Browsing by Author "Singh, R."

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Cyclocondensation reactions of an electron deactivated 2-aminophenyl tethered imidazole with mono/1, 2-biselectrophiles: synthesis and DFT studies on the rationalisation of imidazo [1, 2-a] quinoxaline versus benzo [f] imidazo [1, 5-a][1, 3, 5] triazepine selectivity switches.
(Royal Society of Chemistry, 2018) Joshi, G.; Chauhan, M; Kumar, R; Thakur, A; Sharma, S; Singh, R.; Wani, A.A.; Sharon, A.; Bharatam, P.V; Kumar, R.
Microwave-promoted ring-closure reactions of 5-amino-1-(2-aminophenyl)-1H-imidazole-4-carbonitrile (7) with various mono/1,2-biselectrophiles are presented. The reaction of 7 with aldehydes, ketones and isocyanates produced the corresponding Pictet–Spengler (PS) products i.e. the imidazo[1,2-a]quinoxaline ring system via 6-endo-trig cyclisation. On the other hand, the reaction of 7 with CH(OEt)3, and CDI resulted in the formation of benzo[f]imidazo[1,5-a][1,3,5]triazepine scaffolds via a 7-exo-trig cyclisation process. The mechanistic aspects of these ring cyclisation processes have been analysed and studied to rationalise 6- versus 7-membered ring formation using density functional theory (DFT). DFT calculations revealed the involvement of N-Heterocyclic Carbene (NHC) in the PS reaction mechanism.
Evaluation of genetic fidelity of in vitro raised plants of Dendrocalamus asper (Schult. & Schult. F.) Backer ex K. Heyne using DNA-based markers
(2013) Singh, S.R.; Dalal, S.; Singh, R.; Dhawan, A.K.; Kalia, R.K.
Dendrocalamus asper, an edible bamboo is valued for its tender edible shoots in the food industry. However, overexploitation of natural stands of D. asper coupled with minimal conservation and reforestation efforts has led to its rapid depletion in nature. Therefore protocol for rapid multiplication of D. asper via direct regeneration using nodal segments from mature clumps was standardized and more than 25,000 plants were transferred to the field (Singh et al. 2012a). However, genetic fidelity of these in vitro raised plants needs to be authenticated for commercial scale application of the developed micropropagation protocol. PCR-based molecular markers have emerged as simple, fast, reliable and labor-effective tools for testing the genetic fidelity of in vitro raised plants. This study report the genetic fidelity analysis of in vitro raised plants of D. asper for the first time using arbitrary (Random Amplified Polymorphic DNA, RAPD), semi-arbitrary (Inter-Simple Sequence Repeat, ISSR; Amplified Fragment Length Polymorphism, AFLP), and sequence-based (Simple Sequence Repeat, SSR) markers. Bulked DNA samples of 20 in vitro raised shoots (collected after every three subculture cycles starting from 3rd to 30th passage) and field transferred plantlets were compared with the mother plant DNA using 90 primer combinations (25 each of RAPD, ISSR, SSR, and 15 AFLP) and scorable bands were produced by 78 (22 RAPD, 24 ISSR, 21 SSR, and 11 AFLP) primers. A total of 146 distinct and scorable bands were produced by 22 RAPD primers with an average of 6. 6 bands per primer while the number of bands for ISSR primers varied from 3 (ISSR-4 and 9) to 13 (ISSR-17), with an average of 7. 1 bands per primer. Similarly, SSR markers also showed wide variation in number of bands, ranging from 2 (RM 261) to 12 (RM 44, 140, and 224) with an average of 7. 8 bands. AFLP primer combinations could generate 35-72 bands with an average of 48. 7 bands per primer pair. Amplification of monomorphic bands with all primer combinations authenticated the true to type nature of the in vitro raised plants of D. asper which underwent up to 30 subculture passages over a period of approximately 2 years thereby supporting the commercial utilization of the developed micropropagation protocol. ? 2012 Franciszek G?rski Institute of Plant Physiology, Polish Academy of Sciences, Krak
Impact of rice-husk ash on the soil biophysical and agronomic parameters of wheat crop under a dry tropical ecosystem
(Elsevier B.V., 2018) Singh, R.; Srivastava, P.; Singh, P.; Sharma, A.K.; Singh, H.; Raghubanshi, A.S.
Several alternative amendments like organic manure and biochar have been proposed for revitalizing the degrading soil viability and fertility for sustainable agriculture, globally. However, detailed field-scale studies focussing on the soil and agronomic parameters of crops under these amendments are limited in dry tropical ecosystems. Therefore, we studied the impact of various soil amendments viz., rice-husk ash (RHA) and farm-yard manure (FYM) along with mineral fertilizer on soil biophysical and agronomic parameters of wheat crop. We specifically explored the impact of the amendments on soil CO2 efflux (SCE, under different growth stages) and the harvest index of wheat crop, which are considered as the key indicators of soil viability and agronomic efficiency, respectively. SCE, soil moisture, soil temperature, soil N, microbial biomass and soil pH were found significantly varying under different treatments (P < 0.05). SCE was found maximum under sole FYM applied and minimum under mineral fertilizer applied treatments, whereas RHA application lowered the SCE as compared to sole FYM application. Moreover, SCE showed variation with plant growth stages, and found maximum during stem elongation followed by heading stage whereas minimum during ripening stage. Soil moisture was found to have considerable regulation for the overall variation in SCE (r2 = 0.17; P = 0.04). In contrast to the soil properties, agronomic parameters (except harvest index) were found higher under mineral fertilizer applied treatments followed by sole FYM and combined FYM + RHA treatments, whereas sole RHA applied treatment showed minimum values. However, significant variations were observed only for harvest index, aboveground dry matter, grain and straw yields (P < 0.05). Further, harvest index was found highest under sole and combined FYM and RHA applied treatments whereas lowest in mineral fertilizer applied treatments. Soil C/N ratio (r2 = 0.16; P = 0.04) and panicle length (r2 = 0.18; P = 0.03), respectively as soil and agronomic parameters, have been found to have considerable control over harvest index. The findings revealed that soil viability is higher under sole FYM and combined FYM + RHA treatments whereas mineral fertilization enhances agronomic performance. Based on the studied two indicators, we conclude that both soil and agronomic sustainability can be maintained by using a combination of organic (FYM and RHA) fertilization with reduced inputs from mineral fertilizers. However, it further needs exploration for various soil and plant eco-physiological parameters of different crops at field level for wider adaptation in the dry tropical region. ? 2018 Elsevier Ltd