Rakesh Kumar

Hallmarks of mechanochemistry: from nanoparticles to technology

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

Recycled chitosan nanofibril as an effective Cu(II), Pb(II) and Cd(II) ionic chelating agent: Adsorption and desorption performance

Mechanically disassembled chitosan nanofibrils were prepared and used as metal ion chelating agents. Structure and morphology of nanofibrils were investigated and ionic adsorption or desorption performance were validated to establish related fitting models. In single metal ion solution, the saturated adsorption capacities of Cu(II), Pb(II), Cd(II), Zn(II), and Ni(II) were 168.66, 118.00 and 60.85, 143.67, and 63.32 mg/g, respectively. In ternary metal ion solution, Cu(II) was more competitive to be adsorbed than Pb(II) and Cd(II) and its removal could arrive at 60%. Ions adsorbed by nanofibrils could be released by EDTA and the recovery could keep above 70% after 3 sorption-desorption cycles. Hence, renewable and recyclable nanofibrillar chitosan exhibited a great promising application in metal treatments attributed to its high adsorption capacity and chelation efficiency.

Chlorpyrifos induces apoptosis and DNA damage in Drosophila through generation of reactive oxygen species

The present study investigated the apoptosis and DNA damage inducing potential of chlorpyrifos (CP) in Drosophila melanogaster. Third instar larvae of Drosophila were treated with different concentrations of CP (0.015-15.0 microg/L) for 2-48 h. Reactive oxygen species (ROS) generation, oxidative stress markers, DNA damage and apoptotic cell death end points were measured in them. A significant increase in DNA damage was concomitant with apoptotic mode of cell death in 15.0 microg/L CP-treated organisms for 24 and 48 h. Depolarization in mitochondrial membrane potential and increased casapase-3 and caspase-9 activities in these organisms indicated both as potential targets of CP. A significant positive correlation was observed among ROS generation, apoptosis and DNA damage. The study suggests that (i) ROS may be involved in inducing apoptosis and DNA damage in the CP-exposed larvae of Drosophila and (ii) D. melanogaster may be used as an alternative in vivo animal model for xenobiotics hazard assessment.

Biocompatibility of polymethylmethacrylate resins used in dentistry

Biocompatibility or tissue compatibility describes the ability of a material to perform with an appropriate host response when applied as intended. Poly-methylmethacrylate (PMMA) based resins are most widely used resins in dentistry, especially in fabrication of dentures and orthodontic appliances. They are considered cytotoxic on account of leaching of various potential toxic substances, most common being residual monomer. Various in vitro and in vivo experiments and cell based studies conducted on acrylic based resins or their leached components have shown them to have cytotoxic effects. They can cause mucosal irritation and tissue sensitization. These studies are not only important to evaluate the long term clinical effect of these materials, but also help in further development of alternate resins. This article reviews information from scientific full articles, reviews, or abstracts published in dental literature, associated with biocompatibility of PMMA resins and it is leached out components. Published materials were searched in dental literature using general and specialist databases, like the PubMED database.

Palladium‐Catalyzed Dehydrative Heck Olefination of Secondary Aryl Alcohols in Ionic Liquids: Towards a Waste‐Free Strategy for Tandem Synthesis of Stilbenoids

All in one: a tandem strategy has been developed wherein secondary aryl alcohols are directly coupled with aryl halides to provide stilbenoids through a dehydrative Heck sequence in the ionic liquid [hmim]Br, and with water as a by-product under microwave irradiation. Classical methods do not permit this sequence to proceed in one pot, and some methods require multiple steps. hmim=1-n-hexyl-3-methylimidazolium.

Stirred Bead Mill Grinding of Gibbsite: Surface and Morphological Changes

This paper describes the structural and surface changes in gibbsite subjected to mechanical activation using stirred media mill. During milling, the median particle size decreased from 124 to around 3 μm in 30 min indicating high milling efficiency. Scanning electron microscopy studies revealed that gibbsite particles, present in the feed as agglomerates of pseudohexagonal platelets, ruptured by attrition at grain joints followed by fracture leading to further fragmentation. During milling, progressive decrease in the intensity of the (002) peak of gibbsite in the powder X-ray diffraction pattern indicated amorphisation. It was found that the presence of hematite favoured amorphisation of gibbsite. The ζ potential and isoelectric point of gibbsite changed during milling, which indicated alteration of the gibbsite surface.

Pd‐Catalyzed Orthogonal Knoevenagel/Perkin Condensation–Decarboxylation–Heck/Suzuki Sequences: Tandem Transformations of Benzaldehydes into Hydroxy‐Functionalized Antidiabetic Stilbene–Cinnamoyl Hybrids and Asymmetric Distyrylbenzenes

Tandem reactions that involve chemoselective Knoevenagel/Perkin condensation-decarboxylation-Heck/Suzuki coupling or Heck-aldol sequences have been achieved. This enabled the first concise and efficient synthesis of several important hydroxy-functionalized compound classes, such as stilbene-cinnamoyl hybrids (potent protein tyrosine phosphatase1B inhibitors), cinnamoyl-cinnamic acid hybrids, asymmetric distyrylbenzenes, and biarylstyrenes. Previously reported synthesis require multiple steps and protection/deprotection manipulations.

Nitrogen-Metabolizing Enzymes: Effect of Nitrogen Sources and Saline Irrigation

Abstract Indian mustard (Brassica juncea L. cv. RH-30) was grown under different types and levels of nitrogen (N) sources, i.e. nitrate, ammonical, and nitrate plus ammonical, at 40, 80, and 120 kg ha− 1 under green house conditions. The plants were salinized with 8 and 12 dSm− 1 at 35 and 55 days after sowing. A progressive inhibition of the activity of enzymes of N metabolism, i.e., nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH), was observed with increasing level of salinity. However, the magnitude of such reductions was lowest at the highest level of N (120 kg ha− 1) as compared with the lowest level (40 kg ha− 1) irrespective of N source. The activity of nitrate-assimilating enzymes (NR and NiR) was maximum with nitrate fertilizer, and minimum with the ammonical form. The alleviation of detrimental effects of salinity on NR and NiR was better with the highest level of N (120 kg ha− 1) in nitrate form as compared with the lowest level of N (40 kg ha− 1). In contrast, the maximum activity of ammonium-assimilating enzymes (GS, GOGAT, and GDH) was observed with the highest level of N (120 kg ha− 1) and the minimum with the nitrate form of N under salinity. These results indicate that despite the high salinity, an increase in the concentration and uptake of N stimulates the activities of nitrate-assimilating enzymes (NR and NiR) as well as of the ammonia-assimilating enzymes (GS, GOGAT, and GDH).

Facile synthesis of 4-vinyl- and 4-fluorovinyl-1,2,3-triazoles via bifunctional “click-olefination” reagents

Modular synthesis of vinyl and fluorovinyl triazoles can be achieved from bifunctional propargyl and fluoropropargyl sulfones by Cu-catalyzed azide-alkyne ligation and Julia-Kocienski olefination. Competitive click reactions of the protio and fluoropropargyl sulfones show higher reactivity of the latter, and a preliminary DFT analysis was performed.

Flax fibre reinforced polylactic acid composites with amphiphilic additives

Abstract Biocomposites were successfully prepared by reinforcing polylactic acid with flax fibres (PF). To improve the interfacial adhesion between the matrix and the fibres, amphiphilic compounds as additives were introduced. Structural and thermal characterisations of the PF were performed by Fourier transform infrared spectra, differential scanning calorimetry and thermogravimetric analysis. The interfacial adhesion between the fibres and the matrix was visually assessed from the SEM images of fractured specimens. Dynamic mechanicalthermal analysis was performed to evaluate the damping behaviour of the composites and thereby to interpret the interfacial adhesion between fibres and the matrix. It was observed that in the case of mandelic acid, particles/spheres were generated, resulting in effective stress transfer from the matrix resins to flax fibres, thereby increasing the storage modulus and impact strength of the composites. Mechanical properties and the water uptake of the composites with amphiphilic additives have also been reported.