Dye Modified Phenylenediamine Oligomers: Theoretical Studies on Drug Binding for Their Potential Application in Drug Sensors

The present work reports, for the first time, synthesis of dye incorporated o-phenylenediamine (OBB) with a view to obtain a conjugated oligomer with enhanced functionality. The structure was confirmed by IR studies, while the electronic transitions were confirmed by UV visible studies. The dye modified oligomer showed one order higher fluorescence intensity than the pristine Bismarck Brown (BB) dye. Confocal imaging showed red emission which could be utilized in near infra-red imaging. Density functional theory (DFT) studies were carried out to predict the theoretical properties of the oligomers. The energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital orbital were computed to explore how the HOMO energies of the reactants initiated the electronic interactions between them. The interaction energies were correlated to conjugation/hyper conjugation stabilization energies of the natural bond orbitals (NBO) via the DFT method using the B3LYP functional with the 6-311G(d) basis set on Gaussian 09 software. Drug binding was evaluated through simulation of interaction energy, (ΔEA-x) with drugs such as captopril, propranolol, thiazide, and fentanyl. The results predicted that the oligomer could be developed into a fentanyl drug sensor.

Optical and computational study of the trans ↔ cis reversible isomerization of the commercial bis-azo dye Bismarck Brown Y

The trans-cis-trans isomerization behaviour of Bismarck Brown Y (BBY) during and after irradiation with visible light, was characterized in detail for the first time by means of optical pump-probe experiments, to study the geometric inter-conversion of bis-azobenzene both in solution and embedded in multi-layered polymeric thin films. The rate constants observed for the thermal cis-trans back isomerization permit a determination of how the thermal isomerization is influenced by its local environment. In both solution and when incorporated into multi-layered thin films, the thermal relaxation observed for the commercial azo dye BBY showed a highly unusual biexponential decay, which clearly demonstrates two distinct isomerization processes. The cis decay showed an anomalous fast isomerization process on the timescale of milliseconds, followed by a slower isomerization process with a cis lifetime on the order of seconds. It was further observed that the faster isomerization process was influenced more by its local environment than was the slower process. The faster isomerization process also displayed a higher rate constant in aprotic solvents such as THF and DMF compared to that observed in protic solvents such as ethanol and water. Additionally, a higher rate constant was observed in solution compared to the multi-layered thin films where motion of the azo molecules was likely more restricted. Following recrystallization of the BBY azo dye, the more expected monoexponential decay was observed for the cis isomer in solution, with a single cis lifetime calculated on the timescale of seconds. This timescale corresponded well to values predicted by density functional theory calculations.

Mechanism of Nanocomposite Formation in the Layer-by-Layer Single-Step Electropolymerization of π-Conjugated Azopolymers and Reduced Graphene Oxide: An Electrochemical Impedance Spectroscopy Study

This work presents a study of the formation mechanism of electrochemically deposited alternating layers of azopolymer and graphene oxide, as well as a systematic study of the physicochemical characteristics of the resulting nanocomposite films by electrochemical impedance spectroscopy. The nanocomposite films were constructed by cyclic electropolymerization, which allowed for the assembly of thin films with alternating azopolymers and reduced graphene oxide (rGO) layers in one step. Morphological characterizations were performed by atomic force microscopy and scanning electron microscopy and verified that the electrodeposition of the poly(azo-BBY) polymeric film occurred during the anodic sweep, and the deposition of graphene oxide sheets took place during the cathodic sweep. By analyzing the electrochemical impedance spectra using equivalent circuit models, variations in the resistance and capacitance values of the system were monitored as a function of the amount of electrodeposited material on the fluorine doped tin oxide electrode. In addition, the interfacial phenomena that occurred during the electroreduction of the rGO sheets were monitored with the same method.

A Chemiresistor Sensor Based on Azo-Polymer and Graphene for Real-Time Monitoring of Mitochondrial Oxygen Consumption

In the present study, a chemiresistor sensor based on a poly(Bismarck Brown Y)-reduced graphene oxide nanocomposite was developed to analyze the respiratory capacity of the constituent complexes of the electron transport chain. The sensorial platform was characterized using electrochemical impedance spectroscopy, and oxygen detection was accomplished by measuring the resistive properties of the sensor at fixed AC frequency. The impedance decreased significantly in response to small variations of the O₂ concentrations tested up to saturation of the electrolyte solution with molecular oxygen. The resistive response of the sensor at 0.1 Hz was linear over the oxygen concentration range from 1.17 × 10^-5 mol L^-1 to 1.02 × 10^-3 mol L^-1, with a detection limit of 3.60 × 10^-7 mol L^-1. Using the new O₂ sensing platform, we monitored gradients in static cultures of adherent cells exposed to graded oxygen both at rest and upon metabolic stimulation. Under high dissolved oxygen conditions, the respiration of resting cells dictated that local O₂ was moderately reduced, while cell metabolic stimulation triggered a major redistribution of O₂. The usefulness of the developed sensor was demonstrated by continuous monitoring of mitochondrial oxygen consumption in various biologic applications.