Noble-metal nanoparticles directly conjugated to globular proteins

We report the synthesis of gold nanoparticles directly conjugated to bovine serum albumin protein by chemical reduction in aqueous solution. Transmission electron microscopy reveals that the gold nanoparticles are well dispersed with an average diameter less than 2 nm, and elemental analysis verifies the composition of the gold-protein conjugates. Infrared spectroscopy confirms that the polypeptide backbone is not cleaved during the conjugation process and that the side chain functional groups remain intact. Raman spectroscopy demonstrates that the disulfide bonds in the conjugated protein are broken and thus are available for interaction with the nanoparticle surface. This synthesis method is a new technique for directly attaching gold nanoparticles to macromolecular proteins.     

High-performance liquid chromatographic analysis of Romet-30 in salmon following administration of medicated feed

A sensitive and selective high-performance liquid chromatographic assay was developed for the simultaneous quantitation of sulphadimethoxine (SDM) and ormetoprim (OMP) in chinook salmon muscle tissue. SDM and OMP were extracted from tissue samples using a solid-phase extraction technique. Resolution of both drugs was accomplished using an Ultrasphere ion-pair column (250 x 4.6 mm I.D.) and a mobile phase of acetonitrile-methanol-0.1 M phosphate buffer, pH 4 (17:10:73) with ultraviolet detection at 280 nm. The calibration curve in salmon muscle tissue was linear over the concentration range 0.2-20 ppm for both SDM (r2 = 0.9974) and OMP (r2 = 0.9956). The minimum detectable quantity of SDM and OMP in salmon muscle tissue was 0.2 ppm at a signal-to-noise ratio of 5:1. An in vivo feeding experiment was undertaken where chinook salmon were administered Romet-30-medicated feed for a 10-day period, followed by a 42-day wash-out period. The rate of tissue uptake and decline of SDM and OMP was shown to differ.     

Flexible effective fragment QM/MM method: validation through the challenging tests

A new version of the QM/MM method, which is based on the effective fragment potential (EFP) methodology [Gordon, M. et al., J Phys Chem A 2001, 105, 293] but allows flexible fragments, is verified through calculations of model molecular systems suggested by different authors as challenging tests for QM/MM approaches. For each example, the results of QM/MM calculations for a partitioned system are compared to the results of an all-electron ab initio quantum chemical study of the entire system. In each case we were able to achieve approximately similar or better accuracy of the QM/MM results compared to those described in original publications. In all calculations we kept the same set of parameters of our QM/MM scheme. A new test example is considered when calculating the potential of internal rotation in the histidine dipeptide around the C(alpha)bond;C(beta) side chain bond.     

EFFECT OF RECEIVER ORIENTATION ON ERYTHEMA DOSE1,2

-The analysis of solar erythema dose under changing ozone amount, previously confined to the study of horizontal surfaces, is extended to include the effects of receiver orientation. A semi-empirical model is used to calculate erythema (sunburn) dose for non-horizontal plane areas under cloudless conditions as a function of latitude, season, and ozone amount. According to the model, in middle and high latitudes, surfaces with inclination angles (α) up to 45° receive at least 80% of the daily erythema dose received by a horizontal surface. Much larger reductions in daily erythema dose occur for α > 45°. which can result in a significant reduction in the latitudinal gradient of erythema dose. The amplification factor for erythema dose (Δdose/ΔO₃) varies significantly with latitude, but it is only weakly dependent upon receiver orientation. Additional calculations indicate that the amplification factor may be significantly larger for skin cancer than for erythema.     

Synthesis and micellar characterization of short block length methoxy poly(ethylene glycol)-block-poly(caprolactone) diblock copolymers

A series of short block length methoxy poly(ethylene glycol)-block-poly(caprolactone) diblock copolymers was synthesized and characterized in order to assess the potential of these copolymers as a micellar drug-delivery system. Varying the caprolactone:MePEG weight ratio in the reaction mixture allowed the synthesis of diblock copolymers with a MePEG molecular weight of 750 g/mol and PCL block lengths of 2, 5 or 10 repeat units. Phase diagrams of aqueous solutions of the copolymers were constructed which displayed characteristic cloud points and Krafft points. As the degree of polymerization of PCL increased, critical micelle concentration (CMC) values decreased from 6.97 x 10(-1) to 3.38 x 10(-3) g/l, partition equilibrium coefficients (Kv) increased from 1.09 x 10(4) to 22.2 x 10(4),and hydrodynamic diameters increased from 12.2 to 19.5 nm. The micelle morphology was determined to be spherical by transmission electron microscopy.     

Inertial solvent dynamics and the analysis of spectral line shapes: Temperature-dependent absorption spectrum of beta-carotene in nonpolar solvent

The influence of solvent dynamics on optical spectra is often described by a stochastic model which assumes exponential relaxation of the time-correlation function for solvent-induced frequency fluctuations. In contrast, theory and experiment suggest that the initial (subpicosecond) phase of solvent relaxation, resulting from inertial motion of the solvent, is a Gaussian function of time. In this work, we employ numerical and analytical calculations to compare the predicted absorption line shapes and the derived solvent reorganization energies obtained from exponential (Brownian oscillator) versus Gaussian (inertial) solvent dynamics. Both models predict motional narrowing as the ratio kappa = Lambda/Delta is increased, where Lambda and Delta are the frequency and variance, respectively, of the solvent-induced frequency fluctuations. However, the motional narrowing limit is achieved at lower values of kappa for the Brownian oscillator model compared to the inertial model. For a given line shape, the derived value of the solvent reorganization energy lambdasolv is only weakly dependent on the solvent relaxation model employed, though different solvent parameters Lambda and Delta are obtained. The two models are applied to the analysis of the temperature-dependent absorption spectrum of beta-carotene in isopentane and CS2. The derived values of lambdasolv using the Gaussian model are found to be in better agreement with the high temperature limit of Delta2/2kBT than are the values obtained using the Brownian oscillator model. In either approach, the solvent reorganization energy is found to increase slightly with temperature as a result of an increase in the variance Delta of the solvent-induced frequency fluctuations.     

A low diffusion particle method for simulating compressible inviscid flows

A new particle method is presented for the numerical simulation of compressible inviscid gas flows, through procedures which involve relatively small modifications to an existing direct simulation Monte Carlo (DSMC) algorithm. Implementation steps are outlined for simulations involving various grid geometries and for gas mixtures comprising an arbitrary number of species. The proposed method is compared with other numerical schemes through a series of one-dimensional and two-dimensional test cases, and is shown to provide a significant reduction in both artificial diffusion and statistical scatter effects relative to existing DSMC-based equilibrium particle methods.     

Tractor tire aspect ratio effects on soil bulk density and cone index

A 580/70R38 tractor drive tire with an aspect ratio of 0.756 and a 650/75R32 tire with an aspect ratio of 0.804 were operated at two dynamic loads and two inflation pressures on a sandy loam and a clay loam with loose soil above a hardpan. Soil bulk density and cone index were measured just above the hardpan beneath the centerline and edge of the tires. The bulk densities were essentially equal for the two tires and cone indices were also essentially equal for the two tires. Soil bulk density and cone index increased with increasing dynamic load at constant inflation pressure, and with increasing inflation pressure at constant dynamic load. In comparisons of the centerline and edge locations, soil bulk density and cone index were significantly less beneath the edge than beneath the centerline of the tires. Soil compaction is not likely to be affected by the aspect ratio of radial-ply tractor drive tires when aspect ratios are between 0.75 and 0.80.     

A hybrid particle approach for continuum and rarefied flow simulation

A hybrid particle scheme is presented for the simulation of compressible gas flows involving both continuum regions and rarefied regions with strong translational nonequilibrium. The direct simulation Monte Carlo (DSMC) method is applied in rarefied regions, while remaining portions of the flowfield are simulated using a DSMC-based low diffusion particle method for inviscid flow simulation. The hybrid scheme is suitable for either steady state or unsteady flow problems, and can simulate gas mixtures comprising an arbitrary number of species. Numerical procedures are described for strongly coupled two-way information transfer between continuum and rarefied regions, and additional procedures are outlined for the determination of continuum breakdown. The hybrid scheme is evaluated through a comparison with DSMC simulation results for a Mach 6 flow of N₂ over a cylinder, and good overall agreement is observed. Large potential efficiency gains (over three orders of magnitude) are estimated for the hybrid algorithm relative to DSMC in a simple example involving a rarefied expansion flow through a small nozzle into a vacuum chamber.     

Vector Bundle Moduli

We give the general presciption for calculating the number of moduli of irreducible, stable U(n) holomorphic vector bundles with positive spectral covers over elliptically fibered Calabi–Yau threefolds. Explicit results are presented for Hirzebruch base surfaces B = F _r. Vector bundle moduli appear as gauge singlet scalar fields in the effective low-energy actions of heterotic superstrings and heterotic M-theory.