Open Circuit Potential Amperometry Research Articles

Well designed iridium-phosphinite complexes: Biological assays, electrochemical behavior and density functional theory calculations

Mononuclear phosphinite Iridium complexes based on ferrocene group have been prepared and characterized by various spectroscopic techniques. The complexes were subjected to cyclic voltammetry studies in order to determine the energies of HOMO and LUMO levels and to estimate their electrochemical and some electronic properties. Organic complex-based memory substrates were immobilized using TiO2-modified ITO electrodes, and the memory functions of phosphinite-based organic complexes were verified by chronoamperometry (CA) and open-circuit potential amperometry (OCPA). Extensive theoretical and experimental investigations were directed to gain a more profound understanding of the chemical descriptors and the diverse electronic transitions taking place within the iridium complexes, as well as their electrochemical characteristics. The quantum chemical calculations were carried out for the iridium complexes at the DFT/CAM-B3LYP level of theory in the gas phase. Furthermore, the antioxidant, antimicrobial, DNA binding, and DNA cleavage activities of the complexes were tested. Complex 2 exhibited the highest radical scavenging activity (67.5 ± 2.24 %) at 200.0 mg/L concentration. It was observed that the complexes formed an inhibition zone in the range of 8–15 mm against Gram + bacteria and in the range of 0–13 mm against Gram – bacteria. The agarose gel electrophoresis method was used to determine the DNA binding and DNA cleavage activities of the complexes. All of the tested complexes had DNA binding activity; however, complexes 1, 2, and 8 showed better binding activity than the others.

Biological assays, electrochemical behavior, and theoretical DFT calculations of Ru(II) complexes of chiral phosphinite based based on β-amino alcohols: Transfer hyrogenation of ketones using a HCOOH/Et3N mixture

Synthesis of two phosphinite ligands based on β-amino alcohols, in high yields has been demonstrated. When we treated [Ru(arene)(μ-Cl)Cl]2 {arene:p-cymene,benzene} with chelating phosphinite ligands, we obtained neutral Ru(II)-complexes possessing the general formula [Ru(arene)phosphiniteCl2]. The structure of the ligands and complexes was confirmed using analytical and spectroscopic techniques. The quantum chemical calculations were carried out for the ruthenium complexes at the DFT/CAM-B3LYP level of theory in gas phase. The phosphinite complexes were subjected to cyclic voltammetry studies in order to determine the energies of HOMO and LUMO levels and to estimate their electrochemical and some electronic properties. Organic complex-based memory substrates were immobilized using TiO2-modified ITO electrodes, and the memory functions of phosphinite-based organic complexes were verified by chronoamperometry (CA) and open-circuit potential amperometry (OCPA). In the present study, the antioxidant potentials of ruthenium-based p-cymene and benzene complexes through DPPH radical scavenging, metal chelating, and reducing power activities were also determined. In addition, DNA binding abilities and antimicrobial activities of these complexes against pathogenic bacteria were studied. Finally, the ruthenium complex, (2S)-1-{[(2S)-2-[(diphenylphosphanyl)oxy]propyl][(1R)-1-phenylethyl]amino}propan-2-yldiphenyl phosphinitobis[dichloro(η6-benzene)ruthenium(II)] also catalyzed asymmetric transfer hydrogenation of acetophenone with high conversion (up to 99%) and good enantioselectivity (ee up to 89 %), in the existence of formic acid and triethylamine in dichloromethane medium under air atmosphere.

Ferritin based bionanocages as novel biomemory device concept

Ferritin is an iron cage having protein, capable of extracting metal ions in their cages and a consequence of the electron transfer of metal ions in their cage by reduction and oxidation processes, electrochemical information storage devices can be designed. In this work, ferritin based protein biomemory substrate has been synthesized by using Amino Acid (monomer) Decorated and Light Underpinning Conjugation Approach (ANADOLUCA) method, which utilizes photosensitive electron transfer based microemulsion co-polymerization as nanobead form of ferritin. Protein substrate contains metal ions such as silver and copper or metal ion pairs namely, silver-copper (Janus bionanocage) and co-polymeric shell of the photosensitive crosslinker protein. The redox behavior of bionanocages differentiates electrochemical "writing" and "erase" states depending on these metal ions (silver or copper) or metal ion pairs. The bionanocages based biomemory substrates have been immobilized using graphene modified glassy carbon electrodes and the memory functions of ferritin based bionanocages have been confirmed by chronoamperometry (CA) and open circuit potential amperometry (OCPA). The stability and durability of multi-state memory devices represent promising properties for future bioelectronic information technologies.

Nano-hemoglobin film based sextet state biomemory device by cross-linked photosensitive hapten monomer

In this study, a biomemory device, consisting of hemoglobin (Hb) cross-linked by MACys-Ru(bipyr)2-MACys) photosensitive monomer cross-linkers, which have memory effect through both Ru3+/2+ in hapten monomer and Fe3+/2+ in redox active center of Hb through multi-charge transfer mechanism, has been improved. Cyclic voltammetry (CV) has been used to determine the redox property of the Hb cross-linked MACys-Ru(bipyr)2-MACys) hapten. Three memory functions, writing, reading and erasing of the fabricated biomemory device, have been accomplished by chronoamperometry (CA) and open-circuit potential amperometry (OCPA). The reliability and repeatability of the biodevice consisting of the p(Hb-co-MACys-Ru(bipyr)2-MACys) sextet state bio-memory layer have been analysed. The Hb film based biodevice on gold electrodes has shown ≥ 2 months the retention time and switched until 106 times continuous cycling without degradation in efficiency. Other hand, the topography of p(Hb-co-MACys-Ru(bipyr)2-MACys) layer on the gold surface has investigated by scanning electron microscopy (SEM) and EDX data.

Multistate proteinous biomemory device based on redox controllable hapten cross-linker

A multistate biomemory device consisting of cytochrome c (Cyt-c) photosensitively cross-linked by MACys-Ru(bipyr)2-MACys hapten molecules, which have memory effect through a charge transfer mechanism, has been developed. In this study, it has suggested a highly resolute surface-confined switch composed a signal-enhanced electro-active protein (Cyt-c) co-polymerized on the gold substrates that can be controlled by redox property through Ruthenium based cysteine monomer hapten, MACys-Ru(bipyr)2-MACys as an ANADOLUCA photosensitive cross-linker. The photosensitive cross-linking of the Cyt-c protein on the gold surface topography has been determined by the scanning electron microscopy (SEM). Two state memory functions, writing and erasing of the developed biomemory device, have been investigated by the chronoamperometry (CA) and open-circuit potential amperometry (OCPA). The polymeric proteinous memory device, p(MACys-Ru(bipyr)2-MACys-co-Cyt-c) layer, on the gold electrode is stable and repeatable up to with 104 times continuous cycle.

An Advanced Experiment for Studying Electron Transfer and Charge Storage on Surfaces Modified with Metallic Complexes

Data-storage devices can be fabricated by modifying different surfaces with metallic complexes. The required time to write information and the time that information remains is crucial for the performance of the electronic device. We illustrate this technological application of molecules by adsorbing a polyoxometalate on graphite and characterization by ac voltammetry and open circuit potential amperometry. A charge-transfer constant from the surface to the electrode of 118 s–1 and a charge-storage half-life of 42 s were calculated by these methodologies. This laboratory can be easily performed and adapted in any advanced electrochemistry or materials science laboratory.

Multi-Functional Biomemory Device Composed of Recombinant Metalloprotein

We developed a multi-functional biomemory device composed of cytochrome c and recombinant azurins which have different metal ions in the core. Azurin, one of the well-known metalloproteins, was modified by attaching cysteine residue containing thiol functional group for direct immobilization without chemical linkers. The immobilization of metalloproteins was confirmed by atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectroscopy. The redox properties of immobilized recombinant azurin were validated with cyclic voltammetry (CV), and memory functions using various metalloprotein structures were confirmed by the technique of open circuit potential amperometry (OCPA). We achieved various practical functions based on basic memory functions including write, erase, and read using recombinant azurin and other metalloproteins, and this proposed multifunctional biodevice could be directly applied to the realization of bioelectronics device for next generation, such as single molecular functional device, bioprocessor and biocomputing system.

Multifunctional 4-bit biomemory chip consisting of recombinant azurin variants

We developed a multi-functional 4-bit biomemory chip that consisted of recombinant azurin variants. The azurin was modified to introduce cysteine-residues. In addition, the Cu ion in this recombinant azurin protein was substituted with various other metal ions such as Co, Mn, Fe and Ni ion to allow the protein to perform various memory functions. Each metal-substituted recombinant protein was directly self-assembled attached onto Au surface via the thiol group of the cysteine. UV–VIS spectroscopy was performed to confirm the metal substitution. Atomic force microscopy was used to measure the film organization. Also, the 4 different azurin variants were investigated to assess the electrochemical behavior. Cyclic voltammetry and an open circuit potential indicated that the azurin variants had different redox peaks and specific open circuit potential values. Using these parameters, memory function was verified by chronoamperometry and open circuit potential amperometry. Therefore, a multi-bit biomemory chip was successfully developed. The results presented here provide a new approach, concept and material combination for the development of biomemory systems using recombinant protein. If a low electrochemical signal from a few single proteins could be achieved, it may be possible to substitute silicon-based memory devices with biological-based memory devices.

Multifunctional DNA-based biomemory device consisting of ssDNA/Cu heterolayers

In the present study, we developed a novel DNA-based biomemory device that was comprised of ssDNA/Cu heterolayers on Au electrodes. As a conducting material, a thiol-modified single strand DNA (26 bp) was designed and immobilized on the Au electrode without the need for any linker material. Cu 2+ ions, which acted as the active site, were then chemically absorbed on the external structure of ssDNA through electrostatic interactions. The presence of the fabricated ssDNA/Cu heterolayer was confirmed by surface plasmon resonance (SPR) spectroscopy and Raman spectroscopy. Cyclic voltammetry experiments were carried out to investigate the redox properties of ssDNA/Cu hybrids to obtain the oxidation and reduction potential. Based on measured oxidation and reduction potential, a ROM-type, 3-state type, and WORM type DNA memory functions were demonstrated by chronoamperometry (CA) and open circuit potential amperometry (OCPA). This proposed device acts and operates the memory function very well. In the near future, DNA based biomemory device in this study could provide the alternative to the inorganic electronic device when molecular scaled immobilization control and signal measurement are achieved.

Ferredoxin Molecular Thin Film with Intrinsic Switching Mechanism for Biomemory Application

A biomemory device consisting of cysteine modified ferredoxin molecules which possess a memory effect via a charge transfer mechanism was developed. For achieving an efficient bioelectronic device, cysteine modified ferredoxin was developed by embodying cysteine residues in ferredoxin by site--directed mutagenesis method to directly coordinate with the gold (Au) surface without use of any additional linkers. The thin film formation of ferredoxin molecules on Au electrode is confirmed by surface plasmon resonance (SPR) spectroscopy and scanning tunneling microscope (STM). Cyclic voltammetry (CV) and open circuit potential amperometry (OCPA) methods were used to verify the memory switching characteristics of the fabricated device. The charge transfer between ferredoxin protein molecules and Au electrode enables a bi-stable electrical conductivity allowing the system to be used as a digital memory device. Data storage is achieved by applying redox voltages which are within the range of -500 mV. These results suggest that the proposed device has a function of memory and can be used for the construction of a nano-scale bioelectronic device.

Nanoscale protein-based memory device composed of recombinant azurin

In this present study, a nanoscale protein-based memory device consisting of recombinant azurin with its cysteine residues modified by site-directed mutagenesis method has been developed. Cysteine residues were modified to directly coordinate with the gold surface without use of any chemical linkers. Cyclic voltammetry (CV) method was used to measure the redox behavior of the immobilized azurin. Open-circuit potential amperometry (OCPA) technique allowed observing the memory characteristics including “write”, “erase” and “read” functions of a nanoscale memory device. The variations in topology and the electron transfer properties, under the application of redox potentials, of the azurin adsorbed on Au was accomplished with electrochemical scanning tunneling microscopy. Data storage is achieved by applying redox potentials which are within the range of 500 mV. Finally the reliability of the proposed device has been examined. The key performance of the present system is it enables the memory working mechanism at nanoscale without degradation in performance and hence can be used as a nanoscale information storage device.

Nanoscale film formation of ferritin and its application to biomemory device

A redox protein, ferritin is used as a functional constituent of the developed biomemory device. The concept of molecular device mainly depends on the solidification of biomolecules of interest and on the realization of properties of molecule immobilized on a selected substrate. Here, we immobilized the biomolecule, ferritin protein on gold substrate using an organic linker 11-mercaptoundecanoic acid (11-MUA). The immobilization of the protein on the gold substrate was confirmed by surface plasmon spectroscopy, Raman spectroscopy, and atomic force microscopy (AFM). The basic two memory functions, reading and writing of the developed biomemory device, were investigated by open-circuit potential amperometry (OCPA) using the redox property of the biomolecule of interest. The surface topography investigation by scanning tunneling microscopy (STM) shows that the robustness of the ferritin-based biomemory device was validated by the repeated electrochemical performance. These results show the developed biomemory device as a step towards the protein-based nanobiochip.

Multi-bit biomemory consisting of recombinant protein variants, azurin

In this study a protein-based multi-bit biomemory device consisting of recombinant azurin with its cysteine residue modified by site-directed mutagenesis method has been developed. The recombinant azurin was directly immobilized on four different gold (Au) electrodes patterned on a single silicon substrate. Using cyclic voltammetry (CV), chronoamperometry (CA) and open circuit potential amperometry (OCPA) methods the memory function of the fabricated biodevice was validated. The charge transfer occurs between protein molecules and Au electrode enables a bi-stable electrical conductivity allowing the system to be used as a digital memory device. Data storage is achieved by applying redox potentials which are within the range of 200 mV. Oxidation and open circuit potentials with current sensing were used for writing and reading operations respectively. Applying oxidation potentials in different combinations to each Au electrodes, multi-bit information was stored in to the azurin molecules. Finally, the switching robustness and reliability of the proposed device has been examined. The results suggest that the proposed device has a function of memory and can be used for the construction of nano-scale multi-bit information storage device.

Characterization of Charge Storage in Redox-Active Self-Assembled Monolayers

Self-assembled monolayers (SAMs) of thiol-derivatized alkyl ferrocenes and Zn tetraarylporphyrins on a gold surface have been characterized under open circuit conditions using fluorescence imaging microscopy and a varietyof electrochemical methods. The fluorescence of the neutral form of the Zn tetraarylporphyrin SAM and the electrode cell potential are monitored simultaneously after oxidation of the SAM and subsequent establishment of an open circuit condition. These experiments capitalize on the fact that the neutral Zn tetraarylporphyrin SAM is fluorescent whereas emission from the oxidized Zn tetraarylporphyrin SAM is quenched. Accordingly, the fluorescence recovery after disconnection from an oxidizing potential provides an independent measure of the change in oxidation state of the porphyrin SAM as a function of time after the cell is open-circuited. This measurement demonstrates that the porphyrin SAM remains oxidized for an extended period (hundreds of seconds) even though the electrochemical cell potential decays rapidly to the open circuit potential (OCP). Cyclic voltammetry was used to confirm the electrochemical properties of the redox SAMs and to determine the surface coverage of the redox-active molecules. A new method, designated open circuit potential amperometry, was used to read the charge of the oxidized SAM at the OCP after charging currents have decayed away. Additionally, open circuit potential voltammetry yields a sigmoidal response with a characteristic half-wave potential identical to that observed with cyclic voltammetry, indicative of a Nernstian process. Collectively, these studies show that the electrochemical cell discharges to the OCP quickly, that the SAM remains oxidized under these conditions, and that these methods can be used to quantitatively determine the amount of stored charge in the SAM.