Akella Sivaramakrishna

A short review on stable metal nanoparticles using ionic liquids, supported ionic liquids, and poly(ionic liquids)

Metal nanoparticles (NPs) are a subject of global interest in research community due to their diverse applications in various fields of science. The stabilization of these metal NPs is of great concern in order to avoid their agglomerization during their applications. There is a huge pool of cations and anions available for the selection of ionic liquids (ILs) as stabilizers for the synthesis of metal NPs. ILs are known for their tunable nature allowing the fine tuning of NPs size and solubility by varying the substitutions on the heteroatom as well as the counter anions. However, there has been a debate over the stability of metal NPs stabilized by ILs over a long period of time and also upon their recycling and reuse in organocatalytic reactions. ILs covalently attached to solid supports (SILLPs) have given a new dimension for the stabilization of metal NPs as well as their separation, recovery, and reuse in organocatalytic reactions. Poly(ILs) (PILs) or polyelectrolytes have created a significant revolution in the polymer science owing to their characteristic properties of polymers as well as ILs. This dual behavior of PILs has facilitated the stabilization of PIL-stabilized metal NPs over a long period of time with negligible or no change in particle size, stability, and size distribution upon recycling in catalysis. This review provides an insight into the different types of imidazolium-based ILs, supported ILs, and PILs used so far for the stabilization of metal NPs and their applications as a function of their cations and counter anions.

Biophysical Characterization and Molecular Docking Studies of Imidazolium Based Polyelectrolytes−DNA Complexes: Role of Hydrophobicity

Nonviral gene delivery vectors are acquiring greater attention in the field of gene therapy by replacing the biological viral vectors. DNA-cationic polymer complexes are one of the most promising systems to find application in gene therapy. Hence, a complete insight of their biophysical characterization and binding energy profile is important in understanding the mechanism involved in nonviral gene therapy. In this investigation, the interaction between calf thymus DNA (ctDNA) and imidazolium-based poly(ionic liquids) (PILs) also known as polyelectrolytes with three different alkyl side chains (ethyl, butyl, and hexyl) in physiological conditions using various spectroscopic experiments with constant DNA concentration and varying polyelectrolyte concentrations is reported. UV-visible absorption, fluorescence quenching studies, gel electrophoresis, circular dichroism (CD), and Fourier transform infrared spectroscopy (FTIR) have confirmed the binding of polyelectrolytes with DNA. UV-vis absorption measurements and fluorescence quenching revealed that the binding between DNA and the polyelectrolyte is dominated by electrostatic interactions. Additionally, CD and FTIR results indicated that the DNA retained its B-form with minor perturbation in the phosphate backbone without significant change in the conformation of its base pairs. Preference for alkyl side chains (K(PIL-Ethyl Br) < K(PIL-Butyl Br) < K(PIL-Hexyl Br)) toward efficient binding between the polyelectrolyte and DNA was inferred from the binding and quenching constants calculated from the absorption and emission spectra, respectively. Further, in silico molecular docking studies not only validated the observed binding trend but also provided insight into the binding mode of the polyelectrolyte-DNA complex.

Assessment on the antibacterial activity of nanosized silica derived from hypercoordinated silicon(IV) precursors

Silica nanoparticles were synthesized through a versatile sol–gel combustion method from hydrazide based hypercoordinated silicon complexes derived from the reaction of silicon tetrachloride with O-silylated hydrazide derivatives. The complexes were characterized by 1H, 13C, 29Si NMR and ESI-mass spectrometric techniques. A refined morphology was observed in the product after sintering i.e. from spherical to rod shaped nanoparticles. The powder X-ray diffraction patterns and the TEM images of silica show the formation of silica nanoparticles. The IR spectra show Si–O linkages and DLS studies indicate the particle size distribution to be between 20 and 100 nm for the material before sintering and 70–120 nm after sintering at 1000 °C. A TEM image of the decomposed gel indicates the formation of crystalline silica rods. This work also demonstrates the influence of nano-sized silica particles on antibacterial activity (DIZ, MIC and MBC) i.e. better activity was shown for nano-rods derived from the hypercoordinated silicon complexes than the conventional TEOS (sol–gel) method. Experiments on the generation of reactive oxygen species (ROS) through oxidative stress demonstrate the toxicity of nanosilica particles.

Spectroscopic and In Silico Evaluation of Interaction of DNA with Six Anthraquinone Derivatives

Anthraquinones consist of several hundreds of derivatives that differ in the nature and positions of substituent groups which are known to have several biological activities including antitumor properties. Interaction of molecules with DNA persists to be an extremely vital parameter while endeavouring to formulate therapeutics. In this study, few anthraquinone derivatives such as 1,2-dihydroxyanthraquinone (alizarin), 1,4-dihydroxyanthraquinone (quinizarin), 1,8-dihydroxyanthraquinone (danthron), 1,2,4-trihydroxyanthraquinone (purpurin), 1,4-diaminoanthraquinone, and 1-methylaminoanthraquinone were analyzed for its possible interaction with calf-thymus DNA through spectroscopy and in silico analysis. Our UV spectroscopic results indicate that all selected anthraquinones interact with DNA probably by external binding. Molar extinction coefficient has been calculated for chosen six anthraquinones. FT-IR results suggest that significant shifts of peaks as well as disappearance of certain characteristic peaks were indicators of the plausible interaction going on due to dye-DNA adduct formation. Among the six dyes used, purpurin showed better results and indicates the relatively strong binding affinity with DNA. Our molecular modeling results also show that purpurin has comparatively higher DNA interaction with a score of −6.18 compared with the ethidium bromide of −5.02 and intercalate the DNA.

Ni Nanoparticles Stabilized by Poly(Ionic Liquids) as Chemoselective and Magnetically Recoverable Catalysts for Transfer Hydrogenation Reactions of Carbonyl Compounds

Imidazolium‐based poly(ionic liquids) with hydroxide as the counter anion were employed to prepare stable aqueous dispersion of Ni nanoparticles. The synthesized poly(ionic liquid) stabilized Ni nanoparticles (PIL‐Ni‐NPs) were characterized by thermogravimetric analysis (TGA), vibrating sample magnetometry (VSM), powder XRD, TEM, Brunauer–Emmett–Teller (BET) surface area measurements, X‐ray photoelectron spectroscopy (XPS), EPR, and UV/Vis spectroscopy. The PIL‐Ni‐NPs possess good catalytic activity towards transfer hydrogenation (TH) reactions of carbonyl compounds to their alcohol derivatives, in isopropanol at 80 °C in the absence of any additional base. This catalyst system chemoselectively reduces only the carbonyl group of α,β unsaturated carbonyl compounds. The magnetically separable PIL‐Ni‐NPs were recycled and reused for further TH reactions.

Review: active homogeneous reagents and catalysts in n-alkane activation

The development of selective, efficient, and direct routes for activation and functionalization of naturally abundant n-alkanes could lead to a new paradigm in materials and energy technologies. In this context, the use of homogeneous catalysts to functionalize C–H bonds of unactivated hydrocarbons is of particular interest from a scientific as well as an economic viewpoint. Despite the large body of work on stoichiometric C–H activation reactions produced over the last three decades, relatively few systems have been developed to allow catalytic functionalization of hydrocarbons. This review deals with homogeneous catalytic processes available in the literature for paraffin activation and functionalization. The key intermediates involved in catalytic systems are highlighted, providing important information in the design of new and efficient catalysts. Also, some of the key challenges and approaches to rational development of the next generation of organometallic catalysts will be highlighted.

Studies on interaction of norbixin with DNA: Multispectroscopic and in silico analysis

The interaction of food colorant norbixin with calf thymus DNA (CTDNA) was investigated through UV-Visible spectroscopy, Fourier Transform Infrared (FTIR), Circular Dichroism (CD), Nuclear Magnetic Resonance (NMR), DNA melting studies, electrophoretic analysis, histological staining technique and molecular docking studies. The results indicated that norbixin interacted with CTDNA by partial intercalation mode. The binding constant (K) of norbixin with CTDNA was calculated to be 5.08×10(5) Mol(-1) L. FTIR and CD studies were coupled with (1)H NMR spectra revealed that norbixin intercalates partially and binds to the grooves, phosphate group, deoxyribose sugar of DNA and also induces conformational transition of B-form to A-form DNA. Agarose gel electrophoretic and histological staining technique results further prove that, norbixin specifically binds to the DNA in the cell. Moreover, molecular docking studies on the specific binding of norbixin with CTDNA have exhibited lowest conformation energy score of -3.2. Therefore, this food colorant has the ability to interact with DNA and it could emerge as a promising class of natural DNA targeted therapeutic.

Experimental and theoretical studies on extraction behavior of di-n-alkyl phosphine oxides towards actinides

Di-n-alkyl phosphine oxides (DAPOs) with different alkyl chain length viz. C6, C7, C8 and C10 and their corresponding Th(IV) and La(III) complexes were synthesized and characterized using FT-IR, 1H, 31P{1H}, and 13C NMR. The extraction behavior of U(VI) and Am(III) with DAPOs was investigated and it largely depends on nitric acid concentration. These DAPOs showed the highest distribution coefficients with U(VI) among U(VI) and Am(III). The DU(VI) values of DAPOs are higher at lower acidities i.e. 0.1 M nitric acid concentration. Among the four tested DAPOs for the extraction of uranium with a molar concentration of 0.025 M, DDPO bearing the longest alkyl chains showed the highest DU(VI) values of 84.6 and their distribution coefficients increased with an increase in alkyl chain length in the tested DAPOs. Here we have proposed a mechanism for the extraction of actinides using di-n-alkyl phosphine oxides, which was further supported by theoretical calculations. At lower acidity, DAPO behaves like an acidic extractant and extracts the metal ion via a cation exchange mechanism. On the contrary, at higher acidity, the metal ions are extracted via a solvation mechanism through phosphoryl group coordination. Density functional theory (DFT) calculations support a bimolecular mechanism for the tautomerism reaction in the DHePO (di-n-hexyl phosphine oxide) ligand, where both pentavalent (tetracoordinate) and trivalent phosphorus are in equilibrium. An activation barrier of ∼27.3 kcal mol−1 is estimated with respect to the reactant complex at the B3LYP/def2-TZVP level. The length of the alkyl chain in di-n-alkyl phosphine oxides (DAPO) also plays a significant role in actinide extraction at lower acidity.

Bioremediation of p-Nitrophenol by Pseudomonas putida 1274 strain

Backgroundp-Nitrophenol (PNP) occurs as contaminants of industrial effluents and it is the most important environmental pollutant and causes significant health and environmental risks, because it is toxic to many living organisms. Nevertheless, the information regarding PNP degradation pathways and their enzymes remain limited.ObjectiveTo evaluate the efficacy of the Pseudomonas Putida 1274 for removal of PNP.MethodsP. putida MTCC 1274 was obtained from MTCC Chandigarh, India and cultured in the minimal medium in the presence of PNP. PNP degradation efficiency was compared under different pH and temperature ranges. The degraded product was isolated and analyzed with different chromatographic and spectroscopic techniques.ResultsP. putida 1274 shows good growth and PNP degradation at 37°C in neutral pH. Acidic and alkali pH retarded the growth of P. putida as well as the PNP degradation. On the basis of specialized techniques, hydroquinone was identified as major degraded product. The pathway was identified for the biodegradation of PNP. It involved initial removal of the nitrate group and formation of hydroquinone as one of the intermediates.ConclusionOur results suggested that P. putida 1274 strain would be a suitable aspirant for bioremediation of nitro-aromatic compounds contaminated sites in the environment.

Investigations on synthesis, thermolysis, and coordination chemistry of aminophosphine oxides

Some aminophosphine oxides (AmPOs), (R 1)(R 2)(R 3)P=O [R 1 = R 2 = R 3 = HNCH2CH=CH2; R 1 = R 2 = Ph, R 3 = HNCH2CH=CH2; R 1 = R 2 = R 3 = HNNMe2; R 1 = R 2 = Ph, R 3 = HNNMe2; R 1 = R 2 = R 3 = NC4H8O; R 1 = R 2=Ph, R 3 = NC4H8O], have been synthesized. The coordination chemistry of these AmPOs is studied with La(III), Th(IV), and U(VI) salts. The products are characterized by various analytical and spectroscopic techniques, and the thermal properties of the ligands and their complexes examined. The TGA data for these compounds show different decomposition temperatures, as well as thermal stability of the metal complexes. Comparisons are made among different ligands on their selective complexing ability towards some chosen metal salts. Mulliken population analysis shows that the basicity of P=O of ligand increases with an increase in the number of P-bonded amino groups.