PubMed Health⌕ Search

Biomedical subjects

Kevin E Van Cott

Publications and source records attributed to Kevin E Van Cott.

7 recordsLinked to original sources
PubMed2006

Efficient, thermally stable, second order nonlinear optical response in organic hybrid covalent/ionic self-assembled films.

A covalent/electrostatic layer-by-layer self-assembly method was used to achieve polar ordering of a water soluble, reactive dye in the fabrication of nonlinear optical (NLO) films. We observed a quadratic relationship between the second harmonic intensity I2(omega) and bilayer number for all films made with Procion Brown MX-GRN, demonstrating that the polar ordering of the chromophores is consistent in each successive bilayer. As the ionic strength of the dye deposition solution was increased to 0.5 M NaCl, the of the films increased by approximately 250% to 50 x 10(-9) esu, with a corresponding average chromophore tilt angle of 38 degrees . This was attributed to increased shielding of the dye charges which led to higher chromophore density in the bilayers. The electrooptic coefficient for films of 50 bilayers fabricated at 0.5 M NaCl was 14 +/- 2 pm/V. Importantly, these films exhibited excellent thermal stability, with only a 10% decrease in (I2(omega))(1/2) after 36 h at 85 degrees C and then 24 h at 150 degrees C. Furthermore, the (I2(omega))(1/2) recovered completely upon cooling to room temperature. These results with a commodity textile dye point to the potential value of this class of reactive chromophores and this self-assembly method for fabrication of electrooptic materials at ambient conditions from aqueous solutions.

Journal Article↗
PubMed2005

Unnatural proteins for the control of surface forces.

We introduce a new method for the stabilization of colloidal particles via the synthesis and adsorption of unnatural proteins. Biosynthesis of protein-based polymers offers the advantages of preparation of complex sequences through control of the primary sequence, monodisperse polymers, ease of combinatorial search for anchor blocks, environmentally friendly synthesis, use of water as the solvent, and incorporation of a palette of known natural proteins. We have synthesized an unnatural protein with the sequence thioredoxin-Pro(39)Glu(10) for modification of the forces between alumina particles. The polyglutamate sequence, Glu(10), is anionic (pH > 3) and is designed to anchor the protein to positively charged solids, e.g. alumina in water (pH < 9). The polyproline sequence, Pro(39), is neutral. The thioredoxin is a recombinant form of the natural globular protein with a histidine patch (His-patch-thioredoxin) and is zwitterionic. The combined thioredoxin-Pro(39) sequence is hydrophilic with pI approximately 6.3. This block is designed to remain in solution, thereby providing a steric barrier to the approach of two particles in a range of salt and pH conditions. Ellipsometry experiments show that thioredoxin-Pro(39)Glu(10) does adsorb to alumina. Force measurements with the atomic force microscopy (AFM) colloid probe technique show that adsorption of thioredoxin-Pro(39)Glu(10) leads to repulsive forces that decay exponentially with the separation between the surfaces and are independent of salt concentration in the range 0.001-0.1 M KNO(3). This demonstrates that the repulsive forces are not electrostatic. We hypothesize that the repulsion is due to confinement and loss of solvent for the adsorbed polymer; the forces are similar to those expected for a polymer brush. Force measurements between thioredoxin-coated alumina surfaces also show a repulsive force, but the force has a decay length that is consistent with electrostatic double-layer forces: the thioredoxin has not neutralized the surface charge of the underlying alumina. Our results point to interesting future experiments where recombinant DNA technology could be used to synthesize fusion proteins containing useful natural proteins and an anchor. This may allow preparation, via single-step aqueous self-assembly, of anchored proteins that maintain their natural structure. Our technique is not limited to homopolymer blocks; more complex primary sequences can be used.

Aluminum Oxide↗
PubMed2004

Purification of recombinant DNA-derived factor IX produced in transgenic pig milk and fractionation of active and inactive subpopulations.

Transgenic animal bioreactors can be engineered to make gram per liter quantities of complex recombinant glycoproteins in milk. However, little is known about the limitations in post-translational processing that occurs for very complex proteins and how this impacts the task of purification. We report on the purification of recombinant factor IX (rFIX) from the milk of transgenic pigs having an expression level of 2-3 g rFIX/(l(-1) h(-1)), an expression level that is about 20-fold higher than previously reported. This purification process efficiently recovers highly active rFIX and shows that even complex mixtures like pig milk, which contains 60 g/l total endogenous milk protein and multiple subpopulations of rFIX, can be processed using conventional, non-immunoaffinity chromatographic methods. Without prior removal of caseins, heparin-affinity chromatography was used to first purify the total population of rFIX at greater than 90% yield. After the total population was isolated, the biologically active and inactive subpopulations were fractionated by high-resolution anion exchange chromatography using an ammonium acetate elution. Capillary isoelectric focusing of the active and inactive rFIX fractions demonstrated that the active subpopulations are the most acidic.

Amino Acid Sequence↗
PubMed2004

Peak compression and resolution for electrophoretic separations in diverging microchannels.

We report the results of experiments and simulations on electrokinetic flow in diverging microchannels (with cross-sectional area that increases with distance along the channel). Because of conservation of mass and charge, the velocity of an analyte in the channel decreases as the channel cross-section increases. Consequently, the leading edge of a band of sample moves more slowly than the trailing edge and the sample band is compressed. Sample peak widths, rather than increasing diffusively with time, can then be controlled by the geometry of the channel and can even be made to decrease with time. We consider the possibility of using this peak compression effect to improve the resolution of electrophoretic separations. Our results indicate that for typical separations that are dispersion limited, this peak compression effect is more than offset by the decreased distance between peaks, and the separation resolution in diverging channels is worse than that found for straight channels at the same applied voltage. For separations in very short channels or at very high field strengths, however, when the separation efficiency is injection limited, the peak compression effect is dominant and diverging channels can then be used to achieve improved separation resolution.

Electrophoresis, Microchip↗
PubMedDate not supplied

Cloning strategy for producing brush-forming protein-based polymers.

Brush-forming polymers are being used in a variety of applications, and by using recombinant DNA technology, there exists the potential to produce protein-based polymers that incorporate unique structures and functions in these brush layers. Despite this potential, production of protein-based brush-forming polymers is not routinely performed. For the design and production of new protein-based polymers with optimal brush-forming properties, it would be desirable to have a cloning strategy that allows an iterative approach wherein the protein based-polymer product can be produced and evaluated, and then if necessary, it can be sequentially modified in a controlled manner to obtain optimal surface density and brush extension. In this work, we report on the development of a cloning strategy intended for the production of protein-based brush-forming polymers. This strategy is based on the assembly of modules of DNA that encode for blocks of protein-based polymers into a commercially available expression vector; there is no need for custom-modified vectors and no need for intermediate cloning vectors. Additionally, because the design of new protein-based biopolymers can be an iterative process, our method enables sequential modification of a protein-based polymer product. With at least 21 bacterial expression vectors and 11 yeast expression vectors compatible with this strategy, there are a number of options available for production of protein-based polymers. It is our intent that this strategy will aid in advancing the production of protein-based brush-forming polymers.

Amino Acid Sequence↗