Application of differential reactivity towards synthesis of lamellarin and 8-oxoprotoberberine derivatives: Study of photochemical properties of aryl-substituted benzofuran-8-oxoprotoberberines

A unique differential reactivity between dihydroisoquinolines and 3-nitrocoumarins was observed and was exploited for the efficient construction of lamellarins and their isomeric benzofuran-8-oxoprotoberberine derivatives under acid-catalyzed or base-promoted conditions. Further, these prepared aryl-substituted benzofuran-8-oxoprotoberberine derivatives bearing electron-donating substituents on benzofuran moiety are found to be benchtop stable but light-sensitive, and can undergo oxidative ring-opening reaction to give the corresponding keto products when exposed to visible light under aerobic conditions.     

Study of Nonlinear Models of Oscillatory Systems by Applying an Intelligent Computational Technique

In this paper, we have analyzed the mathematical model of various nonlinear oscillators arising in different fields of engineering. Further, approximate solutions for different variations in oscillators are studied by using feedforward neural networks (NNs) based on the backpropagated Levenberg–Marquardt algorithm (BLMA). A data set for different problem scenarios for the supervised learning of BLMA has been generated by the Runge–Kutta method of order 4 (RK-4) with the “NDSolve” package in Mathematica. The worth of the approximate solution by NN-BLMA is attained by employing the processing of testing, training, and validation of the reference data set. For each model, convergence analysis, error histograms, regression analysis, and curve fitting are considered to study the robustness and accuracy of the design scheme.     

The use of contact angle measurements to estimate the adhesion propensity of calcium carbonate to solid substrates in water

We have studied a series of solids using contact angle measurements; stainless steel, gold, aluminium, titanium nitride and PTFE that are frequently used in domestic water environments. It was found the influence of electron-donor (γ⁻) and electron-acceptor (γ⁺) free energies on material scaling rate was dominated by water wetting angles, providing materials exhibit an average roughness below 100 nm. The γ⁻ component had the greatest influence on theoretical adhesion, while γ^LW, (Lifshitz-van der Waals) γ⁺ and γ^AB (acid-base) had little effect. From the materials analysed, amorphous carbon coatings were least adhesive, while ‘kettle coating’ and highly roughened steel the most adhesive. The size and distribution of asperities also influenced the polar free energies and subsequent adhesion due to fluctuations in the wetting angle. The results obtained indicate works of adhesion can be used as a complementary technique with Lewis acid-base theory to deliver useful information about the propensity of scale to deposit on solids.     

Rapid one-pot iterative diselenide–selenoester ligation using a novel coumarin-based photolabile protecting group

The development of an iterative one-pot peptide ligation strategy is described that capitalises on the rapid and efficient nature of the diselenide–selenoester ligation reaction, together with photodeselenisation chemistry. This ligation strategy hinged on the development of a novel photolabile protecting group for the side chain of selenocysteine, namely the 7-diethylamino-3-methyl coumarin (DEAMC) moiety. Deprotection of this DEAMC group can be effected in a mild, reagent-free manner using visible light (λ = 450 nm) without deleterious deselenisation of selenocysteine residues, thus enabling a subsequent ligation reaction without purification. The use of this DEAMC-protected selenocysteine in iterative DSL chemistry is highlighted through the efficient one-pot syntheses of 60- and 80-residue fragments of mucin-1 as well as apolipoprotein CIII in just 2–4 hours.

A method for the rapid one-pot iterative assembly of proteins via diselenide–selenoester ligation (DSL) chemistry is described that capitalises on a novel coumarin-based photolabile protecting group for selenocysteine.     

A quantum pseudodot system with two-dimensional pseudoharmonic oscillator in external magnetic and Aharonov-Bohm fields

Using the Nikiforov–Uvarov (NU) method, the energy levels and the wave functions of an electron confined in a two-dimensional (2D) pseudoharmonic quantum dot are calculated under the influence of temperature and an external magnetic field inside dot and Aharonov–Bohm (AB) field inside a pseudodot. The exact solutions for energy eigenvalues and wave functions are computed as functions of the chemical potential parameters, applied magnetic field strength, AB flux field, magnetic quantum number and temperature. Analytical expression for the light interband absorption coefficient and absorption threshold frequency are found as functions of applied magnetic field and geometrical size of quantum pseudodot. The temperature dependence energy levels for GaAs semiconductor are also calculated.     

Reversal of Klein reflection by magnetic barriers in bilayer graphene

Massless Dirac fermions in monolayer graphene exhibit total transmission when normally incident on a scalar potential barrier, a consequence of the Klein paradox originally predicted by O Klein for relativistic electrons obeying the 3 + 1 dimensional Dirac equation. For bilayer graphene, charge carriers are massive Dirac fermions and, due to different chiralities, electron and hole states are not coupled to each other. Therefore, the wavefunction of an incident particle decays inside a barrier as for the non-relativistic Schr?dinger equation. This leads to exponentially small transmission upon normal incidence. We show that, in the presence of magnetic barriers, such massive Dirac fermions can have transmission even at normal incidence. The general consequences of this behavior for multilayer graphene consisting of massless and massive modes are mentioned. We also briefly discuss the effect of a bias voltage on such magnetotransport.     

Development and validation of a UV-spectrophotometric method for the determination of pheniramine maleate and its stability studies

A sensitive, precise, and cost-effective UV-spectrophotometric method is described for the determination of pheniramine maleate (PAM) in bulk drug and tablets. The method is based on the measurement of absorbance of a PAM solution in 0.1 N HCl at 264 nm. As per the International Conference on Harmonization (ICH) guidelines, the method was validated for linearity, accuracy, precision, limits of detection (LOD) and quantification (LOQ), and robustness and ruggedness. A linear relationship between absorbance and concentration of PAM in the range of 2–40 μg/ml with a correlation coefficient (r) of 0.9998 was obtained. The LOD and LOQ values were found to be 0.18 and 0.39 μg/ml PAM, respectively. The precision of the method was satisfactory: the value of relative standard deviation (RSD) did not exceed 3.47%. The proposed method was applied successfully to the determination of PAM in tablets with good accuracy and precision. Percentages of the label claims ranged from 101.8 to 102.01% with the standard deviation (SD) from 0.64 to 0.72%. The accuracy of the method was further ascertained by recovery studies via a standard addition procedure. In addition, the forced degradation of PAM was conducted in accordance with the ICH guidelines. Acidic and basic hydrolysis, thermal stress, peroxide, and photolytic degradation were used to assess the stability-indicating power of the method. A substantial degradation was observed during oxidative and alkaline degradations. No degradation was observed under other stress conditions.     

Effects of external fields on a two-dimensional Klein-Gordon particle under pseudo-harmonic oscillator interaction

We study the effects of the perpendicular magnetic and Aharonov-Bohm(AB) flux fields on the energy levels of a two-dimensional(2D) Klein-Gordon(KG) particle subjected to an equal scalar and vector pseudo-harmonic oscillator(PHO).We calculate the exact energy eigenvalues and normalized wave functions in terms of chemical potential parameter,magnetic field strength,AB flux field,and magnetic quantum number by means of the Nikiforov-Uvarov(NU) method.The non-relativistic limit,PHO,and harmonic oscillator solutions in the existence and absence of external fields are also obtained.     

Approximate <Emphasis Type="Italic">κ</Emphasis>-state solutions to the Dirac-Yukawa problem based on the spin and pseudospin symmetry

Using an approximation scheme to deal with the centrifugal (pseudo-centrifugal) term, we solve the Dirac equation with the screened Coulomb (Yukawa) potential for any arbitrary spin-orbit quantum number κ. Based on the spin and pseudospin symmetry, analytic bound state energy spectrum formulas and their corresponding upper- and lower-spinor components of two Dirac particles are obtained using a shortcut of the Nikiforov-Uvarov method. We find a wide range of permissible values for the spin symmetry constant C _s from the valence energy spectrum of particle and also for pseudospin symmetry constant C _ps from the hole energy spectrum of antiparticle. Further, we show that the present potential interaction becomes less (more) attractive for a long (short) range screening parameter α. To remove the degeneracies in energy levels we consider the spin and pseudospin solution of Dirac equation for Yukawa potential plus a centrifugal-like term. A few special cases such as the exact spin (pseudospin) symmetry Dirac-Yukawa, the Yukawa plus centrifugal-like potentials, the limit when α becomes zero (Coulomb potential field) and the non-relativistic limit of our solution are studied. The nonrelativistic solutions are compared with those obtained by other methods.