Hydrophobic interaction chromatography of proteins. III. Unfolding of proteins upon adsorption

Hydrophobic interaction chromatography (HIC) exploits the hydrophobic properties of protein surfaces for separation and purification by performing interactions with chromatographic sorbents of hydrophobic nature. In contrast to reversed-phase chromatography, this methodology is less detrimental to the protein and is therefore more commonly used in industrial scale as well as in bench scale when the conformational integrity of the protein is important. Hydrophobic interactions are promoted by salt and thus proteins are retained in presence of a cosmotropic salt. When proteins are injected on HIC columns with increasing salt concentrations under isocratic conditions only, a fraction of the applied amount is eluted. The higher the salt concentration, the lower is the amount of eluted protein. The rest can be desorbed with a buffer of low salt concentration or water. It has been proposed that the stronger retained protein fraction has partially changed the conformation upon adsorption. This has been also corroborated by physicochemical measurements. The retention data of 5 different model proteins and 10 different stationary phases were evaluated. Partial unfolding of proteins upon adsorption on surfaces of HIC media were assumed and a model describing the adsorption of native and partial unfolded fraction was developed. Furthermore, we hypothesize that the surface acts as catalyst for partial unfolding, since the fraction of partial unfolded protein is increasing with length of the alkyl chain.     

Edge-compression fixture for buckling studies of corrugated board panels

A test fixture, developed for evaluating the preand postbuckling response of simply supported, nearly flat, rectangular corrugated board panels subjected to edge compression is evaluated. The test fixture enables loading of panels into the postbuckling regime until collapse. The shadowmoiré method verified that buckling in the first mode occurred, and that there was symmetry of the adge-boundary conditions. Through an iterative regression model, experimental curves of load versus out-of-plane displacement for isotropic panels were fitted to an equation governing the nonlinear postbuckling response. This method provides the critical buckling load, a postbuckling parameter and the amplitude of initial imperfection of the panel. Comparison with analytical results revealed that simply supported boundary conditions were closely achieved. Examination of compressively loaded corrugated board panels showed that collapse occurred due to compressive failures of the facings in the highly stressed edge regions without severe influence from stress concentrations at load introduction and edge supports.     

Grafting Dendrons onto Pillar[5]Arene Scaffolds

With their ten peripheral substituents, pillar[5]arenes are attractive compact scaffolds for the construction of nanomaterials with a controlled number of functional groups distributed around the macrocyclic core. This review paper is focused on the functionalization of pillar[5]arene derivatives with small dendrons to generate dendrimer-like nanomaterials and bioactive compounds. Examples include non-viral gene vectors, bioactive glycoclusters, and liquid-crystalline materials.     

Capillary electrochromatography and preconcentration of neutral compounds on poly(dimethylsiloxane) microchips

Capillary electrochromatography (CEC) and preconcentration of neutral compounds have been realized on poly(dimethylsiloxane) (PDMS) microchips. The channels are coated with polyelectrolyte multilayers to avoid absorption of hydrophobic analytes into PDMS. The structures of a microchip include an injector and a bead chamber with integrated frits, where the particles of the stationary phase are completely retained. Dimensions of the frit structures are 25 micro mx20 micro m, and the space between the structures is 3 micro m. A neutral compound, BODIPY, that is strongly absorbed into native PDMS, is successfully and selectively retained on octadecylsilane-coated silica beads in the bead chamber with a concentration enhancement of up to 100 times and eluted with elution buffer solution containing 70% acetonitrile. Preconcentrations and CEC separations of coumarins have been conducted with the same device and achieved complete separations in less than 50 s.     

Cluster expansion models for flexible‐backbone protein energetics

Protein structure prediction and design often involve discrete modeling of side‐chain conformations on structural templates. Introducing backbone flexibility into such models has proven important in many different applications. Backbone flexibility improves model accuracy and provides access to larger sequence spaces in computational design, although at a cost in complexity and time. Here, we show that the influence of backbone flexibility on protein conformational energetics can be treated implicitly, at the level of sequence, using the technique of cluster expansion. Cluster expansion provides a way to convert structure‐based energies into functions of sequence alone. It leads to dramatic speed‐ups in energy evaluation and provides a convenient functional form for the analysis and optimization of sequence‐structure relationships. We show that it can be applied effectively to flexible‐backbone structural models using four proteins: α‐helical coiled‐coil dimers and trimers, zinc fingers, and Bcl‐x_L/peptide complexes. For each of these, low errors for the sequence‐based models when compared with structure‐based evaluations show that this new way of treating backbone flexibility has considerable promise, particularly for protein design. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Rapid treatment of CIGS particles by intense pulsed light

Intense pulsed light (IPL) technique has been proposed to make large grains Cu(In_0.7Ga_0.3)Se₂ (CIGS) film using CIGS particles. The proposed process is non-vacuum based and performed at room temperature without selenization treatment. Melting and recrystallization of CIGS particles to larger grains without structural deformation and phase transformation are proved with adequate characterization evidences. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion analysis (EDS) were used to characterize the prepared films. Melting of the CIGS particles and recrystallization to larger grains by light energy in 20 ms short reaction time could be the reason for no structural deformation and secondary phase generation during the process. The CIGS film prepared from its constituent nanoparticles by IPL treatment has great potential for use as absorber layer for solar cell application and is expected to have large impact on cell fabrication process in terms of cost reduction and simplified processing.     

Template Synthesis of Three‐Dimensional Hexakisimidazolium Cages

A procedure for the synthesis of three‐dimensional hexakisimidazolium cage compounds has been developed. The reaction of the trigonal trisimidazolium salts H₃L(PF₆)₃, decorated with three N‐olefinic pendants, and silver oxide yielded trinuclear trisilver(I) hexacarbene molecular cylinders of the type [Ag₃L₂]³⁺ with the olefinic pendants from the two different tricarbene ligands arranged in three pairs. Subsequent UV irradiation gave three cyclobutane links between the two tris‐NHC ligands in three [2+2] cycloaddition reactions, thereby generating a three‐dimensional hexakis‐NHC ligand. Removal of the metal ions resulted in the formation of three‐dimensional hexakisimidazolium cages with a large internal cavity.     

Teh Bloch space of M-harmonic functions on bounded symmetric domains

New characterizations of Bloch functions on a bounded symmetric domain in ⁿ are given in terms of the intrinsic metrics. Various criteria for an M-harmonic function to be Bloch or little Bloch are obtained. These criteria establish the links between the M-harmonic Bloch and little Bloch functionsf and other notions including the Laplace-Betrami operator. We also study some basic properties of M-harmonic Bloch and little Bloch functions, extending previously known results for holomorphic functions. The space of M-harmonic functions contains the Poisson integrals of Borel measures and all pluriharmonic functions.