Spectral tuning in visual pigments: an ONIOM(QM:MM) study on bovine rhodopsin and its mutants

We have investigated geometries and excitation energies of bovine rhodopsin and some of its mutants by hybrid quantum mechanical/molecular mechanical (QM/MM) calculations in ONIOM scheme, employing B3LYP and BLYP density functionals as well as DFTB method for the QM part and AMBER force field for the MM part. QM/MM geometries of the protonated Schiff-base 11- cis-retinal with B3LYP and DFTB are very similar to each other. TD-B3LYP/MM excitation energy calculations reproduce the experimental absorption maximum of 500 nm in the presence of native rhodopsin environment and predict spectral shifts due to mutations within 10 nm, whereas TD-BLYP/MM excitation energies have red-shift error of at least 50 nm. In the wild-type rhodopsin, Glu113 shifts the first excitation energy to blue and accounts for most of the shift found. Other amino acids individually contribute to the first excitation energy but their net effect is small. The electronic polarization effect is essential for reproducing experimental bond length alternation along the polyene chain in protonated Schiff-base retinal, which correlates with the computed first excitation energy. It also corrects the excitation energies and spectral shifts in mutants, more effectively for deprotonated Schiff-base retinal than for the protonated form. The protonation state and conformation of mutated residues affect electronic spectrum significantly. The present QM/MM calculations estimate not only the experimental excitation energies but also the source of spectral shifts in mutants.     

Voltammetric Behavior of Testosterone on Bismuth Film Electrode: Highly Sensitive Determination in Pharmaceuticals and Human Urine by Square‐Wave Adsorptive Stripping Voltammetry

In this paper, an electrochemical application of bismuth‐film electrode (BiFE) fabricated via ex‐situ electrodeposition onto a glassy carbon electrode for testosterone determination was investigated in aqueous and aqueous/surfactant solutions. In cyclic voltammetry, the compound showed one irreversible and adsorption‐controlled reduction peak. The BiFE revealed good linear response in the examined concentration range of 1 to 45 nmol L^?1 testosterone in Britton? Robinson buffer, pH 5.0 containing 3 mmol L^?1 cetyltrimethylammonium bromide. The limit of detection was 0.3 nmol L^?1 (0.09 ng mL^?1). Finally, the BiFE was satisfactorily applied for quantitation of testosterone in both pharmaceutical (oil‐based ampoule) and biological (human urine) samples.     

Flow and heat transfer over a rotating porous disk in a nanofluid

The steady flow of an incompressible viscous fluid due to a rotating disk in a nanofluid is studied. The transformed boundary layer equations are solved numerically by a finite difference scheme, namely the Keller-box method. Numerical results for the flow and heat transfer characteristics are obtained for various values of the nanoparticle volume fraction parameter φ and suction/injection parameter h₀. Two models for the effective thermal conductivity of the nanofluid, namely the Maxwell-Garnett model and the Patel model, are considered. It is found that for the Patel model, the heat transfer rate at the surface increases for both suction and injection, whereas different behaviors are observed for the Maxwell-Garnett model, i.e. increasing the values of φ leads to a decrease in the heat transfer rate at the surface for suction, but increases for injection. The results of this study can be used in the design of an effective cooling system for electronic components to help ensure effective and safe operational conditions.     

NORM activity concentration in sediment cores from the Peninsular Malaysia East Coast Exclusive Economic Zone

Study for distribution of Naturally Occurring Radioactive Materials (NORM) i.e. ²²⁶Ra, ²²⁸Ra and ⁴⁰K in the east coast of Peninsular Malaysia Exclusive Economic Zone (EEZ) was carried out as part of the national marine environment project. Sixteen marine sediment cores from selected locations within the EEZ were collected for determination of NORM activity concentrations using high-purity germanium (HPGe) gamma spectrometer. From the measurement, the activity concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K is ranged from 16 ± 4 Bq/kg to 46 ± 6 Bq/kg (total mean 30), 28 ± 7 Bq/kg to 87 ± 11 Bq/kg (total mean 56) and 171 ± 33 Bq/kg to 690 ± 89 Bq/kg (total mean 420), dry wt., respectively. The activity concentrations of radionuclides in most of the core were quite uniform suggesting that there were thorough vertical mixed of sediment throughout the core. The results obtained were also in good agreement with those previous reported from other countries in the region and therefore can be used to enhance present radioactivity database. The calculated external hazard values were ranged from 0.25 to 0.51 with the mean of 0.38 (less than unity) showed little risk of external hazard to the workers handling the sediments and it was likely low level of the mainland natural gamma-radiation in the east coast of Peninsular Malaysia.     

Effects of hydrolysis conditions on the morphology,crystallinity, and thermal stability of cellulose nanocrystals extracted from kenaf bast fibers

Cellulose nanocrystals (CNC) were first isolated from kenaf bast fibers and then characterized. The raw fibers were subjected to alkali treatment and bleaching treatment and subsequent hydrolysis with sulfuric acid. The influence of the reaction time on the morphology, crystallinity, and thermal stability of CNC was investigated. Fourier transform infrared spectroscopy showed that lignin and hemicellulose were almost entirely removed during the alkali and bleaching treatments. The morphology and dimensions of the fibers and acid-released CNC were characterized by field emission scanning electron microscopy and transmission electron microscopy. X-Ray diffraction analysis revealed that the crystallinity first increases upon hydrolysis and then decreases after long durations of hydrolysis. The optimal extraction time was found to be around 40 min during hydrolysis at 45 °C with 65% sulfuric acid. The thermal stability was found to decrease as the hydrolysis time increased. The electrophoretic mobility of the CNC suspensions was measured using the zeta potential, and it ranged from −8.7 to −95.3 mV.     

Elements of Mechanics,by P.F. Kelly

Applications of optogalvanic spectroscopy developed since the resurgence of interest in optogalvanic detection are reviewed. The optogalvanic effect is a change in the electrical properties of a discharge caused by illuminating the discharge with radiation having a wavelength corresponding to an atomic or molecular transition in the discharge. The general scheme of optogalvanic spectroscopy is presented, followed by a discussion of the gas discharge physics of the optogalvanic effect. Applications of optogalvanic detection in moderate resolution spectroscopy, in Doppler-free spectroscopy, and in analytic studies are discussed.     

Book reviews

Boundary Layers of Flow and Temperature. By Alfred Walz. (The M.I.T. Press, 1970.) [Pp. 297.] £8.4. Scope: Treatise/textbook Level: Specialist/postgraduate.

Interpretation of X-ray Powder Diffractian Pattern. By H. Lipson and H. Steeple. (London: Macmillan; New York: St. Martin's Press, 1970.) [Pp. viii + 335.1 £4.00. Scope: Textbook. Level: Specialist.     

Photophysical and Analyte Sensing Properties of Cyclometalated Ir(III) Complexes

The synthesis of some heteroleptic, cyclometalated iridium(III) complexes is described. The utility of these [Ir(ppy)₂(N-N)]Cl (ppy = 2-phenylpyridine and N-N = substituted bipyridine, biquinoline, or phenanthroline) complexes as luminescence-based sensors is assessed. The emission intensity of an Ir(III) complex featuring the 3,3′-H_ndcbpy ligand (H_ndcbpy = dicarboxylic acid-2,2′-bipyridine; n = 0,1,2 to indicate deprotonated, mono- and diprotonated species, respectively) is seen to increase in the presence of Pb(II). Insight into the structure and analyte-sensing capability is achieved by X-ray crystallography in conjunction with computational modeling. Complexes incorporating carboxylic acid-functionalized bipyridine and biquinoline as the polypyridyl ligand show pH sensitivity while similar phenanthroline complexes do not.     

Flow and heat transfer of nanofluid past stretching/shrinking sheet with partial slip boundary conditions

The boundary layer flow of a nanofluid past a stretching/shrinking sheet with hydrodynamic and thermal slip boundary conditions is studied. Numerical solutions to the governing equations are obtained using a shooting method. The results are found for the skin friction coefficient, the local Nusselt number, and the local Sherwood number as well as the velocity, temperature, and concentration profiles for some values of the velocity slip parameter, thermal slip parameter, stretching/shrinking parameter, thermophoresis parameter, and Brownian motion parameter. The results show that the local Nusselt number, which represents the heat transfer rate, is lower for higher values of thermal slip parameter, thermophoresis parameter, and Brownian motion parameter.