All-Solid-State PVC Membrane Ag+-Selective Electrodes Based on Diaza-18-Crown-6 Compounds

Two diaza-crown ether compounds were synthesized and evaluated as Ag⁺-selective carriers in polyvinylchloride (PVC) membrane electrodes of solid-state type. The all-solid-state PVC membrane electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 exhibited a super-Nernstian response (75±10mV per decade) over the concentration range of 1×10^–1 to 7×10^–6M of Ag⁺ ion and a detection limit of 3×10^–6M, at a wide range of pH (pH 4–7). The response time of the electrode was fast (less than 10s), and it can be used for three months without any significant deviation in potential. The proposed all-solid-state PVC membrane electrodes revealed high selectivity toward Ag⁺ ion with respect to alkali, alkaline earth, heavy and transition metal ions. A flow-through cell of all-solid-state PVC membrane Ag⁺-selective electrode based on N,N-Dibenzyl-dibenzo-diaza-18-crown-6 has also been prepared and applied for flow-injection analysis of Ag⁺ ion in solution.     

Discrete-Time Pricing and Optimal Exercise of American Perpetual Warrants in the Geometric Random Walk Model

An American option (or, warrant) is the right, but not the obligation, to purchase or sell an underlying equity at any time up to a predetermined expiration date for a predetermined amount. A perpetual American option differs from a plain American option in that it does not expire. In this study, we solve the optimal stopping problem of a perpetual American option (both call and put) in discrete time using linear programming duality. Under the assumption that the underlying stock price follows a discrete time and discrete state Markov process, namely a geometric random walk, we formulate the pricing problem as an infinite dimensional linear programming (LP) problem using the excessive-majorant property of the value function. This formulation allows us to solve complementary slackness conditions in closed-form, revealing an optimal stopping strategy which highlights the set of stock-prices where the option should be exercised. The analysis for the call option reveals that such a critical value exists only in some cases, depending on a combination of state-transition probabilities and the economic discount factor (i.e., the prevailing interest rate) whereas it ceases to be an issue for the put.     

Standardized method comparison for ACS:180 plus and Immulite sensitive PSA (sPSA) measurement methods

The aim of this study was to compare two immunoassay measurement methods, the ACS:180 Plus (Chiron Diagnostics) kit and the Immulite sPSA (DPC) kit. Method comparison analysis was performed according to EP9-A; approved guideline of NCCLS 51. Serum samples having a wide range of total prostate-specific antigen (PSA) concentrations were evaluated in split-sample analysis. F-test, t-test analysis and regression statistics were performed. In Deming regression analysis the coefficients were as follows; the slope=0.967; y-intercept=-0.148, r=0.989. An acceptable bias was seen since the systematical error was calculated to have a value less than the total allowable error calculated from biological variations. Non-parametric evaluation of the area under ROC curves for ACS:180 Plus and Immulite sPSA were 0.997 and 0.987, respectively. Diagnostic accuracy was at the level of p= 0.000 and no statistical difference was found between the two assay methods.     

Solution to transient Navier–Stokes equations by the coupling of differential quadrature time integration scheme with dual reciprocity boundary element method

The two‐dimensional time‐dependent Navier–Stokes equations in terms of the vorticity and the stream function are solved numerically by using the coupling of the dual reciprocity boundary element method (DRBEM) in space with the differential quadrature method (DQM) in time. In DRBEM application, the convective and the time derivative terms in the vorticity transport equation are considered as the nonhomogeneity in the equation and are approximated by radial basis functions. The solution to the Poisson equation, which links stream function and vorticity with an initial vorticity guess, produces velocity components in turn for the solution to vorticity transport equation. The DRBEM formulation of the vorticity transport equation results in an initial value problem represented by a system of first‐order ordinary differential equations in time. When the DQM discretizes this system in time direction, we obtain a system of linear algebraic equations, which gives the solution vector for vorticity at any required time level. The procedure outlined here is also applied to solve the problem of two‐dimensional natural convection in a cavity by utilizing an iteration among the stream function, the vorticity transport and the energy equations as well. The test problems include two‐dimensional flow in a cavity when a force is present, the lid‐driven cavity and the natural convection in a square cavity. The numerical results are visualized in terms of stream function, vorticity and temperature contours for several values of Reynolds (Re) and Rayleigh (Ra) numbers. Copyright © 2008 John Wiley & Sons, Ltd.     

Orbital-optimized third-order Møller-Plesset perturbation theory and its spin-component and spin-opposite scaled variants: application to symmetry breaking problems

In this research, orbital-optimized third-order M?ller-Plesset perturbation theory (OMP3) and its spin-component and spin-opposite scaled variants (SCS-OMP3 and SOS-OMP3) are introduced. Using a Lagrangian-based approach, an efficient, quadratically convergent algorithm for variational optimization of the molecular orbitals (MOs) for third-order M?ller-Plesset perturbation theory (MP3) is presented. Explicit equations for response density matrices, the MO gradient, and Hessian are reported in spin-orbital form. The OMP3, SCS-OMP3, and SOS-OMP3 approaches are compared with the second-order M?ller-Plesset perturbation theory (MP2), MP3, coupled-cluster doubles (CCD), optimized-doubles (OD), and coupled-cluster singles and doubles (CCSD) methods. All these methods are applied to the O(4)(+), O(3), and seven diatomic molecules. Results demonstrate that the OMP3 and its variants provide significantly better vibrational frequencies than MP3, CCSD, and OD for the molecules where the symmetry-breaking problems are observed. For O(4)(+), the OMP3 prediction, 1343 cm(-1), for ω(6) (b(3u)) mode, where symmetry-breaking appears, is even better than presumably more reliable methods such as Brueckner doubles (BD), 1194 cm(-1), and OD, 1193 cm(-1), methods (the experimental value is 1320 cm(-1)). For O(3), the predictions of SCS-OMP3 (1143 cm(-1)) and SOS-OMP3 (1165 cm(-1)) are remarkably better than the more robust OD method (1282 cm(-1)); the experimental value is 1089 cm(-1). For the seven diatomics, again the SCS-OMP3 and SOS-OMP3 methods provide the lowest average errors, ∣Δω(e)∣ = 44 and ∣Δω(e)∣ = 35 cm(-1), respectively, while for OD, ∣Δω(e)∣ = 161 cm(-1)and CCSD ∣Δω(e)∣ = 106 cm(-1). Hence, the OMP3 and especially its spin-scaled variants perform much better than the MP3, CCSD, and more robust OD approaches for considered test cases. Therefore, considering both the computational cost and the reliability, SCS-OMP3 and SOS-OMP3 appear to be the best methods for the symmetry-breaking cases, based on present application results. The OMP3 method offers certain advantages: it provides reliable vibrational frequencies in case of symmetry-breaking problems, especially with spin-scaling tricks, its analytic gradients are easier to compute since there is no need to solve the coupled-perturbed equations for the orbital response, and the computation of one-electron properties are easier because there is no response contribution to the particle density matrices. The OMP3 has further advantages over standard MP3, making it promising for excited state properties via linear response theory.     

Semi‐analytical solution of MHD flow through boundary integrals on the pipe wall

A mathematical model is given for the magnetohydrodynamic (MHD) pipe flow as an inner Dirichlet problem in a 2D circular cross section of the pipe, coupled with an outer Dirichlet or Neumann magnetic problem. Inner Dirichlet problem is given as the coupled convection‐diffusion equations for the velocity and the induced current of the fluid coupling also to the outer problem, which is defined with the Laplace equation for the induced magnetic field of the exterior region with either Dirichlet or Neumann boundary condition. Unique solution of inner Dirichlet problem is obtained theoretically reducing it into two boundary integral equations defined on the boundary by using the corresponding fundamental solutions. Exterior solution is also given theoretically on the pipe wall with Poisson integral, and it is unique with Dirichlet boundary condition but exists with an additive constant obtained through coupled boundary and solvability conditions in Neumann wall condition. The collocation method is used to discretize these boundary integrals on the pipe wall. Thus, the proposed procedure is an improved theoretical analysis for combining the solution methods for the interior and exterior regions, which are consolidated numerically showing the flow behavior. The solution is simulated for several values of problem parameters, and the well‐known MHD characteristics are observed inside the pipe for increasing values of Hartmann number maintaining the continuity of induced currents on the pipe wall.     

A low-cost,fast, disposable and sensitive biosensor study: flow injection analysis of glucose at poly-methylene blue-modified pencil graphite electrode

In this work, firstly methylene blue (MB) was electropolymerized onto pencil graphite electrode (PGE) surface for the electrocatalytic oxidation of NADH. Cyclic voltammograms show that oxidation potential of NADH at Poly-MB/PGE shifted to negative direction about 300 mV compared with bare PGE. These results indicate that Poly-MB/PGE exhibits a good electrocatalytic activity toward NADH oxidation. Then, a glucose biosensor study was performed based on the determination of enzymatically generated NADH by glucose dehydrogenase (GDH) which immobilized onto Poly-MB/PGE using glutaraldehyde cross-linking procedure. The biosensing of glucose in flow injection analysis (FIA) system was performed at GDH/Poly-MB/PGE for the first time. The electrocatalytic oxidation currents of enzymatically produced NADH obtained from FI amperometric current–time curves recorded at + 200 mV and in phosphate buffer solution at pH 7.0 containing 1.0 M KCl were linearly related to the concentration of glucose. Linear calibration plots are obtained in the concentration range from 0.01 to 1.0 mM. The limit of detection (LOD) was found to be 4.0 µM. A fast, sensitive, low-cost and disposable glucose biosensor was constructed in FIA system using GDH/Poly-MB/PGE; therefore, it might provide a new perspective for the fabrication of biosensor of other compounds such as glutamate, lactate and alcohol.     

Voltammetric Determination of Favipiravir Used as an Antiviral Drug for the Treatment of Covid-19 at Pencil Graphite Electrode

This work describes the sensitive voltammetric determination of favipiravir (FAV) based on its reduction for the first time with a low-cost and disposable pencil graphite electrode (PGE). In addition, the determination of FAV was also performed based on its oxidation. Differential pulse (DP) voltammograms recorded in 0.5 M H₂SO₄ for the reduction of FAV show that peak currents increase linearly in the range of 1.0 to 600.0 μM with a limit of detection of 0.35 μM. The acceptable recovery values (98.9–106.0 %) obtained from a pharmaceutical tablet, real human urine, and artificial blood serum samples spiked with FAV confirm the high accuracy of the proposed method.     

Theoretical study of thermal rearrangements of 1-hexen-5-yne, 1,2,5-hexatriene, and 2-methylenebicyclo[2.1.0]pentane

In this research, a comprehensive theoretical investigation of the thermal rearrangements of 1-hexen-5-yne, 1,2,5-hexatriene, and 2-methylenebicyclo[2.1.0]pentane is carried out employing density functional theory (DFT) and high level ab initio methods, such as the complete active space self-consistent field (CASSCF), multireference second-order M?ller-Plesset perturbation theory (MRMP2), and coupled-cluster singles and doubles with perturbative triples [CCSD(T)]. The potential energy surface (PES) for the relevant system is explored to provide a theoretical account of pyrolysis experiments by Huntsman, Baldwin, and Roth on the target system. The rate constants and product distributions are calculated using theoretical kinetic modelings. The rate constant for each isomerization reaction is computed using the transition state theory (TST). The simultaneous first-order ordinary-differential equations are solved numerically for the relevant system to obtain time-dependent concentrations, hence the product distributions at a given temperature. Our computed energy values (reaction energies and activation parameters) are in agreement with Roth's experiments and the product distributions of Huntsman's experiments at 340 and 385 °C with various reaction times, while simulated product fractions are in qualitative accordance with Baldwin's experiment.     

The lowest-lying electronic singlet and triplet potential energy surfaces for the HNO-NOH system: energetics, unimolecular rate constants, tunneling and kinetic isotope effects for the isomerization and dissociation reactions

The lowest-lying electronic singlet and triplet potential energy surfaces (PES) for the HNO-NOH system have been investigated employing high level ab initio quantum chemical methods. The reaction energies and barriers have been predicted for two isomerization and four dissociation reactions. Total energies are extrapolated to the complete basis set limit applying focal point analyses. Anharmonic zero-point vibrational energies, diagonal Born-Oppenheimer corrections, relativistic effects, and core correlation corrections are also taken into account. On the singlet PES, the (1)HNO → (1)NOH endothermicity including all corrections is predicted to be 42.23 ± 0.2 kcal mol(-1). For the barrierless decomposition of (1)HNO to H + NO, the dissociation energy is estimated to be 47.48 ± 0.2 kcal mol(-1). For (1)NOH → H + NO, the reaction endothermicity and barrier are 5.25 ± 0.2 and 7.88 ± 0.2 kcal mol(-1). On the triplet PES the reaction energy and barrier including all corrections are predicted to be 7.73 ± 0.2 and 39.31 ± 0.2 kcal mol(-1) for the isomerization reaction (3)HNO → (3)NOH. For the triplet dissociation reaction (to H + NO) the corresponding results are 29.03 ± 0.2 and 32.41 ± 0.2 kcal mol(-1). Analogous results are 21.30 ± 0.2 and 33.67 ± 0.2 kcal mol(-1) for the dissociation reaction of (3)NOH (to H + NO). Unimolecular rate constants for the isomerization and dissociation reactions were obtained utilizing kinetic modeling methods. The tunneling and kinetic isotope effects are also investigated for these reactions. The adiabatic singlet-triplet energy splittings are predicted to be 18.45 ± 0.2 and 16.05 ± 0.2 kcal mol(-1) for HNO and NOH, respectively. Kinetic analyses based on solution of simultaneous first-order ordinary-differential rate equations demonstrate that the singlet NOH molecule will be difficult to prepare at room temperature, while the triplet NOH molecule is viable with respect to isomerization and dissociation reactions up to 400 K. Hence, our theoretical findings clearly explain why (1)NOH has not yet been observed experimentally.