Spectral investigations on 1,4-dimethylamino anthraquinone under laser excitation

Surface enhanced Raman spectrum of 1,4-dimethylamino anthraquinone (1,4-DMAAQ) adsorbed on silver particles has been analyzed to understand the interaction between the molecule and silver surface. By studying the band intensities, the orientation of the molecule is determined. The high intensity and frequency downshifted peak due to carbonyl stretching vibration plays a major role, which shows that the molecules are chemisorbed through coordinating sites. The new peaks observed due to C-N and N-H stretching vibrations also provide the evidence for adsorption through co-ordinating sites. Optical absorption and laser induced fluorescence spectra of this molecule have also been studied in different solvents to understand the effect of environment. Polarization and anisotropy measurements provide the change in orientation induced by solvent molecules between absorption and emission transition dipoles.     

Elucidation of Binding Mechanism of Photodynamic Therapeutic Agent Toluidine Blue O with Chicken Egg White Lysozyme by Spectroscopic and Molecular Dynamics Studies

The nature of binding mechanism of toluidine blue O (TBO) with chicken egg white lysozyme was studied comprehensively by various spectroscopic and computational methods. Both steady state and time‐resolved fluorescence studies unambiguously point to the prevalence of static quenching mechanism in lysozyme–TBO system. Thermodynamic parameters revealed that the association of TBO with lysozyme was a spontaneous process in which hydrophobic and hydrogen bond interactions played a pivotal role in the binding process. The secondary and tertiary conformational changes of lysozyme in the presence of TBO were unraveled using absorption, Fourier transform infrared spectroscopy (FT‐IR) and circular dichroism (CD) techniques. Molecular docking studies of lysozyme–TBO system substantiated the findings of site marker experiment and revealed TBO adjacent to Trp‐63 and Trp‐108 residues of lysozyme. Molecular dynamics (MD) simulation studies of lysozyme–TBO system indicate a stable and effective complexation of TBO with lysozyme. It is hoped that the results presented here will enable further understanding of TBO toxicity.     

Green Synthesized Gold Nanoparticles as a Probe for the Detection of Fe3+ Ions in Water

Pure water which is free of toxic chemicals is necessary for human health. So, detection and control of heavy metal ions in water is very important. Keeping this in mind, selective and sensitive optical sensor based on surface plasmon resonance for detection of various heavy metals in water using gold nanoparticles was explained in this present study. These AuNPs were prepared using Hibiscus cannabinus leaf extract as reducing agent with the average particle size of 22 nm. These gold nanoparticles are considerably selective and sensitive towards Fe³⁺ and it was used to detect the concentration of Fe³⁺ ions in water in the range 29.82–173.74 μM by tracking the absorbance changes of SPR band and the sensitivity of the system towards the Fe³⁺ concentration and it was found to be 0.0037 μM^?1. We hope that these gold nanoparticles can be used for detecting Fe³⁺ ions concentration, in the water purification processes.     

Synthesis and Characterization of Silver–PVA Nanocomposite for Sensor and Antibacterial Applications

Silver–polyvinyl alcohol (PVA) nanocomposite is synthesized by a simple chemical reduction method in aqueous media and characterized by various techniques such as UV–Visible spectroscopy, transmission electron microscopy, X-ray diffraction and infrared spectroscopy. The morphology of the obtained silver nanoparticles is spherical in shape with an average diameter of 24 nm. The prepared silver–PVA nanocomposite is demonstrated to detect the concentration of heavy metal contaminant cadmium in water based on linear change in surface plasmon resonance absorption strength. The antibacterial tests show the inhibiting action of this nanocomposite against pathogenic bacteria Escherichia coli and Pseudomonas aeruginosa (gram negative), Bacillus cereus and Staphylococcus aureus (gram positive), which are found commonly in water. These observed optical and antibacterial properties, suggest the possible utilization of prepared silver–PVA nanocomposite in the water purification application.     

Impact of the Chirality and Curvature of Carbon Nanostructures on Their Interaction with Aromatics and Amino Acids

Understanding noncovalent interactions on the surfaces of carbon nanostructures (CNSs) is of fundamental importance and also has implications in nano‐ and biotechnology. The interactions of aromatic compounds such as benzene, naphthalene, and aromatic amino acids with CNSs of varying diameter, chirality, and curvature were systematically explored by using density functional theory. Planar graphene exhibits stronger binding affinity than curved carbon nanotubes (CNTs), whereas zigzag CNTs appear to show stronger binding affinity than armchair CNTs. For hydrocarbons, there exist two competing modes, namely, π–π stacking interactions and CH ??? π interactions, which bring the aromatic motifs into parallel and perpendicular dispositions with respect to the CNSs, respectively. Our results reveal that π–π stacking interactions override CH ??? π interactions in such cases. However, in the case of aromatic amino acids, π–π interactions can exist simultaneously along with a range of other interactions, including CH ??? π. The polarizability and HOMO energy of the CNSs were found to be the key factors that determine the binding energies. The HOMO–LUMO energy gaps of the CNSs were found to be undisturbed by the noncovalent functionalization of the aromatic molecules.     

Liquid crystal-gold nanoparticle composite-modified indium tin oxide (ITO) substrates and their electrochemical characterisation

A simple efficient strategy for the simultaneous synthesis and anchoring of liquid crystal (LC)-stabilised gold nanoparticles (NPs) on indium tin oxide (ITO) substrate is described. A monolayer of 3-mercaptopropyltrimethoxy silane (MPS) compound was formed on ITO and quality of the monolayer was assessed using electrochemical techniques namely cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Gold NP preparation was carried out on this monolayer-modified substrate (and on bare ITO), in a single-step reaction, simply by drop-casting a solution containing an appropriate amount of chloroauric acid and a LC compound possessing a terminal amino group, on the MPS monolayer-modified substrate and heating (70degree) for 2-3 min.. The LC compound served as a reducing agent as well as a capping ligand. LC-capped NPs were chemically anchored onto the ITO substrate through bonding to thiol moiety of the MPS. The CV and EIS analysis of the MPS monolayer showed a complete blocking behaviour for the electron transfer across the electrode/electrolyte interface confirming the formation of a high-quality dense compact monolayer. On the other hand, upon immobilisation of LC-gold NP composite on self-assembled monolayer-modified ITO substrates, both CV and impedance studies showed a small current indicating the gold NP-mediated electron transfer, thus confirming the successful immobilisation of NPs.     

Fourier transformed infrared spectral investigations of molecular interactions in propionic acid–2-propanol binary system

FTIR spectra of propionic acid (PA), 2-propanol (PROH) and its binary mixtures with varying molefraction of the PA were recorded in the region 500–3500 cm^?1, to investigate the formation of hydrogen bonded complexes in a mixed system. The observed features in ν(CO), ν(CO) and δ(COH) of PA, ν(CO) of PROH and δ(COH) of PA + PROH have been explained in terms of the hydrogen bonding interactions between PROH and PA and dipole–dipole interaction. The dipole moment derivative for the above mentioned vibrational modes have also been predicted from the integrated absorbance. The intrinsic linewidth for the vibrational modes ν(CO) and δ(COH) of PA has been elucidated using Bondarev and Mardaeva model.     

Spectral Investigations of Solvatochromism and Preferential Solvation on 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone

Solvatochromic and preferential solvation of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Optical absorption spectra of DHDMAQ in different solvents show the intra molecular charge transfer band in the region 400–550nm. The observed blue shift with solvent polarity indicates the delocalisation of the excited state, owing to reduction in quasiaromaticity of the chelate rings formed by intra molecular hydrogen bonds, due to electrostatic or hydrogen bonding interaction. This is also confirmed by the observed low oscillator strength and the transition dipole moment. The observed quantum yield of DHDMAQ in different solvents is due to the inter molecular hydrogen bond in the excited state in addition to the intra molecular hydrogen bond. It also reveals from the low oscillator strength, which indicates that the radiative decay is low. Excited state dipole moment of DHDMAQ is calculated by solvatochromic data and it shows a lower value than ground state dipole moment. The preferential solvation parameter shows that in dimethyl formamide (DMF) + ethanol mixture, the DHDMAQ is preferentially solvated by ethanol in DMF rich region and by DMF in ethanol rich region. In the case of DMF + dichloromethane mixture DHDMAQ is preferentially solvated by DMF.     

Glutathione Functionalized Gold Nanoparticles as Efficient Surface Enhanced Raman Scattering Substrate for Poly Chlorinated Biphenyl Detection

Polychlorinated biphenyls (PCBs) are harmful even at trace level in the environment, and they are difficult to detect. This work presents a simple method for preparation of glutathione (GSH) functionalized gold nanoparticles (Au NPs) (GSH-Au NPs) for the detection of PCBs and its isomers based on surface enhanced Raman scattering (SERS). The prepared Au NPs show the surface plasmon band around 533 nm. The crystallinity and formation of GSH-Au NPs were confirmed by using X-ray diffraction and vibrational studies. Transmission electron microscopic analysis showed the average particle size of GSH-Au NPs is around 16 nm. The morphology of the GSH-Au NPs indicates dumbbell-shaped structures with “hot spots” present. These hot spots increase the SERS activity significantly. Gas chromatography–mass spectrum showed that the soil extract contained PCBs, which, has also been detected using SERS. SERS based detection is simple and powerful for identifying the PCBs, as established here for PCBs in the real soil sample.Hence, from this investigation, a rapid, sensitive, cost-effective sensing method for detecting toxic PCBs in the environment was demonstrated.     

Novel Bis(1,2,4-oxadiazolyl) Fused Thiazole Derivatives: Synthesis and Anticancer Activity

A novel series of bis-1,2,4-oxadiazole fused benzothiazole derivatives 9a–9j are synthesized, and their structures are confirmed by ¹H and ¹³C NMR, and mass spectral data. All products are evaluated in vitro for their anticancer potential against a panel of four human cancer cell lines such as lung cancer (A549), breast carcinoma (MCF-7), melanoma (A375), and colon cancer (HT-29). The combretastatin-A4 is used as standard drug. All compounds 9a–9j exhibit significant anticancer activity with IC₅₀ values ranging from 0.11±0.01 to 14.6±3.89 μM. Among these, compounds 9a–9d, 9h, 9i demonstrate more potent activity than the control.