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Highly branched poly(N-isopropyl acrylamide)s with peptide-end groups form colloidally stable dispersions of sub-micron particles above the lower critical solution temperature.

International audience; Small-angle neutron scattering (SANS) and neutron spin-echo (NSE) have been used to investigate the temperature-dependent solution behaviour of highly-branched poly(N-isopropylacrylamide) (HB-PNIPAM). SANS experiments have shown that water is a good solvent for both HB-PNIPAM and a linear PNIPAM control at low temperatures where the small angle scattering is described by a single correlation length model. Increasing the temperature leads to a gradual collapse of HB-PNIPAM until above the lower critical solution temperature (LCST), at which point aggregation occurs, forming disperse spherical particles of up to 60 nm in diameter, independent of the degree of branching. However, SANS from linear PNIPAM above the LCST is described by a model that combines particulate structure and a contribution from solvated chains. NSE was used to study the internal and translational solution dynamics of HB-PNIPAM chains below the LCST. Internal HB-PNIPAM dynamics is described well by the Rouse model for non-entangled chains.

The nanoscopic adhesive and frictional behaviour of end-grafted poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA) films (brushes) in contact with gold- or PDMAEMA-coated atomic force microscope tips in potassium halide solutions with different concentrations up to 300 mM is a strong function of salt concentration. The conformation of the polymers in the brush layer is sensitive to salt concentration, which leads to large changes in adhesive forces and the contact mechanics at the tip–sample contact, with swollen brushes (which occur at low salt concentrations) yielding large areas of contact and friction–load plots that fit JKR behaviour, while collapsed brushes (which occur at high salt concentrations) yield sliding dominated by ploughing, with conformations in between fitting DMT mechanics. The relative effect of the different anions follows the Hofmeister series, with I− collapsing the brushes more than Br− and Cl− for the same salt concentration.

A series of NIPAM/4-vinyl benzyl chloride copolymers were substituted with 4(5)-imidazole dithioic acid or N-pyrrole dithioic acid to form multi-functional linear dithioate-functional polymers, which can be used as macromolecular transfer agents in a controlled radical polymerisation (RAFT) process. The presence of imidazole dithioate or N-pyrrole dithioate units along the NIPAM copolymer was determined by (1)H NMR, which showed broad CH-imidazole or CH-N-pyrrole resonances. Subsequent reaction of these multi-branch point polymers to produce graft polymers was achieved by reaction with NIPAM in the presence of AIBN. The graft polymers are produced as mixtures containing the desired product and linear polymer. The linear polymer is produced following transfer to the pendant dithioate group. Some of the branched polymers formed from the imidazole dithioate polymers were insoluble in water whilst others were found to be water soluble only in the presence of copper(II) ions. The use of N-pyrrole dithioate groups was found to substantially increase the solubility of the branched polymers in conventional solvents.

Highly branched poly(NIPAM) have been prepared using the technique of reversible addition-fragmentation chain transfer (RAFT) polymerisation using a chain transfer agent that allows the incorporation of imidazole functionality in the polymer chain-ends. The lower critical solution temperature (LCST) of the polymers can be controlled by the amount of hydrophobe and GMA incorporated during copolymerisation procedures. These thermally responsive "smart" polymers were used to purify a His-tagged BRCA-1 protein fragment by affinity precipitation. [Diagram: see text]

Highly branched poly(N-isopropylacrylamide) (PNIPAM) compounds were prepared by copolymerization of 3H-imidazole-4-carbodithioic acid 4-vinylbenzyl ester, 1, with N-isopropylacrylamide (NIPAM) using reversible addition−fragmentation chain transfer (RAFT) polymerization. The polymerizations proceeded well with few side reactions. An increase in the content of 1 in the monomer feed appears to increase the number of branch chains, and at the same time no evidence was obtained for the presence of substituted acrylamide chain ends that may potentially result via elimination of the dithioate group. The polymer products show a clear tendency to increased molecular weight as the extent of conversion of monomer increases, while size exclusion chromatography (SEC) profiles indicate a complex distribution of molecular weights compared to linear polymers obtained with a non-RAFT carboxylate monomer. Both NMR and viscometry indicate that, as expected, increasing the amount of 1 in the feed has the effect of increasing...

Core–shell molecularly imprinted polymers (CS-MIPs) have been prepared by aqueous emulsion polymerization using water-soluble template molecules. An amphiphilic binding monomer, oleyl phenyl hydrogen phosphate and ethylene glycol dimethacrylate were used in the formation of highly crosslinked surfaces around divinyl benzene crosslinked polystyrene core colloids. Evidence was obtained by transmission electron microscopy (TEM) for a change in surface morphology when the polymer shell was formed in the presence of a template. The caffeine-imprinted polymers were shown to bind caffeine in preference to theophylline from an equimolar mixture of the compounds in aqueous solution at pH 7.0, whilst concentration–binding (Scatchard) curves revealed the presence of two populations of binding sites in aqueous phosphate buffer at pH 8.0 for caffeine and theophylline. Similar studies were also carried out for (S)-propranolol and (S)-atenolol at pH 5.5, which also revealed the presence of two populations of binding sites for core–shell particles imprinted with these compounds. (S)-Propranolol was selectively removed from a solution of (S)-propranolol and (S)-atenolol by both of the CS-MIPs, whereas the non-imprinted particle showed no selectivity for either component.

Poly(vinyl acetate) was prepared by radical polymerization with chain transfer to solvent (2-propanol). The low molecular weight PVAc was then exposed to a range of lipases in different reaction media. When the reaction was carried out in a two-phase organic/aqueous system, lipases from Pseudomonas fluorescens and Rhizopus arrhizus were effective in catalysing partial hydrolysis. On the other hand, these enzymes were not active in THF/butanol medium. In related experiments, e -caprolactone was oligomerized in the presence of pyridine-3-methanol or benzyl alcohol as initiators. In a series of seven lipases, porcine pancreatic lipase and lipase from Candida antarctica gave conversions of monomer that were similar to the traditional metal catalysed polymerizations, when pyridine-3-methanol was used as the initiator. Dibutyl tin oxide gave the highest yields when benzyl alcohol was used as the initiator.

A computer-based system for research in decision making, based on the concept of human problem solvers as builders and users of mental models, is described. This description is presented in three sections: (1) an overview of the behaviors that constitute the cornerstones of human problem solving in realistically complex domains; (2) a brief discussion of the substantive domain selected for studying these behaviors (financial problem solving), detailing the rationale behind its selection; and (3) a comprehensive description of the computerized decision-making system itself. The merits of using HyperCard in such research are discussed in terms of the efficacy and type of data collection engendered.

Cyclic hexapeptides in which the adjacent N e -nitrogens of cyclo -(Lys-Lys-Gly) 2 are cross-linked by p-xylyl or (CH 2 ) 6 units have been prepared. The key steps in the syntheses of these novel types of peptide were the use of tosyl (or, less efficiently, trifluoroacetyl) as N e -protection that allowed intramolecular cross-linking of the tripeptides Boc-Lys(R)-Lys(R)-Gly-OMe (R = Ts or CF 3 CO) using α,ω-dibromo-alkanes/Cs 2 CO 3 , and the efficient cyclo-dimerisation of the pentafluoro-phenyl esters of the resultant cross-linked tripeptides.

Two polycyclic peptides have been prepared in which all four of the e-nitrogens of cyclo -(Lys-Lys-Gly) 2 are interconnected by intra-molecular cross-links. One of these compounds possessed (CH 2 ) 6 units between the adjacent lysyl residues and 4,4′-dimethylenebiphenyl units between the skipped lysyl residues, whilst the other contained p-xylyl units between all four of the lysyl residues.

Analysis of the oligosaccharides released from pig gastric mucus glycopolypeptides by hydrazinolysis showed that degradation had occurred. Nitrosation of the products followed by reduction gave a mixture that had a low content of 2,5-anhydro-D-talitol, which implied destruction of much of the terminal reducing 2-amino-2-deoxy-D-galactose. Under the conditions of hydrazinolysis, cellobiose was largely unchanged but laminaribiose gave a complex mixture that probably contained glucose hydrazone (13C-n.m.r. data). In order to avoid degradation, the hydrazinolysis-nitrosation sequence should be applied to the reduced oligosaccharides released on cleavage with alkali.

Poly(N-isopropylacrylamide)s with imidazole endgroups were used to separate a histidine-tagged protein fragment directly from a crude cell lysate. The polymers display a lower critical solution temperature that can be tuned to occur at a range of subambient temperatures. UV-visible spectra indicated differences in the binding in aqueous media of Cu(II) and Ni(II) to the imidazole endgroups. These changes in the UV-visible spectra were reflected in the solution/aggregation behavior of the polymers as studied by dynamic light scattering. The addition of Cu(II) disaggregated the polymers, and the polymer coil swelled. On the other hand, when Ni(II) was added the polymers remained aggregated in aqueous media. The polymers were used to purify residues 230-534 of the histidine-tagged breast cancer susceptibility protein his6-BRCA1. Cu(II) was found to be better suited to the formation of useful polymer-metal ion-protein complexes that display cloud points, since Ni(II)/polymer mixtures generated very little purified protein. The polymers were synthesized using a previously reported variation of the reversible addition-fragmentation chain termination (RAFT) methodology, using the chain transfer agent 3H-imidazole-4-carbodithioic acid 4-vinyl benzyl ester with N-isopropylacrylamide (NIPAM).

The frictional behaviour of end-grafted poly[2-(dimethyl amino)ethyl methacrylate] films (brushes) has been shown by friction force microscopy to be a strong function of pH in aqueous solution. Data were acquired using bare silicon nitride and gold-coated tips, and gold coated probes that were functionalized by the deposition of self-assembled monolayers. At the extremes of pH (pH = 1, 2, and 12), the friction-load relationship was found to be linear, in agreement with Amontons' law of macroscopic friction. However, at intermediate pH values, the data were fitted by single asperity contact mechanics models; both Johnson-Kendall-Roberts (JKR) and Derjaguin-Muller-Toporov models were observed, with JKR behaviour fitting the data better at relatively neutral pH.

We describe the first example of particulate materials that can detach cultured cells and then release them intact in a temperature controlled manner. Topologically open microgels composed of water swollen highly branched polymers prepared from poly(N-isopropylacrylamide) (PNIPAM) were modified with a cell-adhesive peptide (GRGDS) to produce particles for gently detaching and then transferring cultured cells to new substrates. The particles bind to cell surface integrins on both dermal fibroblasts and endothelial cells and at temperatures above the lower critical solution temperature (34 °C) remove cells from their normal culture substrates. Brief (45 min) cooling of the resultant particle–cell dispersion to beneath 34 °C releases the cells to grow on new substrates. This avoids the need for trypsinisation to detach cells or centrifugation to collect cells post-detachment and offers a flexible approach to cell detachment and transport which is compatible with normal cell culture methodologies.

Decapitation resulted in a time-dependent production of inositol phosphates in rat brain. This production was analyzed by measuring both the radioactivity and the concentrations of inositol phosphates generated from [3H]inositol-labeled phospholipids. Both measurements produced the same time-dependent changes, including a rapid decrease in inositol 1,4,5-trisphosphate within 1.5 min, a 6-fold increase in inositol 1,4-bisphosphate to a maximum at 1.5 min, a 5-fold rise in inositol 4-monophosphate to a maximum at 2.5 min, and little change in inositol 1-monophosphate. The temporal changes in the mass and radioactivity of these compounds, together with the decrease in labeling of phosphatidylinositol 4,5-bisphosphates, support the idea that the inositol phosphates originate from the hydrolysis of phosphatidylinositol 4,5-bisphosphates and not from either the direct hydrolysis of phosphatidylinositol 4-phosphates or phosphatidylinositols.

Highly branched poly(N-isopropyl acrylamide-co-1,2 propandiol-3-methacrylate)s with imidazole end groups and containing anthramethyl methacrylate (AMMA) were prepared. The branch points were produced by incorporating a styryl dithioate ester (a RAFT monomer). The inclusion of AMMA ensures that the polymers fluoresce in the blue region so that they can be visualized in cells in culture. The feed composition was designed to provide lower critical solution temperatures (LCST) between 30 and 37 °C, and therefore the polymers are above the LCST at the usual temperature for culture of human cells. Inclusion of 1,2 propandiol-3-methacrylate (GMA) results in the formation of stable aggregates above the LCST rather than flocculated masses of polymer, and these colloidally stable sub-micron particles can undergo phagocytosis into human dermal fibroblasts. The phagocytosis is temperature dependant and does not occur below the LCST (at 30 °C) when the polymers are in the open-chain fully solvated and non-aggregated state.

The effect of luminal application of arachidonic acid on the alkaline secretion, prostaglandin generation, and mucus glycoprotein output and composition was studied in proximal and distal duodenum of conscious dogs. Surgically prepared duodenal loops were instilled in vivo for up to 2 h with saline (control) followed by various concentrations (12.5-100 micrograms/ml) of arachidonic acid. The experiments were conducted with and without intravenous pretreatment with indomethacin. The recovered instillates were assayed for the content of prostaglandin and HCO3-, and used for the isolation of mucus glycoprotein. Exposure of duodenal mucosa to arachidonic acid led to concentration-dependent increase in the output of HCO3- and prostaglandin generation. In both cases this response was greater in the proximal duodenum. Pretreatment with indomethacin caused reduction in the basal HCO3- and prostaglandin output, and prevented the increments evoked by arachidonic acid. The proximal and distal duodenum displayed similar basal output and composition of mucus glycoprotein. Comparable increases in these glycoproteins were also obtained with arachidonic acid, the effect of which was abolished by indomethacin. Compared to basal conditions, mucus glycoproteins elaborated in response to arachidonic acid exhibited higher contents of associated lipids and covalently bound fatty acids, and contained less protein. The associated lipids of mucus glycoproteins elaborated in the presence of arachidonic acid showed enrichment in phospholipids and decrease in neutral lipids. The carbohydrate components in these glycoproteins also exhibited higher proportions of sialic acid and sulfate. The changes brought about by arachidonic acid were prevented by indomethacin pretreatment, and in both cases the glycoprotein composition returned to that obtained under basal conditions. The enrichment of mucus glycoprotein in lipids, sialic acid and sulfate in response to endogenous prostaglandin may be of significance to the function of this glycoprotein in the hostile environment of the duodenum.

It may seem odd to precede an article with a chronology, but it is odder still that to date no chronology has been published on Lorraine Hansberry. This failure in scholarship is symptomatic of the continuing critical and scholarly neglect of important black artists and especially of Hansberry. During the fifteen years since her death, the only attempt at a formally structured, "lengthy" biography was Catherine Scheader's They Found a Way: Lorraine Hansberry, a recently published seventy-eight page book which (though informative and accurate) was intended for children. Moreover, Robert Nemiroff's informal biography, To Be Young, Gifted and Black (a juxtaposition of Hansberry's autobiographical writings with portions of her essays, speeches, poetry and dramatic scenes), was ignored by critics, receiving no review in the Nezv York Times or any of the major news magazines and scholarly journals. Similarly, few books on American or twentieth-century drama mention Hansberry, and these cite only her pioneering role in black drama with A Raisin in the Sun. The time is long past due to give her the treatment accorded to other major twentiethcentury dramatists. An accurate Hansberry chronology is needed, in part, to correct the enormous amount of misinformation about her. She did not, for example, meet her husband, Robert Nemiroff, while working as a waitress in a restaurant owned by his family, as implied in Current Biography 1959; neither did she own slum property, as Harold Cruse maliciously asserted in The Crisis of the Negro Intellectual. In addition, even a rudimentary chronology should help to clear away the general ignorance of her many radical activities which has permitted critics and students-on too many occasions-to succumb to the myth that Hansberry was an "establishment artist," less interested in changing the system than in getting a home in suburbia, a television, and two cars. An examination of her funeral, by itself, would preclude a facile acceptance of this myth since representatives MELUS, Volume 7, No. 3, Fall 1980

Les Blancs offers Lorraine Hansberry's most detailed and penetrating analysis of colonialism and neo-colonialism in Africa, greatly expanding the commentary begun by Joseph Asagai in A Raisin in the Sun. Both the structure of the play (with its echoes of Hamlet and The Oresteian Trilogy) and direct statements by her major characters link these recent evils committed by whites against blacks to past and present ones committed by whites against whites. This implies that neither the oppression of blacks nor their resistance to it is a unique or an exotic phenomenon. She thus gives the lie to the legion of critics of African and Afro-American literature who have insisted that when blacks write about their oppression they are being provincial and limited. Far from being exotic creatures driven by inner and outer forces unknown to the rest of mankind, blacks have felt the same resentment at exploitation and humiliation as Spartacus, Joan of Arc, Thomas Paine, Garibaldi and Gandhi and the same need to struggle against it. As Hansberry argued in an interview with Eleanor Fisher for CBC on July 6, 1961, there is probably nothing "more universal in the world than man's oppression of man" and "this is what most great dramas have been about, no matter what the device of telling it is." Most critics have noted in passing that there are parallels between Les Blancs and Hamlet. However, these parallels deserve to be explored in some detail, not least because they help to clarify or support Hansberry's view of colonialism. For example, her attack on colonialism is strengthened by her portrayal of the colonial powers who seized control over African lands and peoples as counterparts to the usurper Claudius who seized his brother's throne by murdering him. Moreover, she points up the full viciousness and insidiousness in the cooptation of some Africans, such as Abioseh Matoseh, into the colonial power structure by comparing this to Claudius' manipulation of Laertes into fighting on the side of his true enemy, Claudius himself, against a fellow victim, Hamlet.