<p>In this work, a simple, less time consuming electrochemical method in the form of an electrochemical sensor has been developed for the detection of PAHs. The sensor was fabricated by the deposition of silver-gold (1:3) alloy nanoparticles (Ag-AuNPs) on ultrathin overoxidized polypyrrole (PPyox) film which formed a PPyox/Ag-AuNPs composite on glassy carbon electrode (PPyox/Ag-AuNPs/GCE). The silver-gold alloy nanoparticles deposited to form the composite were chemically prepared by simultaneous reduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) using sodium citrate and characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the alloy nanoparticles.</p>

The mechanisms of pre-mRNA splicing regulation are poorly understood. Here we dissect how the Saccharomyces cerevisiae ribosomal L30 protein blocks splicing of its pre-mRNA upon binding a kink-turn structure including the 5' splice site. We show that L30 binds the nascent RPL30 transcript without preventing recognition of the 5' splice site by U1 snRNP but blocking U2 snRNP association with the branch site. Interaction of the factors BBP and Mud2p with the intron, relevant for U2 snRNP recruitment, is not affected by L30. Furthermore, the functions of neither the DEAD-box protein Sub2p in the incipient spliceosome, nor of the U2 snRNP factor Cus2p on branch site recognition, are required for L30 inhibition. These findings contrast with the effects caused by binding a heterologous protein to the same region, completely blocking intron recognition. Collectively, our data suggest that L30 represses a spliceosomal rearrangement required for U2 snRNP association with the nascent RPL30 transcript.

<p>In this work, a simple, less time consuming electrochemical method in the form of an electrochemical sensor has been developed for the detection of PAHs. The sensor was fabricated by the deposition of silver-gold (1:3) alloy nanoparticles (Ag-AuNPs) on ultrathin overoxidized polypyrrole (PPyox) film which formed a PPyox/Ag-AuNPs composite on glassy carbon electrode (PPyox/Ag-AuNPs/GCE). The silver-gold alloy nanoparticles deposited to form the composite were chemically prepared by simultaneous reduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) using sodium citrate and characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the alloy nanoparticles.</p>

Magister Scientiae - MSc / Polyaromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that have been shown to be teratogenic, mutagenic and carcinogenic and pose serious threats to the health of aquatic and human life. Several methods have been developed for their determination such as immunoassay, gas chromatography and high performance liquid chromatography (HPLC) in combination with fluorescence or absorbance detection. However, these methods are known to manifest underlying disadvantages such as complicated pretreatment, high costs and time consuming processes. In this work, a simple, less time consuming electrochemical method in the form of an electrochemical sensor has been developed for the detection of PAHs. The sensor was fabricated by the deposition of silver-gold (1:3) alloy nanoparticles (Ag-AuNPs) on ultrathin overoxidized polypyrrole (PPyox) film which formed a PPyox/Ag-AuNPs composite on glassy carbon electrode (PPyox/Ag-AuNPs/GCE). The silver-gold alloy nanoparticles deposited to form the composite were chemically prepared by simultaneous reduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) using sodium citrate and characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the alloy nanoparticles. Transmission electron microscopy showed that the synthesized nanoparticles were in the range of 20-50 nm. The properties of the composite formed upon deposition of the nanoparticles on the PPyox film were investigated by electrochemical methods. The PPyox/Ag-AuNPs/GCE sensor showed strong catalytic activity towards the oxidation of anthracene, phenanthrene and pyrene, and was able to simultaneously detect anthracene and phenanthrene in a binary mixture of the two. The catalytic peak currents obtained from square wave voltammetry increased linearly with anthracene, phenanthrene and pyrene concentrations in the range of 3.0 x 10-6 to 3.56 x 10-4 M,3.3 x 10-5 to 2.83 x 10-4 M, 3.3 x 10-5 to 1.66 x 10-4 M and with detection limits of 0.169 μM, 1.59 μM and 2.70 μM, respectively. The PPyox/Ag-AuNPs/GCE sensor is simple, has antifouling properties and is less time consuming with a response time of 4 s. / South Africa

Metal ion contamination in surface and ground water is a major threat as it has a direct implication on the health of terrestrial and aquatic flora and fauna. Lead (Pb2+), mercury (Hg2+), cadmium (Cd2+), nickel (Ni2+), copper (Cu2+) and cobalt (Co2+) are few of these metal ions which are classified under the high risk category. Of these, lead and mercury are of greater concern, as even nanomolar concentrations can be lethal, as they can be bio-accumulated and result in physiological as well as neurological disorders. In Asian countries like India and China, heavy metal pollution is more prevalent, as a consequence of poor governmental policies or ineffective or inadequate measures to combat this problem. In recent times, the monitoring and assessment of water pollution is a critical area of study, as it has a direct implication for its prevention and control. The major techniques used for metal ion detection are atomic absorption spectroscopy (AAS), X-ray fluorescence, ion chromatography, neutron activation, etc. Alternatively, the electrochemical, optical and electrical methods provide a platform for the fabrication of portable devices, which can facilitate the on-site analysis of samples in a rapid and cost-effective manner. This has led to a new field of research called chemical sensors or chemo sensory devices. The main aim of this study is to develop various chemosensory materials and test their response towards metal ion sensing. In this study, electroactive polymers have been synthesized for various sensor applications. The focus has been to design synthesize and test various functionalized electroactive polymers (FEAP) for the development of electrochemical, optical and chemoresistive sensors. Electroactive polymers like polyaniline, polypyrrole, polypyrrole grafted to exfoliated graphite oxide and dipyrromethene conjugated with p-(phenylene vinylene) have been synthesized and evaluated after functionalizing with metal coordinating ligands. These metal coordinating ligands were selected, in order to enhance their metal uptake capacity. Various metal ligands like imidazole, tertiary amine group, iminodiacetic acid, and dipyrromethene incorporated either in the polymer backbone or as a part of the backbone have been chosen for the metal binding. These functionalized electroactive polymers (FEAP) served as active material for metal ion sensing. The present investigation is subdivided into three sections. The first part includes design and chemical synthesis of the functionalized polymers by a series of organic reactions. The synthesis has been followed up by characterization using spectroscopic methods including NMR, FTIR, GCMS and Mass spectrometry. In the second part of the investigation, the synthesized polymer has been characterized for the changes in electronic, electric and optical properties after interaction with the selected metal ions. For this, the FEAP is allowed to interact with various metal ions and the changes in the relevant properties have been measured. This includes the study of changes in the conductivity, electronic properties like absorption or emission of the polymer, changes in the redox properties, etc. The third phase of investigation deals with the fabrication of the devices using the active FEAP. The sensor devices comprised of either films, or electrode modified with FEAP or solution of the FEAP, in combination with an appropriate technique has been used for the sensing. The major objectives are enumerated below 1. Functionalzation of polyaniline with imidazole functional group to get imidazole functionalized polyaniline (IMPANI) and study of the electronic, electrical and optical properties of the same. 2. Preparation of films of IMPANI and study of the change in conductivity of the film upon interaction with various metal ions, namely Cu2+, Co2+ and Ni2+ in their chloride form. 3. Synthesis of amine functionalized aniline monomer and chemical graft polymerization onto exfoliated graphite oxide as a substrate to synthesise the amine funtionalised polyaniline grafted to exfoliated graphite oxide (EGAMPANI). Modification of the carbon paste electrode (CPE) with EGAMPANI and study of the electrode characteristic. 4. Study of the electrode properties of EGAMPANI modified carbon paste electrode. 5. Evaluation of the EGAMPANI modified carbon paste electrode as a multi-elemental voltammetric sensor for Pb2+, Hg2+ and Cd2+ in aqueous system. 6. Functionalization of polypyrrole with iminodiacetic acid and characterization of the polymer to synthesis iminodiacetic acid functionalized polypyrrole (IDA-PPy). 7. Modification of the CPE with IDA-PPy by drop casting method and evaluation of the Pb2+ sensing properties. 8. Study of the effect of other metal ions say Hg2+, Co2+, Ni2+, Zn2+, Cu2+ and Cd2+ on the anodic stripping current of Pb2+ using EGAMPANI modified CPE. 9. Synthesis of dipyrromethene-p-(phenylene vinylene) conjugated polymer for heavy metal ion sensing. 10. Study of the changes in the optical absorption and emission properties of the polymer in THF and evaluation of the change in these optical properties upon interaction with the metal ions as analyte. The salient findings of the research work are highlighted as follows, In the first synthesis, aniline has been functionalized with imidazole group and this monomer has been chemical oxidatively polymerized to obtain imidazole functionalized polyaniline (IMPANI). The synthesized polymer possesses a nano-spherical structure, as confirmed from the morphological characterisation using scanning electron microscopy. The IMPANI has been interacted with a representative metal ion, copper (II) chloride, and the copper complexed polymer (Cu-IMPANI) has been subjected to various studies. The coordination of copper with IMPANI results in an increase of molecular weight of the polymer as a result of aggregation, as observed from dynamic light scattering measurements. Apart from this, a significant finding is the decrease of the pH of the system after copper ion coordination attesting to the generation of a secondary hydrochloride ion during the coordination of the copper to the imidazole side chain. This is further confirmed by an increase in conductivity of the Cu-IMPANI compared to IMPANI, measured using the four-probe technique. The increase of conductivity due to copper coordination is one order of magnitude higher. The films which have been prepared from IMPANI and Cu-IMPANI exhibit different morphology. The Cu-IMPANI film prepared by prior co-ordination of Cu ion with IMPANI powder shows a flaky structure, which is not preferable for the conductivity measurements, as a consequence of discontinuity in the medium. To overcome this problem, IMPANI films were initially prepared and then interacted with copper ions for a desired duration, before measurement of the conductivity. This latter procedure enabled the preparation of smooth films for the development of chemoresistive sensors. In continuation of the initial study highlighted above, IMPANI films of thickness 0.02 ± 0.001 mm have been prepared using IMPANI and PANI in DMPU in the ratio of 7:3 by mass. After exposure of the films with respective metal chlorides, such as Ni2+, Co2+ and Cu2+, a change in conductivity is observed in the concentration range of 10-2 to 1 M of metal chlorides. The sensor response may be arranged in the sequence: Ni2+ > Cu2+ > Co2+ at 1M concentration. On the contrary, films prepared from PANI-EB under identical conditions do not exhibit any appreciable change in conductivity. The optimum exposure time is determined to be 10 min for a maximum change in conductivity, after exposure to the chosen metal ions. In the second system taken up for investigation, a tertiary amine containing polyaniline (AMPANI) has been grafted to exfoliated graphite oxide. The amine containing polyaniline grafted to exfoliated graphite oxide (EGAMPANI) has been characterised for structural, morphological and elemental composition. The grafting percentage has been determined to be 7 % by weight of AMPANI on the EGO surface. The synthesized EGAMPANI (5 weight %) has been used to modify carbon paste electrode (CPE) for electrochemical sensor studies. Based on the differential pulse anodic stripping voltammetric studies, the electrochemical response may be arranged in the following sequence: Pb 2+>Cd 2+>Hg 2+ The minimum detection levels obtained are 5×10-6, 5×10-7, and 1.0×10-7 M for Hg2+, Cd2+ and Pb2+ ions respectively. In the next study, an iminodiacetic acid functionalized polypyrrole (IDA-PPy) has been synthesized and characterised for its elemental and structural properties. This has been further used to modify the CPE by drop casting method and used for the specific detection of Pb2+ in acetate buffer. Various parameters governing the electrode performance such as concentration of depositing solution, pH of depositing solution, deposition potential, deposition time, and scan rate, have been optimized to achieve maximum performance and found to be 20 μl, 4.5, -1.3 V, 11 min, 8 mV s-1 respectively for the chosen parameters. Additionally, the influence of other heavy metal ions on the lead response has been studied and it is observed that Co, Cu and Cd ions are found to be interfering. Further, the response of Cd, Co, Cu, Hg, Ni and Zn on IDA-PPy functionalized electrode has been evaluated. The selectivity of IDA-PPy modified electrode for Pb2+ is observed in the concentration range of 1 × 10-7 M and below. The IDA-PPy modified CPE shows a linear correlation for Pb2+ concentration in the range from 1×10-6 to 5×10-9 M and with a lowest limit of detection (LLOD) of 9.6×10-9 M concentration. The efficacy of the electrode for lead sensing has also been evaluated with an industrial effluent sample obtained from a lead battery manufacturing unit. The fourth synthesis pertained to the development of an optical sensor for Fe2+, and Co2+ ions. For this, dipyrromethene as a metal coordinating ligand in conjugation with p-phenylenevinylene has been synthesized and tested for its structural as well as optical properties. It is observed that the polymer shows three absorptions, namely at 294 nm, 357 nm and a major absorption observed as a broad band ranging from 484 to 670 nm. The emission spectrum of the polymer excited at 357 nm shows a characteristic blue emission with a maximum intensity centered at 425 nm. The emission quenching in the presence of various metal ions have been tested and are found to be quenched in presence of Fe2+ and Co2+ ions. All the other metal ions tested namely, Cr3+, Cu2+, and Zn2+ are not found to exhibit any change in the emission spectra below the concentration of 1 × 10-4 M. The linear correlation of the emission intensity with the concentration of the Co2+ and Fe2+ ions has been determined using Stern-Volmer plot. For Co2+ the Stern-Volmer regime is observed from 1×10-4 to 9×10-4 M concentration and the quenching constant Ksv is determined to be 8.67 ×103 M-1. For Fe2+, the linearity is found to be in the regime of 1×10-5 to 9×10-5 M and the quenching constant Ksv is determined to be 7.90 × 103 M-1. In conclusion, different electroactive polymers functionalized with metal coordinating ligands have been synthesized, characterised and evaluated for metal sensing applications. Techniques like electrochemical, optical and conductivity have been used to characterise the response of these FEAP towards metal sensing. It is can be concluded that the electrochemical sensors are more reliable for sensing especially at very low concentrations of metal ions such as Pb, Cd and other techniques like optical and conductimetric are good for detecting metal ions namely Fe, Co, Ni, Cu. The selectivity towards the metal ions is a function of the metal chelating ligand and the extent of sensitivity is dependent upon the technique employed.

With the discovery of conductivity in doped polyacetylene (PA), a new era in synthetic metals has emerged by breaking the traditionally accepted view that polymers were always insulating. Conducting polymers are essentially characterized by the presence of conjugated bonding on the polymeric back bone, which facilitates the formation of polarons and bipolarons as charge carriers. Among the numerous conducting polymers synthesized to date, polypyrrole (PPy) is by far the most extensively studied because of prodigious number of applications owing to its facile polymerizability, environmental stability, high electrical conductivity, biocompatibility, and redox state dependent physico-chemical properties. Electrochemically prepared PPy is more interesting than the chemically prepared polymer because it adheres to the electrode surface and can be directly used for applications such as supercapacitors, electrochemical sensors, electromechanical actuators and drug delivery systems. In quest for improvement in quality of the device performances in the mentioned applications, micro and nano structured polymeric materials which bring in large surface area are studied. Finding a simple and efficient method of synthesis is very important for producing devices of PPy microstructures. Till date, Hard and soft template methods are the most employed methods for synthesis of these structures. Soft template based electrochemical methods are better than hard template methods to grow clean PPy microstructures on electrode substrates as procedures for removal of hard templates after the growth of microstructures are very complex. As per the literature, there is no unique method available to grow PPy microstructures which can demonstrate several applications. Although gas bubble based soft template methods are exploited to grow conducting polymer microstructures of sizes in few hundreds of micrometers, studies on applications of the same are limited. Hence it is planned to develop procedures to grow microstructures that can be used in several applications. In the current work, PPy microstructures with high coverage densities are synthesized on various electrode substrates by soft template based electrochemical techniques. Hollow, hemispherical and spherical PPy microstructures are developed by a two step method using electro generated hydrogen bubble templates on SS 304 electrodes. In the first step, Hydrogen bubbles are electro generated and stabilized on the electrode in the presence of β- naphthalene sulfonic acid (β-NSA). In the second step, Pyrrole is oxidised over the bubble template to form PPy microstructures. Microstructures (open and closed cups) of average size 15 μm are uniformly spread on the surface with a coverage density of 2.5×105 units /cm2. Globular PPy microstructures are developed by a single step method using concomitantly electro generated oxygen bubble templates on SS 304 electrodes during electropolymerization. Microstructures of average size 4 μm are uniformly spread on the surface with a coverage density of 7×105 units/cm2. Surfactant properties of Zwitterionic 4-(2-hydroxyethyl)-1-piperazine ethane sulfonic acid (HEPES) are exploited for the first time to grow conducting polymer microstructures. Ramekin shaped PPy microstructures are developed using HEPES as the surfactant to stabilize hydrogen bubble templates in a two step electrochemical synthesis method. Microramekins of size 100 µm are uniformly spread on the surface with a coverage density of 3000 units/cm2. Micropipettes and microhorns of PPy are synthesised by a single step electrochemical route using HEPES as a surfactant. Hollow micropipettes of length 7 µm with an opening of 200 nm at the top of the structure are observed. Similarly microhorn/celia structures are observed with length 10-15 µm. Microcelia are uniformly distributed over the surface with each structure having a diameter of 2 µm at the base to 150 nm at the tip. Growth mechanism based on contact angle of the reactant solution droplets on the substrate is proposed. PPy microstructures are characterized by scanning electron microscopy, X-Ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman Spectroscopy and UV-Visible spectroscopy to study morphology, ‘chemical bonding and structure’ , ‘defects and charge carriers’. Applicability of the electrodes with PPy microstructures in supercapacitors is investigated by cyclic voltammetry, chronopotentiometry and electrical impedance spectroscopy. Electrodes developed by all the above methods demonstrated very good supercapacitance properties. Supercapacitor studies revealed very high specific capacitances (580, 915, 728 and 922 F/g,) and specific powers (20, 25, 13.89 and 15.91 kW/kg) for electrodes with PPy microstructures (H2 bubble based two step method, O2 bubble based single step method, HEPES stabilized H2 bubbble method and HEPES based microhorn/celia structures respectively). Supercapacitive behavior of all the electrodes is retained even after an extended charge-discharge cycling in excess of 1500 cycles. Horseradish peroxidase entrapped, bowl shaped PPy microstructures are developed for H2O2 biosensing. Amperometric biosensor has a performance comparable to the sensors reported in the literature with high sensitivity value of 12.8 μA/(cm2.mM) in the range 1.0 mM to 10 mM. Glucose oxidase entrapped PPy amperometric biosensor is developed for Glucose sensing. Sensitivity of 1.29 mA/(cm2.mM) is observed for β-D-Glucose sensing in the 0.1 mM to 5.0 mM range while 58 μA/(cm2.mM) is observed in the 5.0 to 40 mM range. Potentiometric urea sensor with urease entrapped PPy microstructures on SS electrode is developed. It is able to sense urea in the micromolar ranges down to 0.1 μM. It represented an excellent performance with sensitivity of 27 mV/decade. Sensitivity in the micromolar range is 4.9 mV/(μM.cm2). Drug encapsulation and delivery is successfully demonstrated by two actuation means (i) by electrochemical actuation, (ii) by actuation based on pH changes. Concepts are proved by delivering a fluorescent dye into neutral and acidic solutions. Drug delivery is confirmed by UV-Visible spectroscopy and Fluorescence microscopy. Finally, Micro/nanostructures with Tangerine, Hollow globular (Pani Poori), Chip, Flake, Rose, Worm, Horn and Celia shapes are synthesized electrochemically and scanning electron microscopic studies are presented. Controlled growth of microstructures on lithographically patterned gold interdigital electrodes is demonstrated with a future goal of creating addressable microstructures. The studies reported in the thesis provide an insight on various applications of PPy microstructures (supercapacitors, sensors and drug delivery systems) developed by a unique methodology based on electrochemically generated gas bubble templates.

No description available.

Conducting and semiconducting polymers, consisting of delocalized π-electrons, have been studied for the past three decades. These materials have shown novel physical properties with interesting applications in batteries, detectors, light emitting diodes, field effect transistors, solar cells, biosensors etc. Nevertheless the charge transport properties are yet to be understood in detail due to the complexity of the system, especially due to the interplay of quasi-one dimensionality (q-1D), disorder, localization and electron-electron interactions(EEI). A combined investigation of both conductivity and spin lattice relaxation time, especially at very low temperatures and high magnetic fields, is really lacking in conducting polymers. In this thesis a set of experiments – dc conductivity, magnetoresistance (MR), Nuclear Magnetic Resonance (NMR) spin lattice relaxation time (T1) measurements, magnetic susceptibility amd ac conductivity have been carried out in conducting polymers. NMR being a local probe it is possible to get the nanoscopic scale charge transport mechanism. Further, this helps to develop a consistent understanding among a wide range of the physical properties in conducting polymers. In this thesis author has reported the results of experiments at ultra low temperature (mk) and ultra high magnetic field which give more insight about the roles of electron-electron interaction(EEI) and disorderin charge transport properties. This thesis describes a detailed study of charge transport and NMR relaxation in three representative conducting polymers namely polypyrrole(PPy)., poly-3-methylthiophene(P3MT) and poly3-hexylthiophene(P3HT). The emphasis is to understand the charge transport phenomena and NMR relaxation, especially at ultra low temperatures (down to 20 mk) and high magnetic field (up to 23.4 T). The NMR T1 relaxation mechanisms are discussed in terms of (i) Korringa relaxation, (ii) relaxation due to spin diffusion to paramagnetic centers (SDPC) amd (iii) reorientation of symmetric groups, depending upon the temperature range.

Magister Scientiae - MSc (Chemistry) / Pollutants such as polycyclic aromatic hydrocarbons (PAHs) are known for their toxic effects which may lead to the cause of degenerative diseases in both humans and animals. PAHs are widespread in the environment, and may be found in water, food, automotive industry and petrochemical industries to name but a few sources. Literature reports have highlighted industrial workplace exposure to PAHs as a leading cause for development of cancer in workers. Particularly, workers in the petrochemical industry are adversely affected and the incidence of skin and lung cancer in this population group is high. The United States of America in its guidelines developed by environmental protection agency (EPA) has identified 18 PAHs as priority pollutants. Among these are anthracene, benzo[a]pyrene and pyrene which have been selected as the focal point of this study due to their significance in the petrochemical industry. Due to the carcinogenic and mutagenic properties reported in literature for certain PAHs, there have been monitoring procedures taken in most countries around the world. The commonly used analytical methods for the detection of PAHs from industrial samples are high performance liquid chromatography (HPLC) coupled to fluorescence detection, membrane filtration, ozonation and reverse osmosis. Analysis of PAHs from the petrochemical industry is typically performed by HPLC method as well as sono-degredation in the presence of oxygen and hydrogen peroxide.