Search results for "Spectroscopy"
showing 10 items of 10293 documents
Metal-organic frameworks conjugated with biomolecules as efficient platforms for development of biosensors
2021
Abstract Recent developments in the field of metal-organic frameworks (MOFs) have renewed the interests of scientists to bring about a major breakthrough in this field soon. These particles consist of ultra-highly porous and tremendous internal surface areas with extraordinary variabilities that make them highly potent compounds in nanomedicine. Moreover, low weight, large free volumes, and multiple functionalities of these particles have made them extremely attractive for various applications. Along with a critical role in the adsorption and separation of different analytes, they also have an immense role in the development of biosensor platforms that are expected to pave the way for accur…
Aptamer-based assay of biomolecules: Recent advances in electro-analytical approach
2017
Electrochemical aptasensors, which are based on the specificity of aptamer-target recognition, with electrochemical transduction for analytical purposes have received particular attention due to their high sensitivity and selectivity, simple instrumentation, as well as low production cost. This review summarizes advances from 2009 to January 2017 in the development of electrochemical aptasensors for biological molecules, including small molecules, nucleic acids, and proteins. Various aptasensing strategies are assessed according to their potential for reaching relevant limits of sensitivity, specificity, and degrees of multiplexing. Furthermore, we address the remaining challenges and oppor…
Nonlinear optical susceptibilities of polysilanes: exciton effect
1992
Abstract Third-order nonlinear optical susceptibilities of σ-conjugated one-dimensional polymers have been calculated in a tight-binding model by taking account of the formation of excitons due to long-range Coulomb interactions. The spectrum of third-harmonic generation (THG) exhibits peaks due to excitons as well as unbound electron—hole states, in contrast to the linear absorption spectrum which is dominated by the lowest exciton state. The results are in excellent agreement with recent experiments in polysilanes not only for THG but also for linear absorption, two-photon absorption, and electroabsorption in a mutually consistent way.
Cooperative High-Temperature Spin Crossover Accompanied by a Highly Anisotropic Structural Distortion
2016
Spin transitions are a spectacular example of molecular switching that can provoke extreme electronic and structural reorganizations in coordination compounds. A new 3D cyanoheterometallic framework, [Fe(pz)(Au(CN)2)2], has been synthesized in which a highly cooperative spin crossover has been observed at 367 and 349 K in heating and cooling modes, respectively. Mössbauer spectroscopy revealed a complete transition between the diamagnetic and paramagnetic states of the iron centres. The low-spin-to-high-spin transition induced a drastic structural distortion involving a large one-directional expansion (ca. 10.6%) and contraction (ca. 9.6%) of the lattice. Negative thermal expansion along th…
Characterization of poly(N-alkylanilines) by Raman spectroscopy
2007
Abstract Thin films of poly( N -alkylaniline) were synthesized in acidic aqueous solution and in mixtures of aqueous and organic solvents. The polymer films (alkyl = methyl, ethyl, propyl and butyl) were characterized by Raman spectroscopy with the excitation wavelengths of 514.5, 632.8 and 780 nm. The main Raman bands have been characterized for the leucoemeraldine, emeraldine and pernigraniline oxidation states between −0.2 and 0.8 V (vs. Ag|AgCl). This fundamental study shows that the structure of the half-oxidized emeraldine form contains quinoid units, which supports the commonly accepted oxidation and reduction scheme of poly( N -alkylanilines).
Synthesis of new electroactive polymers by ion-exchange replacement of Mg(II) by 2H+ or Zn(II) cations inside Mg(II) polyporphine film, with their su…
2014
Abstract It has been demonstrated that the treatment of the magnesium polyporphine of type I, pMgP-I, by trifluoroacetic acid in acetonitrile may be used to replace initial central Mg(II) cations inside the monomeric macrocycle units by protons, to get a new electroactive polymer, “free-base polyporphine of type I”, pH2P-I. In its turn, these inserted protons may be replaced by Zn(II) cations via the film treatment with zinc acetate in organic solvent, to get another new electroactive polymer, “zinc polyporphine of type I”, pZnP-I. These changes of central ions inside monomer units manifest themselves by characteristic modifications of their electroactive properties as well as of UV–visible…
Electropolymerization of N-methylanthranilic acid and spectroelectrochemical characterization of the formed film
2009
Abstract The electropolymerization of N-methylanthranilic acid (NMAA) is reported in this paper. The monomer is substituted both at ortho- and N-position and, to the best of our knowledge, it has not been previously electropolymerized. Electropolymerization of NMAA was done on glassy carbon and optically transparent (indium) tin oxide electrodes. The obtained films, which are probably of an oligomeric nature (oligoNMMA), were characterized with cyclic voltammetry (CV), in situ UV–vis and Raman spectroscopy, ex situ FTIR spectroscopy and scanning electron microscopy (SEM). Our results show that NMAA can be electropolymerized as thin films in 1.0 M HClO4, but the oxidation and reduction peak …
Multilayer Thin Films by Layer-by-Layer Assembly of Hole- and Electron-Transport Polyelectrolytes: Optical and Electrochemical Properties
2006
In this paper, we pressent the synthesis of a series of p-type and n-type semicondnctring polyelectrolytes with triarylamine, oxadiazole, thiarliazole and triazine moictes. The synthesized polymeric hole and electrom iransport materials were examined optically and electrochemically using UV/Vis spectroscopy. PL spectroscopy and CV. Based on the optical and electrochemical data, each of the energy levels were calculated and all values suggested that the were promising hole-(p-type) or alectron=transprot (n-type) materials for devices. Moreover, the synthesized ionie polymers were suitable for LBL thin film deposition from ditute polymer solutions and the multilayers were fully characterized …
In-situ polymerization of polyaniline in radiation functionalized polypropylene films
2015
Abstract In-situ generation of a nanodispersed conductive polymer within a polypropylene matrix has been pursued in order to obtain flexible, conductive films. Radiation grafting of acrylic acid to polypropylene (PP) has been applied to insert carboxyl functionalities on PP. The radiation-grafted films have been further derivatized with a variety of diamines and used as substrates for in-situ chemical oxidative polymerization of polyaniline (PANI). PANI grows as a thin skin from the surface of the film as well as an interpenetrated network in its interiors. Evidence of chemical attachment of PANI to PP has been sought by performing FTIR and XPS analyses after extraction of the unbound polym…
Electrical properties of γ-crosslinked hydrogels incorporating organic conducting polymers
2007
Abstract Hydrogel composites containing nanoparticles of the protonated emeraldine form of polyaniline (PANI-PE) have been synthesised by γ-irradiation, using either polyvinyl pyrrolidone (PVP) or polyvinyl alcohol (PVA) as steric stabilisers. Swelling behaviour of both hydrogels is reported, together with an electrical characterisation of composites, before and after gel network formation, performed by cyclic voltammetry and impedance spectroscopy. Similarities and differences between the two composite systems are discussed.