Reversed-phase poly(styrene-divinylbenzene) materials optimised for large scale preparative and process purification of synthetic peptides and recombinant proteins

Rigid macroporous copolymers of styrene and divinylbenzene have been designed for large-scale preparative and process-scale purification of synthetic peptides and recombinant proteins. The polymeric particles are mechanically stable and hence able to operate at the required high linear velocities. The pore size and pore morphology has been optimised to enable unhindered solute diffusion whilst providing maximum available surface area to enhance loading capacity. A 100 A pore size has been developed for synthetic peptides and a 300 A pore size for recombinant proteins. Precise control of particle size, within the range 10 to 20 microm, is possible which together with the very narrow particle size distribution enables maximum resolution/loading to be obtained within the pressure limits of the instrumentation being used. The chemical stability of the polymer enables cleaning in place with 1 M sodium hydroxide without particle dissolution or a deterioration in selectivity. These materials can be packed into compression hardware and are manufactured as single lots up to 100 kg (300 l) batch size.     

A dithienylethene-tethered beta-cyclodextrin dimer as a photoswitchable host

The binding of TSPP by a dithienylethene-tethered beta-cyclodextrin dimer can be altered reversibly by irradiation with light.     

Structure and ion exchange properties of a new cobalt borate with a tunnel structure "templated" by Na+

The new anhydrous borate Na2Co2B12O21 has been synthesized by flux methods and studied by single-crystal X-ray diffraction (space group I2/a with a = 17.1447(15) A, b = 4.5530(5) A, c = 19.4408(15) A, beta = 103.212(5) degrees , V = 1477.4(2) A3, Z = 4). Refinement of its structure reveals it is the first metaborate exhibiting a tunnel network, with internal dimensions of 4.5 x 8.8 A2. Further single-crystal diffraction studies show that the Na+ ions within the tunnels are exchangeable with Li+ along with the absorption of water molecules to form Li2(H2O)2Co2B12O21, making this compound a unique non-siliceous zeotype.     

On automorphisms of the degrees that preserve jumps

IfF is an automorphism of the degrees of unsolvability that preserves the jump operator, thenF leaves fixed all the degreesc that satisfyc≧0 ⁽³⁾. The results of this paper were part of the author’s PhD thesis (Illinois 1977), supervised by Carl G. Jockusch, Jr.     

Contactless gating,surface charging and illumination effects in a buried Al<Subscript>0.24</Subscript>Ga<Subscript>0.76</Subscript>As/GaAs quantum well structure

The conductivity of an Al_0.24Ga_0.76As/GaAs quantum well was studied as a function of the surface charge generated by electron bombardment of the sample in the absence of an externally applied surface electric field. Under a suitable rate of electron irradiation, it was possible to completely shut off the conductive channel, implying a surface density . Light illumination quenches the increase of the resistivity, apparently due to photoemission from the metastable surface states. Upon turning off the electron bombardment the surface charge on adsorbed layers of xenon and water at 8 K decays in room temperature darkness with a lifetime τ= 0.30 ±0.02 s. The average charging efficiency, is μ₀ ≃0.001. Surface charging is shown to be an effective method for contactless gating of field effect devices.     

Microtubule structure and its stabilisation

Microtubules are designed to be dynamically unstable. GTP hydrolysis converts an initially stable polymeric structure into an unstable one in which strain at the interfaces between longitudinal neighbours in the helical lattice of subunits is balanced by lateral interactions. However, stability can be modulated by a variety of factors, including associated proteins and a variety of drug molecules. Stabilising drugs such as Taxol and the assembly-promoting repeat motifs of tau protein occupy a special pocket in beta-tubulin. Microtubule destabilizing drugs such as colchicine alter the longitudinal interfaces of the subunits so that they cannot assemble into a microtubule lattice. These mechanisms are discussed in terms of the atomic structure of the protein.     

Local optical properties, electron densities, and london dispersion energies of atomically structured grain boundaries

Quantitative analysis of spatially resolved valence electron energy-loss spectra shows strong physical property contrasts for Sigma5 and near Sigma13 grain boundaries in Fe-doped SrTiO3, resulting in London dispersion interaction energies of 14 to 50 mJ/m(2) between the adjacent grains. The determination of local physical properties of grain boundary cores and the appreciable contribution of long-range London dispersion to interface energies provides new information on formation and control of interfaces in materials.     

Selectivity of quadruplex DNA stationary phases toward amino acids in homodipeptides and alanyl dipeptides

Series of dipeptides, including homodipeptides and alanyl dipeptides, were separated using quadruplex (G-quartet) DNA stationary phases in open-tubular capillary electrochromatography (OTCEC). The stationary phases were constructed by covalently attaching the DNA oligonucleotides to the inner capillary surface. Three different G-quartet forming oligonucleotides were investigated: the two-plane G-quartet forming thrombin-binding aptamer, the four-plane analogue of the thrombin-binding aptamer, and a two-plane oligonucleotide identical to the thrombin-binding aptamer except for the replacement of the guanine by thymine in the central bridging loop of the G-quartet structure. Results were compared with results obtained using capillary electrophoresis on a bare capillary and OTCEC using an oligonucleotide with the same base composition as the thrombin-binding aptamer but in a different sequence that does not allow G-quartet formation as the stationary phase.     

Photochemical pinacol rearrangements of unsymmetrical diols

The photochemical pinacol reaction of a series of nonsymmetrical 9-fluorenyl-substituted vic-diols was investigated and compared with their acid-catalyzed thermal reaction. Unlike the thermal reaction, the radiation-induced processes involve only fluorenyl cations, as is reflected in differences of product distribution between the two reactions. From the product studies, substituent migratory aptitudes are reversed in the photochemical process, suggesting that kinetic control takes place under neutral conditions unlike the acid-catalyzed thermal reactions. The presence of fluorenyl cation intermediates and their lifetimes were established by laser flash spectroscopy studies.