Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations at the UB3LYP/6-31G(d) level have been performed to investigate the tunable nature, i.e., doping and dedoping processes, of polypyrrole (PPy). The calculated theoretical data show strong correlation with the recent experimental reports, which validates our computational protocol. The calculated properties are extrapolated to the polymer (PPy) through a second-order polynomial fit. Changes in band gap, conductivity, and resistance of nPy and nPy-X (where n = 1–9 and X = +, NH3, and Cl) were studied and correlated with the calculated vibrational spectra (IR) and electronic properties. Upon doping, bridging bond distance and internal bond angles decrease (decrease in resistance over polymer backbone), whereas dedoping results in increases in these geometric parameters. In the vibrational spectrum, doping is characterized by an increase in the band peaks in the fingerprint region and/or red shifting of the spectral bands. Dedoping (9Py+ with NH3), on the other hand, results in decreases in the number of vibrational spectral bands. In the UV–vis and UV–vis–near-IR spectra, the addition of different analytes (dopant) to 9Py results in the disappearance of certain bands and gives rise to some new absorbances corresponding to localized and delocalized polaron bands. Specifically, the peaks in the near-IR region at 1907 nm for Py+ and 1242 nm for 9Py-Cl are due to delocalized and localized polaron structures, respectively. Upon p-doping, the band gaps and resistance of nPy decrease, while its conductivity and π-electron density of conjugation increase over the polymeric backbone. However, a reversal of properties is obtained in n-doping or reduction of nPy+. In the case of oxidation and Cl dopant, the IP and EA increase, and consequently, there is a decrease in the band gap. NBO and Mulliken charges analyses indicate charge transferring from the polymer in the case of p-type dopants, while this phenomenon is reversed with n-type dopants.

Density functional theory studies (DFT) have been carried out to evaluate the ability of polyaniline emeraldine salt (PANI ES) from 2 to 8 phenyl rings as sensor for NH 3 , CO 2 , and CO. The sensitivity and selectivity of nPANI ES among NH 3 , CO 2 , and CO are studied at UB3LYP/ 6-31G(d) level of theory. Interaction of nPANI ES with CO is studied from both O (CO(1)) and C (CO(2)) sides of CO. Interaction energy, NBO, and Mulliken charge analysis were used to evaluate the sensing ability of PANI ES for different analytes. Interaction energies are calculated and corrected for BSSE. Large forces of attraction in nPANI ES-NH 3 complexes are observed compared to nPANI ES−CO 2 , nPANI ES-CO(1), and nPANI ES-CO(2) complexes. The inertness of + CO − in nPANI ES-CO(1) and nPANI ES-CO(2) complexes are also discussed. Frontier molecular orbitals and energies indicate that NH 3 changes the orbital energy of nPANI ES to a greater extent compared to CO 2 , CO(1), and CO(2). Peaks in UV−vis and UV−vis−near-IR spectra of nPANI ES are blue-shifted upon doping with NH 3 , CO 2 , CO(1), and CO(2) which illustrates dedoping of PANI ES to PANI emeraldine base (PANI EB).Finally, it is concluded that PANI ES has greater response selectivity toward NH 3 compared to CO 2 and CO and it is consistent with the experimental observations.

Carbon nanotubes (CNTs) are known as nano-architectured allotropes of carbon, having graphene sheets that are wrapped forming a cylindrical shape. Rolling of graphene sheets in different ways makes CNTs either metals or narrow-band semiconductors. Over the years, researchers have devoted much attention to understanding the intriguing properties CNTs. They exhibit some unusual properties like a high degree of stiffness, a large length-to-diameter ratio, and exceptional resilience, and for this reason, they are used in a variety of applications. These properties can be manipulated by controlling the diameter, chirality, wall nature, and length of CNTs which are in turn, synthesis procedure-dependent. In this review article, various synthesis methods for the production of CNTs are thoroughly elaborated. Several characterization methods are also described in the paper. The applications of CNTs in various technologically important fields are discussed in detail. Finally, future prospects of CNTs are outlined in view of their commercial applications.

Graphical abstractPromising antileishmanial properties were observed with Sargentodoxa cuneata mediated Ag and AuNPs. This study opens a platform for the synthesis new leishmanicidal agents AbstractLeishmaniasis remains one of the fatal diseases worldwide and the conventional antileishmanial therapies are associated with several drawbacks. Therefore, there is a need to develop new antileishmanial strategies. Biogenic silver and gold nanoparticles possess broad-spectrum antimicrobial activities and could be future alternative to current antimicrobial agents. In this report, we present a simple and green approach to synthesize silver and gold nanoparticles with efficient biological activities. Phytochemicals from Sargentodoxa cuneata were used to reduce and stabilize the silver and gold ions into metallic nanoparticles. The synthesized nanoparticles were characterized by UV-visible spectroscopy (surface plasmon resonance), X-ray diffraction analysis (crystallinity), High-resolution transmission electron microscopy (size and morphology), energy dispersive X-ray (elemental composition) and FTIR (surface functionalities). Under the optimized conditions, the synthesized silver nanoparticles were spherical in shape, small size (3-8 nm) and well dispersed. However, the gold nanoparticles were mostly hexagonal in shapes with approximate size from 15 to 30 nm. Promising antileishmanial activity was shown by silver and gold nanoparticles with an IC 50 value of 4.37 and 5.29 µg/mL respectively. Silver nanoparticles also exhibited significant antibacterial activity against Staphylococcus aureus (32 ± 3 mm), Pseudomonas araginosis (16 ± 2 mm), and Bacillus subtilis (18 ± 2 mm). The depicted biological activities of nanoparticles are not simply due to the capped silver and gold atoms but also to their surface macromolecules. Thus, the use of Sargentodoxa cuneata as reducing and capping agent will retain its biological activities even after the depletion of maintained silver and gold. The findings of this study indicate that, these nanoparticles could be an alternative, safe, and effective source of antileishmanial agents. 4 assay, and capillary electrophoresis 9-12 . These nanostructures upon cellular uptake behave as thermal scalpels to kill the infected cell 13,14 .Silver is a promising agent possessing broad spectrum antibacterial activity with minimum chance of bacterial resistance to it 15 . It has been published that silver ions interfere with bacterial DNA replication, disrupt cell membrane, inhibit critically important enzymes and damage bacteria by a process called respiratory burst mechanism 16-18 . Furthermore, silver and gold nanoparticles have the ability to produce reactive oxygen species (ROS), which play an important role in killing pathogenic microbes. It has been reported that leishmania parasites are highly sensitive to ROS 19 . In order to kill leishmania parasite by a treatment that involve reactive species, a continuous supply of these oxygen species can be ensured with the use of noble metal nanoparticles...

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