Synthesis of metallic nanoparticles using biometabolites: mechanisms and applications.

Bio-metabolites have played a crucial role in the recent green synthesis of nanoparticles, resulting in more versatile, safer, and effective nanoparticles. Various primary and secondary metabolites, such as proteins, carbohydrates, lipids, nucleic acids, enzymes, vitamins, organic acids, alkaloids, flavonoids, and terpenes, have demonstrated strong metal reduction and stabilization properties that can be utilized to synthesize nanomaterials and influence their characters. While physical and chemical methods were previously used to synthesize these nanomaterials, their drawbacks, including high energy consumption, elevated cost, lower yield, and the use of toxic chemicals, have led to a shift towards eco-friendly, rapid, and efficient alternatives. Biomolecules act as reducing agents through deprotonation, nucleophilic reactions, transesterification reactions, ligand binding, and chelation mechanisms, which help sequester metal ions into stable metal nanoparticles (NPs). Engineered NPs have potential applications in various fields due to their optical, electronic, and magnetic properties, offering improved performance compared to bulkier counterparts. NPs can be used in medicine, food and agriculture, chemical catalysts, energy harvesting, electronics, etc. This review provides an overview of the role of primary and secondary metabolites in creating effective nanostructures and their potential applications.

Impact of carbon quantum dots on self-assembly and dielectric relaxation modes of a room temperature tri-component fluorinated antiferroelectric liquid crystal mixture.

We investigated the impact of carbon quantum dots (CQDs) of sizes ∼2-5 nm in a room temperature tri-component fluorinated antiferroelectric liquid crystal (AFLC) mixture. The synthesised CQDs have been characterised by high-resolution transmission electron microscopy and X-ray diffraction spectroscopy. An increase in the transition temperature and enthalpy to the isotropic liquid phase indicates stabilization of the AFLC mixture in the presence of CQDs. The dielectric studies have been carried out in the frequency range of 1 Hz-40 MHz under the planar anchoring conditions of the molecules. An appreciable increase in the permittivity, dielectric strength, and conductivity has been observed owing to the existence of sp2/sp3 hybridization in the CQDs which form a strong coupling and develop a dipolar ordering in the systems. Various relaxation frequencies were increased with the incarceration of CQDs in the AFLC mixture. Overall, the different studies suggest that the doped CQDs are very well settled in between the host molecules without disturbing the molecular ordering of the hosts. Such results are encouraging and reveal the potential applicability of the CQD doped systems to produce highly efficient tuneable optical devices and other multifaceted applications.

Phytosynthesis of Silver Nanoparticles Using Oscimum sanctum Leaf Extract and Studies on Its Antidiabetic, Antioxidant, and Antibacterial Properties.

The green synthesis of plasmonic metal nanoparticles (NPs) has gained considerable attention among researchers as it is cost-effective, environmentally friendly, energy-saving, and nontoxic. We have synthesized silver NPs (Ag NPs) with Oscimum sanctum (holy Tulsi) medicinal plant leaf extract by green synthesis methods. Further, we investigate the antibacterial, antioxidant, and antidiabetic activities of the synthesized Ag NPs. Oscimum sanctum leaf extract has secondary metabolites such as phenolic and flavonoid compounds, which play a significant role in the synthesis of Ag NPs. Subsequently, these bioactive molecules get adsorbed on the large surfaces of the synthesized NPs. Spectroscopic techniques such as X-ray diffraction (XRD), UV-visible absorption, Fourier-transform infrared, and scanning electron microscopy have been used to study and characterize the phytosynthesized Ag NPs. The XRD pattern confirms the formation of crystalline Ag NPs with a high degree of intensity. UV-visible absorption spectra confirm the surface plasmon resonance peak in the range of 440-450 nm. A scanning electron microscopy picture reveals homogeneous growth of Ag NPs with particle sizes of 200-400 nm; however, crystallite size along different planes has been estimated in the range of 18-23 nm. We have found that these Ag NPs synthesized with Oscimum sanctum leaf extract show inhibitory activity against α-amylase and α-glucosidase enzymes in vitro. Our findings further reveal that these Ag NPs are more effective in inhibiting the growth of Salmonella typhi bacteria as compared to other bacterial strains.

Enhancement of dielectric and electro-optical characteristics of liquid crystalline material 4'-octyl-4-cyano-biphenyl with dispersed functionalized and nonfunctionalized multiwalled carbon nanotubes.

For recent applications, liquid crystal-carbon nanotube based nanocomposite systems have been proven to be highly attractive. In this paper, we give a thorough analysis of a nanocomposite system made of both functionalized and nonfunctionalized multiwalled carbon nanotubes that are disseminated in a 4'-octyl-4-cyano-biphenyl liquid crystal medium. Thermodynamic study reveals a decrease in the nanocomposites' transition temperatures. In contrast to nonfunctionalized multiwalled carbon nanotube dispersed systems, the enthalpy of functionalized multiwalled carbon nanotube dispersed systems has increased. In comparison to the pure sample, the dispersed nanocomposites have a smaller optical band gap. A rise in the longitudinal component of permittivity and, consequently, the dielectric anisotropy of the dispersed nanocomposites has been observed by dielectric studies. When compared to the pure sample, the conductivity of both dispersed nanocomposite materials has increased by two orders of magnitude. For the system with dispersed functionalized multiwalled carbon nanotubes, the threshold voltage, splay elastic constant, and rotational viscosity all decreased. For the dispersed nanocomposite of nonfunctionalized multiwalled carbon nanotubes, the value of the threshold voltage is somewhat decreased but the rotational viscosity and splay elastic constant both are enhanced. These findings show the applicability of the liquid crystal nanocomposites for display and electro-optical systems with appropriate tuning of the parameters.

Gold Nanorod-Induced Effects in a Mesogenic Compound 4-(trans-4-n-Hexylcyclohexyl) isothiocyanatobenzene.

Gold nanorods (GNRs) have a capsule-like structure with different optical properties than spherical gold nanoparticles due to surface plasmon resonance. Liquid crystals (LCs) are mesogenic compounds having crystal-like orientation and liquid-like fluidity. They are important materials from a technological point of view. Both GNRs and LC compounds are anisotropic in shape and properties. Different nano entities show interesting results when dispersed in different liquid crystalline materials which are instrumental from the application point of view. In the present work, GNRs have been dispersed in nematic liquid crystalline materials, namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzene (6CHBT). Calorimetric, texture, spectroscopic, and dielectric studies were carried out for a pure 6CHBT and its composites with GNRs. Different calorimetric and dielectric parameters such as transition temperature, enthalpy, heat flow, permittivity, dielectric strength, dielectric anisotropy, and relaxation frequency have been determined, and the effect of GNRs has been explored. This article gives an insight into the influence of GNRs on the morphology and anisotropic physical properties of the nematic liquid crystalline material.

Magnified charge carrier conduction, permittivity, and mesomorphic properties of columnar structure of a room temperature discotic liquid crystalline material due to the dispersion of low concentration ferroelectric nanoparticles.

Liquid crystal nanocomposites have been a hot topic of research due to optimization of physical properties with such blending. There are several reports on enhancement of physical properties of nematic liquid crystals due to the blending of the nanomaterials. L. M. Lopatina and J. V. Selinger [Phys. Rev. Lett. 102, 197802 (2009)]10.1103/PhysRevLett.102.197802 have even proposed a theory based on experimental results for the enhancement of the properties of the nematic mesophase in the presence of ferroelectric nanoparticles. However, discotic liquid crystal nanocomposites are less studied. In the present experimental work, we have studied the effect of ferroelectric (BaTiO_{3}) nanoparticles on a room temperature discotic liquid crystalline material, namely 1,5-dihydroxy-2,3,6,7-tetrakis(3,7-dimethyloctyloxy)-9,10-anthraquinone. We investigated the physical properties of low concentration ferroelectric nanoparticle dispersed discotic columnar structure, using calorimetric, optical, x-ray diffraction, and dielectric spectroscopy tools. Results show that inclusion of ferroelectric nanoparticles in the discotic matrix consolidates the stability of the columnar matrix of the Col_{h} phase by virtue of their ferroic nature. An enhancement in charge carrier conductivity by several orders of magnitude at ambient conditions has been observed which makes such systems highly appropriate for one-dimensional conductors. Low concentration of BaTiO_{3} nanoparticles substantially enhanced permittivity of the system also. A molecular relaxation mode has been observed in the middle frequency range of the dielectric spectra. Enhancement of these important parameters could be possible due to the ferroelectric nature of the dispersed nanoparticles.