Fluid dynamics modeling for synchronizing surface plasmon resonance and quartz crystal microbalance as tools for biomolecular and targeted drug delivery studies

We have used computational fluid dynamics modeling (CFD) to synchronize the flow conditions in the flow channels of two complementary surface-sensitive characterization techniques: surface plasmon resonance (SPR) and quartz crystal microbalance (QCM). Since the footprint of the flow channels of the two devices is specified by their function, the flow behavior can only be varied either by altering the height of the flow channel, or altering the volumetric rate of flow (flow rate) through the channel. The relevant quantity that must be calibrated is the shear strain on the measurement surface (center and bottom) of the flow channel. Our CFD modeling shows that the flow behavior is in the Stokes flow regime. We were thus able to generate a scaling expression with parameters for flow rate and flow channel height for each of the two devices: f(QCM)=2.64f(SPR)(h(QCM)/h(SPR)(2), where f(QCM) and f(SPR) are the flow rates in the SPR and QCM flow channels, respectively, and h(QCM)/h(SPR) is the ratio of the heights of the two channels. We demonstrate the success of our calibration procedure through the combined use of commercially available SPR and QCM flow channel devices on both a biomolecular interaction system of surface immobilized biotin and streptavidin and a targeted drug delivery model system of biotinylated liposomes interacting with a streptavidin functionalized surface.     

Quantitative irrationality for sums of reciprocals of Fibonacci and Lucas numbers

Irrationality measures are given for the values of the series , where and W_n is a rational valued Fibonacci or Lucas form, satisfying a second order linear recurrence. In particular, we prove irrationality of all the numbers

Ab initio studies on nanoscale friction between fluorinated diamond surfaces: effect of model size and level of theory

Interactions between two fluorinated diamond surfaces placed in contact with each other were investigated with quantum chemical Hartree-Fock and M?ller-Plesset perturbation theory and basis sets def-SV(P), def-TZVP, and 6-31G. Two models, C(6)H(6)F(3)-C(24)H(24)F(12) and C(13)H(16)F(6)-C(22)H(24)F(10), were used to examine how model size and level of theory affect the atomic-scale friction, especially the coefficient of friction. Also of interest was a comparison of the interaction energies of the two models with different stacking configurations. The averages of the calculated friction coefficients fell within the range of values 0.28-0.43.     

Kinetics of photoinduced electron transfer in polythiophene-porphyrin-fullerene molecular films

Photoinduced electron transfer (ET) processes were studied by the time-resolved Maxwell displacement charge (TRMDC) method in bilayer structures consisting of an electron donor-acceptor and conductive polymer monolayers, porphyrin-fullerene dyad and polyhexylthiophene, respectively, both layers prepared by the Langmuir-Blodgett (LB) method. The charge separation involves two fast steps: an intramolecular ET in the dyad molecule followed by an interlayer ET from the polymer to the formed porphyrin radical cation. These fast vertical intra- and interlayer processes could not be time-resolved by the TRMDC method. The lifetime of the charge separated state in the system was extended to hundreds of milliseconds by lateral electron and hole transfers in fullerene and polymer sublayers. The kinetics of the system was described by a model involving two long-living energetically different complete charge separated states. The data analysis indicates that the charge separation has a recombination time of 0.5 s. This is a promising result for possible applications.     

Correlation of electron self-energy with geometric structure in low-energy electron diffraction

In low-energy electron diffraction (LEED) studies of surface geometries where the energy dependence of the intensities is analyzed, the in-plane lattice parameter of the surface is usually set to a value determined by x-ray diffraction for the bulk crystal. In cases where it is not known, for instance in films that are incommensurate with the substrate, it is desirable to fit the in-plane lattice parameters in the same analysis as the perpendicular interlayer spacings. We show that this is not possible in a conventional LEED I(E) analysis because the inner potential, which is typically treated as an adjustable parameter, is correlated with the geometrical structure. Therefore, without having prior knowledge of the inner potential, it is not possible to determine the complete surface structure simply from LEED I(E) spectra, and the in-plane lattice parameter must be determined independently before the I(E) analysis is performed. This can be accomplished by establishing a more precise experimental geometry. Further, it is shown that the convention of omitting the energy dependency of the real part of the inner potential means geometrical LEED results cannot be trusted beyond a precision of approximately 0.01 ?.     

Temperature dependence of standard model CP violation

We analyze the temperature dependence of CP violation effects in the standard model by determining the effective action of its bosonic fields, obtained after integrating out the fermions from the theory and performing a covariant gradient expansion. We find nonvanishing CP violating terms starting at the sixth order of the expansion, albeit only in the C-odd-P-even sector, with coefficients that depend on quark masses, Cabibbo-Kobayashi-Maskawa matrix elements, temperature and the magnitude of the Higgs field. The CP violating effects are observed to decrease rapidly with temperature, which has important implications for the generation of a matter-antimatter asymmetry in the early Universe. Our results suggest that the cold electroweak baryogenesis scenario may be viable within the standard model, provided the electroweak transition temperature is at most of order 1 GeV.     

ChemInform Abstract: Icosahedral Au72: A Predicted Chiral and Spherically Aromatic Golden Fullerene

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