Browsing by Author "Dheeraj Kumar Singh"

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Modeling the weak hydrogen bonding of pyrrole and dichloromethane through Raman and DFT study
(2012) Dheeraj Kumar Singh; Birendra Pratap Asthana; Sunil Kumar Srivastava
Raman spectra of neat pyrrole (C4H5N) and its binary mixtures with dichloromethane (CH2Cl2, DCM) with varying mole fractions of C4H5N from 0.1 to 0.9 were recorded in order to monitor the influence of molecular interaction on spectral features of selected vibrational bands of pyrrole in the region 600-1600 cm-1. Only 1369 cm-1 vibrational band of pyrrole shows a significant change in its peak position in going from neat pyrrole to the complexes. The 1369 cm-1 band shows (∼6 cm-1) blue shift upon dilution and the corresponding linewidth shows the maximum shift at C=0.5 mole fraction of pyrrole upon dilution which clearly indicates that the concentration fluctuation model plays major role. Quantum chemical calculation using density functional theory (DFT) and ab-initio (MP2 and HF) methods were performed employing high level basis set, 6-311++G(d,p) to obtain the ground state geometry of neat pyrrole and its complexes with DCM in gas phase. Basis set superimpose error (BSSE) correction was also introduced by using the counterpoise method. In order to account for the solvent effect on vibrational features and changes in optimized structural parameters of pyrrole, polarizable continuum model (PCM) (bulk solvations) and PCM (specific plus bulk solvations) calculations were performed. Two possible configurations of pyrrole + DCM complex have been predicted by B3LYP and HF methods, whereas the MP2 method gave only single configuration in which H atom of DCM is bonded to π ring of the pyrrole molecule. This affects significantly the ring vibrations of pyrrole molecule, which was also observed in our experimental results. © Springer-Verlag 2012.
Mycosynthesis of bactericidal silver and polymorphic gold nanoparticles: Physicochemical variation effects and mechanism
(Future Medicine Ltd., 2018) Dheeraj Kumar Singh; Jitendra Kumar; Vijay Kumar Sharma; Satish Kumar Verma; Arti Singh; Puja Kumari; Ravindra Nath Kharwar
Aim: Extracellular synthesis of silver and gold nanoparticles using aqueous cell-free filtrate (CFF) of endophytic Chaetomium globosum and characterization of its bioactive proteins. Methods: Temperature and pH gradients were used to assess their effects on dimensions of NPs. NPs were tested in vivo for antibacterial activity. MALDI-TOF-MS/MS was used for characterization of CFF proteins. Results: Fungal CFF fabricated nanoparticles of various shape under varied physicochemical conditions. Silver nanoparticles showed significantly (p ≤ 0.5) enhanced antibacterial activity against Staphylococcus aureus and Klebsiella pneumoniae compared with AgNO3. Two prominent CFF proteins showed homology with benzoate 4-monooxygenase cytochrome P450 and ubiquinol-cytochrome c reductase. Conclusion: The study achieved controlled mycosynthesis of NPs and explains the hitherto poorly known mechanism of reduction, stabilization and antibacterial activity of nanoparticles. © 2018 Future Medicine Ltd.
Phytochemical analysis and antimicrobial activity of an endophytic Fusarium proliferatum (ACQR8), isolated from a folk medicinal plant Cissus quadrangularis L.
(Elsevier B.V., 2021) Arti Singh; Jitendra Kumar; Vijay Kumar Sharma; Dheeraj Kumar Singh; Puja Kumari; Jay Hind Nishad; Veer Singh Gautam; Ravindra Nath Kharwar
The endophytic fungi are an important source of bioactive natural products. This study includes evaluation of antimicrobial activity and phytochemical analysis of endophytic fungus ACQR8, recovered from the root tissues of a folk medicinal plant Cissus quadrangularis L., which was identified as Fusarium proliferatum by microscopic and molecular methods. The fungus showed broad spectrum antibacterial and antifungal activities against variety of important plant and human pathogens. To the best of our knowledge, this is the first study to record antifungal activity of any endophytic Fusarium sp. against phytopathogens Rhizoctonia solani, Fusarium oxysporum and the dermatophytes Trichophyton mentagrophyte and Microsporum gypseum. The minimum inhibitory concentration of the crude extract ranged from 40–120 µg/ml against pathogenic bacteria and 0.2–2.5 mg/ml against fungal pathogens. Besides, this study probably is also the first to document the phytochemical constituents of an endophytic Fusarium sp. Phytochemical testing and GC-MS (gas chromatography- mass spectrometry) analysis revealed the presence of fatty acids and its derivatives, phenolics, terpenoids and unsaturated alkenes in the crude extract which scientifically validates the highly promising antibacterial and antifungal activity exhibited by endophytic isolate ACQR8. © 2021 SAAB