van der Waals interactions of polycyclic aromatic hydrocarbon dimers

Density functional theory is in principle exact and includes also long-range interactions, such as the van der Waals interactions. These are, however, part of the exchange-correlation energy functional that needs to be approximated, and are absent in the local and semilocal standard implementations. Recently a density functional which includes van der Waals interactions for planar systems has been developed, which we show can be extended to provide a treatment of planar molecules. We use this functional to calculate binding distances and energies for dimers of three of the smallest polycyclic aromatic hydrocarbons (PAHs)--naphthalene, anthracene, and pyrene.     

Infrared spectra and relative stability of the F3CH/NH3 H-bonded complex in liquefied Xe

FTIR spectra of mixtures of fluoroform (F3CH) and ammonia (NH3), have been studied in liquid xenon between 5400 and 500 cm-1. Spectroscopic evidence for the formation of a hydrogen bonded complex has been found and the complexation enthalpy Delta(LXe)H degrees in the temperature interval between 173 and 215 K, was determined to be 14.4 (7) kJ mol-1. The parallel fundamentals nu1 and nu2 of ammonia reveal a strong narrowing effect upon complex formation, whereas the perpendicular fundamentals nu3 and nu4 show a modest decrease of their width. CP corrected ab initio calculations at the MP2(FULL)/6-311++G(3df,2pd) level predict a linear geometry for the complex, characterized by a small red shift of the CH stretch frequency of fluoroform. The ab initio interaction energy was found to be compatible with the isolated molecule complexation energy extrapolated from the experimental Delta(LXe)H degrees .     

Time-resolved fluorescence of the bacteriophage T4 capsid protein gp23

The time-resolved fluorescence properties of the bacteriophage T4 capsid protein gp23 are investigated. The structural characteristics of this protein are largely unknown and can be probed by recording time-resolved and decay-associated fluorescence spectra and intensity decay curves using a 200 ps-gated intensified CCD-camera. Spectral and decay data are recorded simultaneously, which makes data acquisition fast compared to time-correlated single-photon counting. A red-shift of the emission maximum within the first nanosecond of decay is observed, which can be explained by the different decay-associated spectra of fluorescence lifetimes of the protein in combination with dipolar relaxation. In addition, iodide quenching experiments are performed, to study the degree of exposure of the various tryptophan residues. A model for the origin of the observed lifetimes of 0.032 +/- 0.003, 0.39 +/- 0.06, 2.1 +/- 0.1 and 6.8 +/- 0.8 ns is presented: the 32 ps lifetime can be assigned to the emission of a buried tryptophan residue, the 0.4 and 2.1 ns lifetimes to two partly buried residues, and the 6.8 ns lifetime to a single tryptophan outside the bulk of the folded gp23.     

Molecular gradients: an efficient approach for optimizing the surface properties of biomaterials and biochips

A variety of molecular gradients of alkanethiols with the structure HS-(CH(2))(m)-X (m = 15; X = COOH, CH(2)NH(2), or CH(3)) and oligo(ethylene glycol)-terminated alkanethiols with the structures HS-(CH(2))(15)-CO-NH-Eg(n) (n = 2, 4, or 6), HS-(CH(2))(15)-CO-NH-Eg(2)-(CH(2))(2)-NH-CO-(CH(2))(4)-biotin, and HS-(CH(2))(15)-CO-NH-Eg(6)-CH(2)-COOH were prepared on polycrystalline gold films. These gradients were designed to serve as model surfaces for fundamental studies of protein adsorption and immobilization phenomena. Ellipsometry, infrared spectroscopy, and X-ray photoelectron spectroscopy, operating in scanning mode, were used to monitor the layer composition, gradient profiles, tail group conformation, and overall structural quality of the gradient assemblies. The gradient profiles were found to be 4-10 mm wide, and they increased in width with increasing difference in molecular complexity between the thiols used to form the gradient. The oligo(ethylene glycol) thiols are particularly interesting because they can be used to prepare so-called conformational gradients, that is, gradients that display a variation in oligo(ethylene glycol) chain conformation from all trans on the extreme Eg(2,4) sides, via an amorphous-like phase in the mixing regimes, to helical at the extreme Eg(6) sides. We demonstrate herein a series of experiments where the above gradients are used to evaluate nonspecific binding of the plasma protein fibrinogen, and in agreement with previous studies, the highest amounts of nonspecifically bound fibrinogen were observed on all-trans monolayers, that is, on the extreme Eg(2,4) sides. Moreover, gradients between Eg(2) and a biotinylated analogue have been prepared to optimize the conditions for the immobilization of streptavidin. Ellipsometry and infrared spectroscopy reveal high levels of immobilization over a fairly broad range of compositions in the gradient regime, with a maximum between 50 and 60% of the biotinylated analogue in the monolayer. A pI gradient composed of (NH(3)(+)/COO(-))-terminated thiols was also prepared and evaluated with respect to its ability to separate differently charged proteins, pepsin, and lysozyme, on a solid surface.     

Synthesis and properties of phenyl benzoate-based and biphenyl-based liquid crystalline thiol-ene monomers

Novel phenyl benzoate-based and biphenyl-based liquid crystalline thiol-ene monomers were synthesized and their properties investigated. By varying the bridging unit and spacer length, the type of mesophase can be tuned from the low ordered nematic and smectic A phase in the case of the phenyl benzoate-based monomers, to the highly ordered crystal E phase for the biphenyl-based monomers and their corresponding bromo precursors. We investigated the degree of order of the phenyl benzoate-based materials using the Haller method. Possible premature polymerization of these monomers was examined by size exclusion chromatography. The materials exhibit low transition temperatures and a high stability at typical handling times and temperatures. Consequently, these monomers are useful for in situ polymerization with anisotropic inert solvents, which could potentially lead to new architectures and enhanced electro-optical properties of devices. The use of the biphenyl-based monomers appears to be of limited use for polymerizations in anisotropic solution. However, as a result of their intrinsic high degree of molecular order, these monomers form a particularly interesting class of reactive materials that can be bulk polymerized to give main chain polymers with highly defined mechanical and optical or electro-optical properties.     

Preparation,Characterization and Electromagnetic Shielding Effectiveness of Conductive Polythiophene/Poly(ethylene terephthalate) Composite Fibers

Conductive polythiophene (PTh)/poly(ethylene terephthalate) (PET) composite fibers were prepared by polymerization of thiophene in the presence of PET fibers in acetonitrile medium using FeCl₃. The effects of polymerization conditions such as oxidant/monomer mol ratio and polymerization temperature and time on PTh content and surface electrical resistivity of PTh/PET composite fiber were investigated in detail. It was observed that the usage of preswelled PET fibers in dichloromethane increased the PTh content and decreased surface resistivity of composite fiber. Composite fiber having the highest PTh content (5.7%) and the lowest surface resistivity (80 kΩ) was obtained at 20°C with 1.25 M FeCl₃ and 0.42 M thiophene concentrations. The washing effects of laundering detergent and dry cleaning liquid on surface resistivity of composite fibers were investigated. The electromagnetic shielding effectiveness (EMSE) and relative shielding efficiency by absorption and reflection of composite fibers were measured in the radio and microwave frequency range. The results show that the EMSE values decreased with increasing frequency from radio waves to microwaves with an attenuation of 21 dB to 4 dB.     

Simultaneous serum desalting and total protein determination by macroporous reversed-phase chromatography

Macroporous reversed-phase (mRP) chromatography was successfully used to develop an accurate and precise method for total protein in serum. The limits of detection (0.83 μg, LOD) and quantification (2.51 μg, LOQ) for the mRP method are comparable with those of the widely used micro BCA protein assay. The mRP method can be used to determine the total protein concentration across a wide dynamic range by detecting chromatographic peaks at 215 nm and 280 nm. The method has the added advantage of desalting and denaturing proteins, leading to more complete digestion by trypsin and to better LC–MS–MS identification in shotgun proteomics experiments.