823), (10.1016/j.sajb.2022.09.004))
(Elsevier B.V., 2023) Shah Nawaz; Prabhjot Kaur; Merinaswari Konjengbam; Vijay Kumar; R.C. Gupta; Padmanabh Dwivedi; Babita Patni; Babita Pandey; Abhijit Dey; Devendra Kumar Pandey
The authors regret that the incorrect Fig. 3 was published in the original article. The correct Fig. 3 is provided herein and this will not affect the results and conclusion of the manuscript. The authors would like to apologise for any inconvenience caused. © 2023 South African Association of Botanists
Defence structure development in Rhizopus nigricans during mycoparasitism by Fusarium oxysporum F. sp. lycopersici
(Martinus Nijhoff/Dr. W. Junk Publishers, 1981) S.P. Pathak; Vijay Kumar; R.S. Dwivedi
The colony interaction and hyphal interference between F. oxysporum f. sp. lycopersici and R. nigricans were studied. Intermingling growth of both colonies was observed. Hyphal parasitism was characterized by coiling, penetration, ramification inside host, rupture of host hyphae and frequent chlamydospore formation. The host hyphae bulged out and deposited a 'wall like barrier'. The parasite penetrated the barrier and developed further. © 1981 Martinus Nijhoff/Dr. W. Junk Publishers.
Development and Characterization of Zn(98−x).Mg2.(SiC)x Composites Synthesized in Graphite Packed Non-oxidizing Media
(Springer, 2021) Amrendra Rai; Pooja Rai; Vijay Kumar; Naresh Kumar Singh; Vinay Kumar Singh
Zinc-based composites have diverse areas of applications; in this context, Zn-Mg-based composite Zn(98−x).Mg2.(SiC)x (x = 0, 2, 4, 6 and 8 wt.%) was synthesized by sintering in non-oxidizing graphite packed media, which can be used as a degradable orthopedic implant. The assessment of mechanical properties, corrosion behavior and localized discharge of zinc ions in simulated body fluid after a certain interval of time was done. The results acquired from various investigations reveal that the composite with Zn92.Mg2.(SiC)6 has a maximum compressive strength of 106 MPa, flexural strength 92 MPa, hardness 55.48 VHN and Young’s modulus 50.353 GPa. The strengthening of the composites was enhanced because of the strain hardening effect of the reinforced SiC particles, which hinders the movement of the dislocations. Surface characteristics and phases evolved in the composite were analyzed by SEM and XRD Technique. © 2021, ASM International.
Effect of alkoxy chain density on the mesogenic properties of aroylhydrazone based liquid crystals: synthesis, characterisation, photophysical and gelation behaviour
(Taylor and Francis Ltd., 2020) Priyanka Kanth; Hemant Kumar Singh; Vijay Kumar; Sachin Kumar Singh; D. S. Shankar Rao; S. Krishna Prasad; Bachcha Singh
Three series of ester linkage containing aroylhydrazone based compounds have been synthesised where density and length of alkoxy chains are varied sequentially at ester end, keeping amide end of the molecule the same to investigate the effect of alkoxy chain density. The series of the compounds with single alkoxy chain at 4- position at ester terminal show nematic mesophase. The series with two alkoxy chains at 3- and 5- positions exhibit columnar rectangular mesophase and the series with three alkoxy chains at 3-, 4- and 5- positions show columnar oblique mesophase. It was observed that increasing the number of alkoxy chains at ester terminal, self-assembly of molecules changes and leads to a change from nematic to columnar mesophase and also significant enhancement in the mesomorphic range. Temperature dependent Raman studies confirm the presence of intermolecular hydrogen bonding which assist the self-assembly and gelation properties of molecules. All the series show similar photophysical properties despite the fact that the series vary in their molecular structures. Representative compounds of each series exhibited gelation in hydrocarbon solvents. FESEM images of the gels showed interwoven network of nanofibers of several micrometres length. These supergelators may be good candidates for applications in electronic devices. © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Effect of regioisomerism on the self-assembly, photophysical and gelation behavior of aroylhydrazone based polycatenars: Synthesis and characterization
(Elsevier B.V., 2019) Priyanka Kanth; Hemant Kumar Singh; Vijay Kumar; Sachin Kumar Singh; D.S. Shankar Rao; S. Krishna Prasad; Bachcha Singh
In this paper we report five series of aroylhydrazone based polycatenars differing from each other in number and position of alkoxy chains on one end of the core; keeping other end the same. A systematic variation in the structures was carried out to understand the effect of position and chain length on the mesophase behavior. In the case of single alkoxy chain at 4-position, there is a transition from Smectic C to Smectic A mesophase during cooling and Smectic A to Smectic C transition in heating cycle in all the homologues except n = 6 & n = 8. In the case of two alkoxy chains at 3-, 5-positions, the compounds are non-mesogenic in nature. On changing the position of alkoxy chains from 3-, 5-positions to 3-, 4-positions, intermolecular forces weaken and these compounds become liquid crystalline and show columnar rectangular mesophase resulting from the effect of regioisomerism. Moving on to the series with three alkoxy chains, it was observed that 2-, 3-, 4-trialkoxy substituted compounds exhibit columnar rectangular mesophase except lower chain length (n = 6 & 8) while 3-, 4-, 5-trialkoxy substituted aroylhydrazones show columnar rectangular mesophase; except n = 10 which shows columnar oblique mesophase. Thus it was established that on increasing density of alkoxy chains around one terminal, mesophase changes from smectic to columnar mesophase. Temperature dependent Raman studies confirm the presence of intermolecular hydrogen bonding. Further, effect of substitution pattern did not show much influence on the photophysical properties of the mesogenic series in solid and solution state. However, the non-mesogenic series showed a different absorption and emission transition from the mesogenic series in solid and solution state. Solid state fluorescence studies show almost similar emission maxima in all the series. However, it was also noticed that non-mesogenic series show maximum red shifted emission maxima in solid state as compared to that of solution. All the series showed good gelation properties with less than 1% CGC (wt%) suggesting the strong ability of molecules to form gel. These H-bonded liquid-crystalline gels have immense potential for applications in emissive displays. © 2019 Elsevier B.V.
Effect of Sintering Temperature on the Physico-Mechanical Behavior of SiC Reinforced Zinc-Magnesium Based Composite
(Korean Institute of Metals and Materials, 2021) Amrendra Rai; Pooja Rai; Vijay Kumar; Naresh Kumar Singh; Vinay Kumar Singh
Abstract: The present research work deals with study the effect of sintering temperature on the physical and mechanical behavior of Zn2Mg6SiC composite, which can be used as a biodegradable implant. Sintering of the composite has been done at a temperature of 430 °C, 450 °C, 470 °C and 490 °C. The mechanical and physical properties of the samples have been observed to vary with sintering temperature. The grain size of the samples has observed to be optimized at 450 °C with grain size 0.2587 µm and provides maximum strength to the samples. The densification of the composites achieved was found to be maximum at 450 °C having a value 90.30%. Wear rate, hardness, Young’s Modulus of elasticity and flexural strength were observed to be maximum at this temperature. Scanning electron microscopy and X-ray diffraction spectroscopy of the samples at various temperatures were done to find microstructural changes and surface morphology of the composite. Graphic Abstract: [Figure not available: see fulltext.]. © 2020, The Korean Institute of Metals and Materials.
Effect of untreated bed nets on blood-fed Phlebotomus argentipes in kala-azar endemic foci in Nepal and India
(Fundacao Oswaldo Cruz, 2009) Albert Picado; Vijay Kumar; Murari Das; Ian Burniston; Lalita Roy; Rijal Suman; Diwakar Dinesh; Marc Coosemans; Shyam Sundar; Kesari Shreekant; Marleen Boelaert; Clive Davies; Mary Cameron
Observational studies in the Indian subcontinent have shown that untreated nets may be protective against visceral leishmaniasis (VL). In this study, we evaluated the effect of untreated nets on the blood feeding rates of Phlebotomus argentipes as well as the human blood index (HBI) in VL endemic villages in India and Nepal. The study had a "before and after intervention" design in 58 households in six clusters. The use of untreated nets reduced the blood feeding rate by 85% (95% CI 76.5-91.1%) and the HBI by 42.2% (95% CI 11.1-62.5%). These results provide circumstantial evidence that untreated nets may provide some degree of personal protection against sand fly bites.