Reversible protein adsorption and bioadhesion on monolayers terminated with mixtures of oligo(ethylene glycol) and methyl groups

Surface-grafted, environmentally responsive polymers have shown great promise for controlling adsorption and desorption of macromolecules and cells on solid surfaces. In the paper, we demonstrate that certain mixed self-assembled monolayers (SAMs) of oligo(ethylene glycol) (OEG) and methyl-terminated alkanethiolates on gold form surfaces with switchable hydrophobicity and tendency for protein adsorption and cellular attachment. At temperatures above 32 degrees C, SAMs with a surface density of approximately 50% OEG adsorbed significant amounts of pyruvate kinase and lysozyme, whereas below this temperature, these same SAMs were resistant to the adsorption of these proteins. Furthermore, protein layers adsorbed to these SAMs above 32 degrees C were removed upon rinsing with water below this temperature. Similar results were seen for attachment and release of the marine bacterium, Cobetia marina. The change from nonresistance to adsorptive state of the SAMs was concomitant with a change in advancing water contact angle. Vibrational sum frequency generation spectroscopy suggests that the temperature-induced changes coincide with a disorder-to-partial order transition of the hydrated methylene chains of the OEG moieties within the SAMs. Mixed OEG-methyl SAMs represent both a convenient means of controlling macromolecular and cellular adsorption within the laboratory and a useful tool for relating adsorption properties to molecular structures within the SAMs.     

Synthesis and chelation properties of new polymeric ligand derived from 8-hydroxy-5-azoquinoline hydroxy benzene

8-Hydroxy-5-azoquinoline phenyl methacrylate-formaldehyde (8H5AQPMA-F) macromonomer was prepared from methacryloyl chloride with condensation products of 8-hydroxy-5-azoquinoline phenol-formaldehyde, and polymerized in DMF at 70 °C using benzoyl peroxide as free radical initiator. Poly(8H5AQPMA-F) was characterized by infrared and nuclear magnetic resonance spectroscopic techniques. Polychelates were obtained when the DMF solution of the resin containing few drops of ammonia was treated with the aqueous solution of Cu(II)/Ni(II). Elemental analysis of the polychelates indicates that the metal to ligand ratio was about 1:2. The IR spectra of polychelates suggest that the metals were coordinated through the oxygen of the phenolic-OH group and nitrogen of the quinoline ligand. The DRS and magnetic moment data indicate a square planar for Cu(II) complex whereas octahedral for Ni(II) complex. The TGA data revealed the thermal stability of the resin and the polychelates. X-ray diffraction study revealed the incorporation of the metal ions significantly enhanced the degree of crystallinity. The sorption properties of the chelate-forming resin towards various divalent metal ions [Cu(II) and Ni(II)] were studied as a function of pH and electrolyte.     

Universal consequences of the presence of excluded volume interactions in dilute polymer solutions undergoing shear flow

The role of solvent quality in determining the universal material properties of dilute polymer solutions undergoing steady simple shear flow is examined. A bead-spring chain representation of the polymer molecule is used, and the influence of solvent molecules on polymer conformations is modelled by a narrow Gaussian excluded volume potential that acts pairwise between the beads of the chain. Brownian dynamics simulations data, acquired for chains of finite length, and extrapolated to the limit of infinite chain length, are shown to be model independent. This feature of the narrow Gaussian potential, which leads to results identical to a delta-function repulsive potential, enables the prediction of both universal crossover scaling functions and asymptotic behavior in the excluded volume limit. Universal viscometric functions, obtained by this procedure, are found to exhibit increased shear thinning with increasing solvent quality. In the excluded volume limit, they are found to obey power law scaling with the characteristic shear rate beta, in close agreement with previously obtained renormalization group results. The presence of excluded volume interactions is also shown to lead to a weakening of the alignment of the polymer chain with the flow direction.     

The effects of axial ligands on electron distribution and spin states in iron complexes of octaethyloxophlorin, intermediates in heme degradation

The results presented here show that the nature of the axial ligand can alter the distribution of electrons between the metal and the porphyrin in complexes where there is an oxygen atom replacing one of the meso protons. The complexes (1-MeIm)(2)Fe(III)(OEPO) and (2,6-xylylNC)(2)Fe(II)(OEPO(*)) (where OEPO is the trianionic octaethyloxophlorin ligand and OEPO(*) is the dianionic octaethyloxophlorin radical) were prepared by addition of an excess of the appropriate axial ligand to a slurry of [Fe(III)(OEPO)](2) in chloroform under anaerobic conditions. The magnetic moment of (2,6-xylylNC)(2)Fe(II)(OEPO(*)) is temperature invariant and consistent with a simple S = (1)/(2) ground state. This complex with an EPR resonance at g = 2.004 may be considered as a model for the free-radical like EPR signal seen when the meso-hydroxylated heme/heme oxygenase complex is treated with carbon monoxide. In contrast, the magnetic moment of (1-MeIm)(2)Fe(III)(OEPO) drops with temperature and indicates a spin-state change from an S = (5)/(2) or an admixed S = (3)/(2),(5)/(2) state at high temperatures (near room temperature) to an S = (1)/(2) state at temperatures below 100 K. X-ray diffraction studies show that each complex crystallizes in centrosymmetric form with the expected six-coordinate geometry. The structure of (1-MeIm)(2)Fe(III)(OEPO) has been determined at 90, 129, and 296 K and shows a gradual and selective lengthening of the Fe-N(axial bond). This behavior is consistent with population of a higher spin state at elevated temperatures.     

Tandem radical reactions and ring-closing metathesis. Application in the synthesis of cyclooctenes

[reaction: see text] Fumarate- and acrylate-substituted oxazolidinones undergo tandem radical reaction to form dienes in moderate to good yields. The resulting dienes provide cyclooctenes in moderate to good yields after ring-closing metathesis (RCM). The role of the carbon backbone substituents and other variables in the efficiency of the eight-membered ring formation is discussed.     

An approximate max-flow min-cut relation for undirected multicommodity flow,with applications

In this paper, we prove the first approximate max-flow min-cut theorem for undirected multicommodity flow. We show that for a feasible flow to exist in a multicommodity problem, it is sufficient that every cut's capacity exceeds its demand by a factor ofO(logClogD), whereC is the sum of all finite capacities andD is the sum of demands. Moreover, our theorem yields an algorithm for finding a cut that is approximately minimumrelative to the flow that must cross it. We use this result to obtain an approximation algorithm for T. C. Hu's generalization of the multiway-cut problem. This algorithm can in turn be applied to obtain approximation algorithms for minimum deletion of clauses of a 2-CNF formula, via minimization, and other problems. We also generalize the theorem to hypergraph networks; using this generalization, we can handle CNF clauses with an arbitrary number of literals per clause.Most of the results in this paper were presented in preliminary form in Approximation through multicommodity flow,Proceedings, 31th Annual Symposium on Foundations of Computer Science (1990), pp. 726–737.Research supported by the National Science Foundation under NSF grant CDA 8722809, by the Office of Naval and the Defense Advanced Research Projects Agency under contract N00014-83-K-0146, and ARPA Order No. 6320, Amendament 1.Research supported by NSF grant CCR-9012357 and by an NSF Presidential Young Investigator Award.     

On pathwise behavior of multiserver queues

In this paper, by exploiting recent results on the pathwise behavior of the workload process in single server, work conserving queues of theG/G/1/ type, we show that the workload of multiserver, work conserving queues ofG/G/m/ (m<) (andG/G/) queues satisfies an o(t) growth condition, provided that the time average of the work brought into the system is less thanm form < (and finite form=).     

Local magnetism of Rh in Ni-Rh alloys near the critical composition for ferromagnetism

Local magnetic behaviour of Rh implanted into Ni-Rh alloys near the critical Rh compositionx=0.37 has been studied using the TDPAC method. The observed Curie-Weiss type local susceptibility reflects the presence of large d spin polarization around Rh yielding a total moment of 4.7 _B. Our results show that the magnetism of Rh in the alloys depends strongly on the number of Ni near neighbour atoms.