Charge Transfer Techniques Research Articles

The correlation of electrochemical measurements and molecular junction conductance simulations in β-strand peptides.

Understanding the electronic properties of single peptides is not only of fundamental importance, but it is also paramount to the realization of peptide-based molecular electronic components. Electrochemical and theoretical studies are reported on two β-strand-based peptides, one with its backbone constrained with a triazole-containing tether introduced by Huisgen cycloaddition (peptide 1) and the other a direct linear analogue (peptide 2). Density functional theory (DFT) and non-equilibrium Green's function were used to investigate conductance in molecular junctions containing peptides 3 and 4 (analogues of 1 and 2). Although the peptides share a common β-strand conformation, they display vastly different electronic transport properties due to the presence (or absence) of the side-bridge constraint and the associated effect on backbone rigidity. These studies reveal that the electron transfer rate constants of 1 and 2, and the conductance calculated for 3 and 4, differ by approximately one order of magnitude, thus providing two distinctly different conductance states and what is essentially a molecular switch. A definitive correlation of electrochemical measurements and molecular junction conductance simulations is demonstrated using two different charge transfer techniques. This study furthers our understanding of the electronic properties of peptides at the molecular level, which provides an opportunity to fine-tune their molecular orbital energies through suitable structural manipulation.

Orbital Signatures as a Descriptor of Regioselectivity and Chemical Reactivity: The Role of the Frontier Orbitals on 1,3-Dipolar Cycloadditions

The FERMO concept emerges as a powerful and innovative implement to investigate the role of molecular orbitals applied to the description of breakage and formation of chemical bonds. In this work, Hartree-Fock (HF) theory and density functional (DFT) calculations were performed for a series of four reactions of 1,3-dipolar cycloadditions and were analyzed by molecular orbital (MO) energies, charge transfer, and molecular dynamics (ADMP) techniques for direct dynamics using the DFT method. The regioselectivity for a series of four 1,3-dipolar cycloaddition reactions was studied here using global and local reactivity indexes. We observed that the HOMO energies are insufficient to describe the behavior of these reactions when there is the presence of heteroatoms. By using the frontier effective-for-reaction molecular orbital (FERMO) concept, the reactions that are driven by HOMO, and those that are not, can be better explained, independent of the calculation method used, because both HF and Kohn-Sham methodologies lead to the same FERMO.

Fabrication of a highly sensitive penicillin sensor based on charge transfer techniques

A highly sensitive penicillin biosensor based on a charge-transfer technique (CTTPS) has been fabricated and demonstrated in this paper. CTTPS comprised a charge accumulation technique for penicilloic acid and H+ ions perception system. With the proposed CTTPS, it is possible to amplify the sensing signals without external amplifier by using the charge accumulation cycles. The fabricated CTTPS exhibits excellent performance for penicillin detection and exhibit a high-sensitivity (47.852mV/mM), high signal-to-noise ratio (SNR), large span (1445mV), wide linear range (0–25mM), fast response time (<3s), and very good reproducibility. A very lower detection limit of about 0.01mM was observed from the proposed sensor. Under optimum conditions, the proposed CTTPS outstripped the performance of the widely used ISFET penicillin sensor and exhibited almost eight times greater sensitivity as compared to ISFET (6.56mV/mM). The sensor system is implemented for the measurement of the penicillin concentration in penicillin fermentation broth.

An enhanced glucose biosensor using charge transfer techniques

An enhanced glucose biosensor based on a charge transfer technique glucose sensor (CTTGS) is described and demonstrated experimentally. In the proposed CTTGS, which is accumulation method ( d-gluconate + H +) ion perception system, the quality of output signal with “signal integration cycles” is high. With the proposed CTTGS it is possible to amplify the sensing signals without an external amplifier by using an accumulation cycle. It can be supposed that measurements of small ( d-gluconate + H +) ion fluctuation are difficult by ion-sensitive field effect transistor (ISFET) because the theoretical maximum sensitivity is only 59 mV/pH and the small output signals are buried in the 1/ f noise component of the metal–insulator–semi-conductor field-effect transistor (MISFET). Therefore, the CTTGS has many advantages, such as high sensitivity, high accuracy, high signal-to-noise ratio (SNR), and has been successfully demonstrated using a charge transfer technique. The CTTGS exhibited excellent performance for glucose with a large span (1445 mV) and good reproducibility. Moreover, the CTTGS has good sensitivity in this range of 7.22 mV/mM, a lower detection limit of about 0.01 mM/L and an upper detection limit of about 200 mM/L compared with amperometric glucose analysis which has been studied recently. Under optimum conditions, the proposed CTTGS exceeds the performance of the widely used ISFET glucose sensor. The sensitivity of the CTTGS (7.22 mV/mM) was seven times higher than that of the ISFET (1 mV/mM). Furthermore, the sensitivity obtained for human glucose levels was 29.06 mV/mM with a non-linear error of ±0.27%; the linearity is y = 0.0294 x + 1.8612 and R 2 = 0.9999, which is acceptable for clinical application. Real sample analysis is investigated in blood glucose level by our developed CTTGS ISFET system.

Highly sensitive ion sensors using charge transfer technique

Accumulation method ion sensor (AMIS), an expected high sensitive ion sensor, is proposed and prototype one is fabricated using a charge coupled device (CCD) process. The principle of the accumulation method ion sensor is based on the charge transfer techniques. The AMIS is operated in a signal integration mode. Charges corresponded to an ion concentration is transferred from a sensing part to the floating diffusion region on several times, and the signal charges are accumulated in the floating diffusion region. It is expected that the signal-to-noise ratio (SNR) of the chemical potential information increases n 0.5 times, as the signal is integrated n times. The output signal was measured by using the equivalent signal. It was found that the output signal from AMPS, which was integrated five times, was lineally changed to the input signal and the total sensitivity was 450 mV/pH. This sensitivity is about nine times higher than that of ion sensitive field-effect transistor (ISFET).

Colorimetric and Fluorimetric Methods for the Determination of Some Antihistaminics Using Acid Dyes and Charge Transfer Techniques

The acid dyes eosin B and tropeolin oo were used for the determination of terfinadine, astemizole and acrivastine in the presence of Mcllvain buffer of a suitable pH. The formed ion-pairs were extracted with chloroform and the absorbances were measured at 530–535 nm and 410 nm in the case of eosin B and tropeolin oo, respectively. In addition terfinadine, astemizole and acrivastine were determined fluorimetrically using eosin B. The fluorescence intensity was measured at 480 nm excitation and 555 nm emission. Conformity with Beer's law was evident over a concentration range of 2–20 μg/ml in the colorimetric methods and of 0.16 – 0.96 μg/ml in the fluorimetric methods. The charge transfer technique was also applied for the determination of astemizole and acrivastine using iodine and 2,3 dichloro, 5, 6 – dicyano – p-benzoquinone (DDQ). Absorbances were measured at 286 nm and 292 nm, respectively, in the iodine method, and at 461 nm in the DDQ method. Conformity with Beer's law was evident over concentration range of 1 – 12 μg/ml and 20 – 200 μg/ml in iodine and DDQ methods respectively. The precision of the proposed methods was tested by applying them for the determination of pure samples of terfinadine, astemizole and acrivastine. The mean percentage recovery of terfinadine, astemizole and acrivastine lies in the range 99.49-100.72% in eosin B method, 99.79-100.16% in tropeolin oo method, 100.01-101.00% in the fluorimetric method. In the charge transfer methods the mean percentage recovery of astemizole and acrivastine lies in the range 99.61-100.40% and 100.02-100.30% in iodine and DDQ methods respectively. The proposed methods were successfully applied for the determination of the drugs in their pharmaceutical dosage forms and their validities were ascertained by applying the standard addition technique.

Electronic conductivity of AgI using d.c. polarization and charge transfer techniques

ESR spectra have been determined for nine binuclear, exchange-coupled complexes of vanadyl(IV) with tartrate(4−), monomethyltartrate(4−) and dimethyltartrate(4−) ligands in frozen glasses at 77 K. Spin-Hamiltonian parameters have been obtained from the spectra collected for these triplet state species using an axial symmetry approximation. The fact that the zero-field splitting parameter, D, increases with increasing methyl substitution indicates a corresponding decrease in the metal-metal distance.

Electronic conductivity of AgI using D.C. polarization and charge transfer techniques

A Study of electronic conductivity using the d.c. polarization technique has been carried out in α and β-AgI which shows the former is a hole and the latter an electron conductor. Activation energies of undoped and Cu-doped single crystals and polycrystalline β-AgI were found to be 0.46 eV, 0.34 eV and 0.44 eV respectively and can be related to electron trap depths. The electron transference number ( σ θ σ t ) for polycrystalline β-AgI was found to be 0.008 at 306 K. The activation energy for hole conduction in α-AgI was determined to be 0.97 eV in agreement with previous XPS studies. Transient measurements have also been conducted using the charge transfer technique in double cells of polycrystalline β-AgI. The carrier concentration C θ and electron mobility μ θ, have thus been estimated to be 1.8 × 10 15 cm 3 and 5.14 × 10 −5 cm 2 V −sec. respectively at 306 K, while the double layer capacitance was 0.496 μF cm 2 .

Hg Cd Te mis structure: Modelling and application to charge-coupled device infrared imagery

Applications of CCD to read-out techniques signal processing of an infrared detector mosaic could lead to a new generation of sensors where the photosensor element density could be greatly increased. Due to their well-known detection capabilities in the 3–5μm and 8–15μm range, we have dealt with monolithic devices processed on the narrow bandgap semiconductor: mercury-cadmium-telluride. The project will assign optimization criteria which specify the device behaviour, i.e. spectral window, type of semiconductor material, temperature for definite working conditions, scanning and read-out procedure, signal processing. The first part of this paper develops the modelling of the elementary structure of the array designed for read-out through charge transfer techniques. This MIS structure can detect the incident infrared light and collect the corresponding signal charge. Limits imposed by collection and charge integration will modify the infrared system design: and we therefore deduce the specifications of such devices from the model. In the second part, the architecture and read-out mode of a two-dimensional matrix is presented. Choice between charge injection devices and charge-coupled devices should depend on the technology process and material properties, and is discussed with reference to the previous results. One solution worked out for the design of a 8 × 8 matrix array is described.

High sensitivity charge-transfer sense amplifier

A balanced charge-transfer sense amplifier for one-device cell memory arrays is presented. Charge-transfer techniques are used to preamplify the sense signal and to isolate the large bit/sense (B/S) line capacitance from the nodes of a dynamic latch. The high sensitivity of the sense-refresh amplifier is demonstrated in an experimental memory array with a B/S line to ell storage node capacitance ratio of 40 and a sense signal of about 61 mV. Performance limitations are also discussed.

Charge-transfer analogue-to-digital convertor

A novel means of implementing an analogue-to-digital conversion function by charge-transfer techniques is described. The number of metered charge packets that is required to fill a potential ‘well’ to a predetermined threshold level is linearly proportional to the magnitude of the input analogue voltage. Circuits have been implemented using p-channel, aluminium-gate technology, and have demonstrated 10–12 bits resolution capability.

Two-dimensional charge-transfer arrays

Charge-transfer arrays with a truly two-dimensional organization in which an element of information contained in a general cell can be moved in more than one direction to an adjacent cell are proposed. After a review of the basic electrode arrangements for various charge-transfer techniques, some possible layouts for actual devices are described. It is shown that simple orthogonal arrays could readily lead to mass serial/parallel converters. Other arrays in which not all unit cells are identical could perform more complicated processing such as mixing operations or passing maneuvers between two fields of information. The possibilities of building logic arrays and of using two-dimensional arrays in electrooptical systems are also discussed. It is concluded that the introduction of additional degrees of freedom into charge-transfer devices increases their versatility and their potential uses, and that technologies are available for the fabrication of two-dimensional arrays.

Intracell charge-transfer structures for signal processing

An approach is presented for implementing a fully programmable transversal filter using surface charge-transfer techniques. Summation of the signals from each output tap is performed automatically by using common output electrodes, and fixed binary tap weights are Provided by selectively controlling the transfer of charge within each cell. Charge packets representing a sampled data input signal are inserted into individual cells where they remain until they are replaced by a new sample. Any combination of these packets can be nondestructively read during any clock cycle with the output being automatically summed. Since the charge does not leave the cell, but is simply sloshed back and forth within it during a read-out cycle, charge-transfer losses are not cumulative in this structure. The application of these structures in various familiar signal-processing functions is discussed, and both experimental results and theoretical expressions for their performance are presented. Experimental results on a simple test cell include reading the same charge more than 5 × 105times and demonstrating a charge-transfer loss of less than 10-7per transfer.