Adsorption of comb copolymers on weakly attractive solid surfaces

In this work continuum and lattice Monte Carlo simulation methods are used to study the adsorption of linear and comb polymers on flat surfaces. Selected polymer segments, located at the tips of the side chains in comb polymers or equally spaced along the linear polymers, are attracted to each other and to the surface via square-well potentials. The rest of the polymer segments are modeled as tangent hard spheres in the continuum model and as self-avoiding random walks in the lattice model. Results are presented in terms of segment-density profiles, distribution functions, and radii of gyration of the adsorbed polymers. At infinite dilution the presence of short side chains promotes the adsorption of polymers favoring both a decrease in the depletion-layer thickness and a spreading of the polymer molecule on the surface. The presence of long side chains favors the adsorption of polymers on the surface, but does not permit the spreading of the polymers. At finite concentration linear polymers and comb polymers with long side chains readily adsorb on the solid surface, while comb polymers with short side chains are unlikely to adsorb. The simple models of comb copolymers with short side chains used here show properties similar to those of associating polymers and of globular proteins in aqueous solutions, and can be used as a first approximation to investigate the mechanism of adsorption of proteins onto hydrophobic surfaces.     

A closed-loop logistics model for remanufacturing

Recoverable product environments are becoming an increasingly important segment of the overall push in industry towards environmentally conscious manufacturing. Integral to the recoverable product environment is the recoverable manufacturing system that focuses on recovering the product and extending its life through remanufacture or repair. Remanufacturing provides the customer with an opportunity to acquire a product that meets the original product standards at a lower price than a new product. The flow of materials and products in this environment occurs both from the customer to the remanufacturer (reverse flow), and from the remanufacturer to the customer (forward flow). Since most of the products and materials may be conserved, essentially this forms a closed-loop logistics system. We present a 0–1 mixed integer programming model that simultaneously solves for the location of remanufacturing/distribution facilities, the transshipment, production, and stocking of the optimal quantities of remanufactured products and cores. We also discuss the managerial uses of the model for logistics decision-making.     

Contributions of conformational compression and preferential transition state stabilization to the rate enhancement by chorismate mutase

The rate enhancement provided by the chorismate mutase (CM) enzyme for the Claisen rearrangement of chorismate to prephenate has been investigated by application of the concept of near attack conformations (NACs). Using a combined QM/MM Monte Carlo/free-energy perturbation (MC/FEP) method, 82% and 100% of chorismate conformers were found to be NAC structures in water and in the CM active site, respectively. Consequently, the conversion of non-NACs to NACs does not contribute to the free energy of activation from preorganization of the substrate into NACs. The FEP calculations yielded differences in free energies of activation that well reproduce the experimental data. Additional calculations indicate that the rate enhancement by CM over the aqueous phase results primarily from conformational compression of NACs by the enzyme and that this process is enthalpically controlled. This suggests that preferential stabilization of the transition state in the enzyme environment relative to water plays a secondary role in the catalysis by CM.     

Ion-exchange displacement chromatography of proteins Dextran-based polyelectrolytes as high affinity displacerss

Dextran-based polyelectrolyte displacers were successfully employed for the displacement purification of proteins in ion-exchange displacement systems. The effect of molecular mass was investigated by examining the efficacy of DEAE-dextran and dextran sulfate displacers of various molecular masses in cation- and anion-exchange systems, respectively. Induced salt gradients produced during these displacement experiments were measured in order to study their effect on the protein separations. The unique characteristics of these displacements were well predicted by simulations obtained from a steric mass action (SMA) ion-exchange model. These displacements differ from the traditional vision of displacement chromatography in several important ways: the isotherm of the displacer does not necessarily lie above the feed component isotherms; the concentration of the displaced proteins can sometimes exceed that of the displacer; higher-molecular-mass displacers are not necesarily more efficacious than lower-molecular-mass compounds; and the salt gradients induced by the adsorption of the displacer produce different salt micro-environments for each displaced protein.     

X-ray diffraction and Raman studies of the CuGeO3(III)-(IV) transformation under high pressures

Both X-ray diffraction and Raman spectroscopy measurement were carried out on the same powder sample of CuGeO(3)(III) in a diamond anvil cell to high pressures at room temperature. The phase transformation of (III)-(IV) phase was observed at about 7GPa with both methods and the results were also in accord with previous powder diffraction and Raman measurements, respectively. However, the powder diffraction data were strikingly different from those reported in a recent single-crystal study on the phase (III). It is, therefore, evident that the phase transformations in CuGeO(3)(III) would be as complicated as those in CuGeO(3)(I) and that the monoclinic phase obtained from single-crystal phase (III) at approximately 7GPa is not the phase (IV) previously observed but rather a new phase (IVa) in CuGeO(3).     

Estimation of electrochemical quartz crystal microbalance frequencies from cyclic voltammetric data:—underpotential deposition of metals as an illustration

The estimation of electrochemical quartz crystal microbalance (EQCM) frequencies from a given cyclic voltammetric data is analysed using underpotential deposition (UPD) of metals as an illustrative process. The crucial role played by the surface roughness of electrodes and electrosorption valency of the depositing species is pointed out. The computed EQCM frequency shifts for the UPD of Cd and Tl on polycrystalline Ag electrodes are in satisfactory agreement with the experimental data.

Synthesis,spectroscopic and crystal structure analysis of a compound with pharmocophoric substituent: 2-cyclohexyl-6-(2-oxo-2H-chromen-3-yl)- imidazo[2,1-b][1,3,4]thiadiazole-5-carbaldehyde

Imidazo[2,1-b][1,3,4] thiadiazole derivatives are significant for their various pharmacological properties. This paper reports the synthesis and structure of one of them, 2-cyclohexyl-6-(2-oxo-2H-chromen-3-yl)imidazo[2,1-b][1,3,4]thiadiazole-5-carbaldehyde. The compound crystallizes in the monoclinic space group P2₁/c with a=17.316(3)?, b=6.5420(9)?, c =17.056(3)?, β=112.909(2)°, V=1779.7(4)?³, z=4. The, Imidazo[2,1-b][1,3,4] thiadiazole and the coumarin ring systems are each planar but inclined at an angle of 48.14(2)° towards each other. The crystal structure is stabilized by C–H … O interactions.     

Diboramacrocycles: reversible borole dimerisation–dissociation systems

We report that the outcome of the tin–boron exchange reaction of a mixed thiophene-benzo-fused stannole with aryldibromoboranes is associated with the steric bulk of the aryl substituent of the borane reagent, leading to either boroles or large diboracycles as products. NMR spectroscopic studies indicate that the two products can reversibly interconvert in solution, and mechanistic density functional theory (DFT) calculations reveal boroles to be intermediates in the formation of the diboracyclic products. The addition of Lewis bases to the diboracycles leads to the corresponding borole adducts, demonstrating that they react as “masked” boroles. Additionally, the reaction of the title compounds with a series of organic azides affords complex heteropropellanes, formally 2 : 1 borole-azide adducts, that deviate from the usual BN aromatic compounds formed via nitrogen atom insertion into the boroles.

Diboramacrocycles are a new form of borole dimers, participating in various addition reactions as “masked” boroles. The reaction of a less crowded diboramacrocycle with organic azides affords unprecedented complex heteropropellanes.     

Designing pattern-recognition surfaces for selective adsorption of copolymer sequences using lattice monte carlo simulation

We describe a simulation method to design surfaces for recognizing specific monomer sequences in copolymers. We fix the monomer sequence statistics of the AB copolymers on a surface containing two types of sites and allow the simulation to iterate towards an optimal surface pattern that can recognize and selectively adsorb the sequence in the copolymer. During the simulation the surface pattern is designed by switching identities of two randomly picked sites. For copolymers with less blocky sequences the designed surfaces recognize the correct sequence well when the segment-surface interactions dominate over the intersegment interactions. For copolymers with more blocky sequences recognition is good when the segment-surface interactions are only slightly stronger than the intersegment interactions.     

Bicyclo[1.1.0]butadiene (trialene): An experimentally viable molecule?

Molecular orbital calculations on the C₄H₂ potential energy surface indicate singlet trialene (1) not only to be thermodynamically unstable, but also to have negligible barriers to interconversion to diacetylene.