Presence Of Charge-transfer Complex Research Articles

In Situ Spectrophotometric Investigation of Charge Transfer Complexes Between Triamterene, a Management of Hypertension Drug, and Four Kinds of Nitro Acceptors in Different Organic Solvents

A UV–Vis spectrophotometric method was used to confirm the intermolecular charge-transfer complexes of the drug triamterene (TM) donor with four nitro π-acceptors (2,4,6-trinitrophenol (PA), 4-nitrophenol (4-NP), 4-nitroacetophenone (4-NAP) and m-dinirobenzene (m-DNB)) in methanol, ethanol, acetone, acetonitrile, chloroform, dichloromethane, and dichloroethane at 25 °C. The spectra showed chemical shifts upon the addition of TM to solutions of the nitro acceptors in the solvents. The appearance of new bands or hyper- and hypo-chromic effects confirmed the presence of charge-transfer complexes. The spectra of the complexes of TM and nitro π-acceptors show different absorption bands at different wavelengths for different solvents. The molar ratio method showed a result of 1:1 for the TM–PA system and 1:2 for the TM–4-NP, TM–4NAP, and TM–m-DNB charge-transfer complexes. The physical spectroscopic parameters were calculated, including the formation constant (KCT), molar extinction coefficient (eCT), oscillator strengths (f), ionization potential (Ip), resonance energy (RN), and Gibbs energy (ΔG°). The optical band gap of the TM-nitro charge-transfer complexes was estimated, and there was clearly a relationship between the different kinds of acceptors and their optical band gaps.

Electron transfers in graphitized HZSM-5 zeolites.

In the present work, we report the electron transfers occurring after ionization of the guest molecules of t-stilbene incorporated in graphitized HZSM-5 zeolites and we compare these results with the data obtained previously for graphite-free zeolites. Complementary diffuse reflectance UV-vis and Raman scattering spectroscopies provide evidence for stabilization of long lived charge separated states as observed in non-graphitized ZSM-5. The spectral features indicate that these species are located in the channels of the zeolite structure. However, the pulsed EPR technique shows strong coupling between unpaired electrons and the 13C atoms in the case of graphitized zeolites while this interaction is not observed in normal zeolites. This is assigned to the presence of charge transfer complexes in the close vicinity of graphite areas and to the possible electron transfer to the graphitized domain. Using cyclic voltammetry, an electrochemical response is observed for the first time in such systems demonstrating the role played by graphite in the electron transfers.

Sequence-Controlled Polyurethane Block Copolymer Displays Differentiated Immunoglobulin-G Adsorption That Influences Human Monocyte Adhesion and Activity.

The ability to specify an adsorbed protein layer through the polymer chemistry design of immunomodulatory biomaterials is important when considering a desired immune response, such as reducing pro-inflammatory activity. Limited work has been undertaken to elucidate the role of monomer sequence in this process, when copolymeric systems are involved. In this study, we demonstrate the advantage of an alternating radical copolymerization strategy as opposed to a random statistical copolymerization to order monomers in the synthesis of degradable polar-hydrophobic-ionic polyurethanes (D-PHI), biomaterials originally designed to reduce inflammatory monocyte activation. A monomer system consisting of a vinyl-terminated polyurethane cross-linker, maleic acid (MA), and ethyl vinyl ether (EVE), not only generated a diverse chemical environment of polar, hydrophobic, and ionic functional groups, but also formed a charge transfer complex (CTC) reactive to alternating polymerizations. Conversion of MA and EVE occurred in a constant proportion regardless of monomer availability, a phenomenon not observed in conventional D-PHI formulations. For feeds with unequal molar quantities of MA and EVE, the final conversion was limited and proportional to the limiting reagent, leading to an overall higher polyurethane cross-linker content. The presence of a reactive CTC was also found to limit the monomer conversion. Compared to a D-PHI with random monomer arrangement using methacrylic acid (MAA) and methyl methacrylate (MMA), a reduction in Fab region exposure from adsorbed immunoglobulin G and a reduction in average adherent monocyte activity were found in the sequence-controlled version. These results represent the first example of using an alternating copolymerization approach to generate regularly defined polymer chemistries in radical chain-growth biomaterials for achieving immunomodulation, and highlight the importance of considering sequence control as a design strategy for future immunomodulatory biomaterial development.

Synthesis, single-crystal, DNA interaction, spectrophotometric and spectroscopic characterization of the hydrogen-bonded charge transfer complex of 2-aminopyrimidine with π-acceptor chloranilic acid at different temperature in acetonitrile

The charge transfer (CT) interaction of 2-aminopyrimidine (AP) with chloranilic acid (CLA) as π-acceptor was investigated spectrophotometrically in acetonitrile at different temperatures in the range of 25–50°C. The 1:1 stoichiometry of the synthesized CT complex was detected using straight line method. Benesi–Hildebrand equation was used to determine the association constant (KCT), molar extinction coefficient (ε) and other physical parameters. Various thermodynamics parameters such as enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) were determined using UV–Visible spectrophotometry in acetonitrile at different temperatures. 1H NMR, FTIR, ESI-MS, elemental analyses, and UV–Visible techniques were used to characterize the hydrogen-bonded CT complex. 1H NMR spectroscopy was also used for the analysis of the CT complex where both hydrogen bond and charge transfer were present in its molecular composition. The interaction of the selected organic compound with Ct-DNA was well investigated using fluorescence spectroscopic method. Stern–Volmer constant (Ksv) was used to estimate the fluorescence quenching efficiency. Circular dichroism (CD) spectroscopy was employed to measure the conformational change of DNA in the presence of CT complex. Furthermore, the drug CT complex detected changes in its viscosity. The charge transfer complex was formed as a result of the transfer of the lone pair of electrons from donor to the acceptor and exhibits well resolved charge transfer bands in the regions where absorption by both donor and acceptor were absent. The thermal composition and stability of the CT complex were analyzed using thermogravimetric and differential thermal analysis (TGA and DTA) studies. The X-ray crystal structure was used for the interpretation of the structure of the [(AP)+ (CLA)−] CT complex. The crystal structure indicated that cation and anion are linked through strong N+H----O− type of hydrogen bond.

Effect of iodine doping on the electrical transport mechanism in plasma polymerized 2,6-diethylaniline thin films

The current density–voltage characteristics of pure and iodine doped plasma polymerized 2,6-diethylaniline (PPDEA) thin films of different thicknesses ranging from 150 to 450nm with aluminum (Al)/PPDEA/Al structure have been investigated at room temperature. The direct current electrical conductivity has showed a higher value due to iodine doping of PPDEA thin film. In contrast to pure PPDEA thin films where the most probable conduction mechanism is electrode limited Schottky type, Poole–Frenkel (PF) conduction mechanism is found to be operative in iodine doped PPDEA thin films. The PF conduction mechanism in iodine doped PPDEA thin films may have generated due to the charge transfer complex formation through donor type monomer and acceptor type iodine. The presence of charge transfer complex is confirmed by a new absorption shoulder/peak in ultraviolet–visible spectrum of iodine doped PPDEA thin film.

Charge Flow Mechanism and Charge Effects in Polymer Film Structures

The mechanisms of charge flow in organic polymer PEPC and 3,6-di-Br-PEPC films, V2O5 xerogel and composite films of PEPC + N mas.% V2O5 and 3,6-di-Br-PEPC + N mas.% V2O5 are investigated. The conductivity of composite films is established to depend on the polymer nature, V2O5 content, and presence of charge-transfer complexes between the polymers and vanadium oxides. In PEPC + N mas.% V2O5 films the volume charge and the trap field effect play an important role as distinct from the case of bromated polymer composites.