Synthesis of strained macrocyclic biaryls for enthalpy-driven ring-opening polymerization

Polymerizable macrocyclic biarylene-ether-ketones and biarylene-ether-sulfones are accessible from linear, bis(chloro)-terminated oligomers via nickel-catalyzed, intramolecular coupling under pseudo-high-dilution conditions. Single-crystal X-ray analyses of the resulting cyclo-oligomers reveal extremely distorted and highly strained geometries, with 4,4 '-biphenylene units showing deviations of up to 70 degrees from linearity.

Spontaneous ring-opening polymerization of macrocyclic aromatic thioether ketones under transient high-temperature conditions

Spontaneous ring-opening polymerization of macrocyclic aromatic thioether ketones [-1,4-SC6H4CO-C6H4-](n) (n = 3 and 4), in which the thioether linkages are para to the ketone, occurs during rapid, transient heating to 480degreesC, to afford a soluble, semi-crystalline poly(thioether ketone) of high molar mass (eta(inh) > 1.0 dL . g(-1)). Corresponding macrocyclic ether ketone, and a macrocyclic thioether ether ketone in which the thioether linkage is para to the ether rather than to the ketone, show no evidence of polymerization under analogous conditions.

Intermediate ion stability and regio selectivity polymerization using neutral salicyladiminato in propene nickel(II) and palladium(II) complexes as catalysts

The mechanism of the Heck reaction has been studied with regard to transition metal catalysis of the addition of propene and the formation of unsaturated polymers. The reactivity of nickel and palladium complexes with five different bidentate ligands with O,N donor atoms has been investigated by computational methods involving density functional theory. Hence, it is possible to understand the electronic and steric factors affecting the reaction and their relative importance in determining the products formed in regard of their control of the regiochemistry of the products. Our results show that whether the initial addition of propene is trans to O or to N of the bidentate ligand is of crucial importance to the subsequent reactions. Thus when the propene is trans to 0, 1,2-insertion is favoured, but when the propene is trans to N, then 2,1-insertion is favoured. This difference in the preferred insertion pathway can be related to the charge distribution engendered in the propene moiety when the complex is formed. Indeed charge effects are important for catalytic activity but also for regioselectivity. Steric effects are shown to be of lesser importance even when t-butyl is introduced into the bidentate ligand as a substituent. (C) 2007 Elsevier B.V. All rights reserved.

The crucial importance of agostic interactions in intermediates formed in propylene polymerization using neutral salicyladiminato palladium(II) and nickel complexes as catalysts

The structures of intermediates formed in propylene polymerisation using neutral salicyladiminato palladium(II) and nickel(II) complexes as catalysts have been investigated using density functional theory. Calculations show that all low energy intermediates contain agostic interactions either between the metal and a hydrogen from the added propylene forming four- or five-membered chelate rings, or, when a phenyl ring is present, between the metal and an aromatic C-C bond. The agostic interactions with the metal are concomitant with changes in ligand dimensions and electronic properties. In particular when a metal to hydrogen bond is formed, there is a lengthening of the C-H bond. Significant differences are found for the agostic interactions with palladium and nickel in that for Pd there is a clear preference for specific intermediates but for Ni there are several different structures with similar energies which are likely to lead to a greater variety of products on further polymerisation. (c) 2007 Elsevier B.V. All rights reserved.

A DFT study of propylene polymerization using neutral salicyladiminato nickel(II) and palladium(II) as catalysts

Propylene polymerization using salicyladiminato metal catalalysts has been studied using density functional theory at the B3LYP/LANL2DZ level. In particular, the effects on the reaction mechanisms of changing the metal from Pd(II) to Ni(II) have been investigated. While the reaction mechanisms involving the salicyladiminato Ni(II) catalyst have been found to be similar to those established previously for the salicyladiminato Pd(II) catalyst, the nickel catalyst was found to differentiate the trans-O intermediate from the trans-.N intermediate with an energy difference of 46.63 U mol(-1) significantly more than the palladium catalyst for which the energy difference was calculated as 35.82 kJ mol(-1). The energy difference between the trans-O configuration and the trans-N configuration is decreased significantly when combining a molecule of propylene with the catalyst. For the Ni catalyst, the trans-O isomer is more stable than the trans-N isomer to a greater extent than for Pd, so that the insertion of propylene from 20 is relatively less favoured for Ni than for Pd. It is predicted that the mechanism of isomerization from 20 to 2N through a rotational transition state TS2O2N is more appropriate for the Ni catalyst system. The palladium system shows a larger preference for pi-coordination than its nickel counterpart, although the latter possesses a lower reaction barrier. It was found that the occupation of the trans-O position in the asymmetric salicyladiminato catalyst is also more favored by the alkene as it is by the alkyl so that insertion of the alkene may always start from a particular configuration so that specific products are obtained. (c) 2005 Elsevier B.V. All rights reserved.

Thermo-responsive poly(methyl methacrylate)-block-poly(N-isopropylacrylamide) block copolymers synthesized by RAFT polymerization: micellization and gelation

RAFT polymerization was used to prepare PMMA-b-PNIPAM copolymers. Two different chain transfer agents, tBDB and MCPDB, were used to mediate the sequential polymerizations. Micellar solutions and gels were prepared from the resulting copolymers in aqueous solution. When heated above T-c of PNIPAM (about 31 degrees C), DLS revealed that PNIPAM coronas collapsed, resulting in aggregation of the original micelles. The micellar gels underwent syneresis above T-c as water was expelled from the ordered gel structure, the lattice periodicity of which was determined by SANS. A large decrease in lattice spacing was observed above T-c. The gel became more viscoelastic at high temperature, as revealed by shear rheometry which showed a large increase in G".

Thermal Fractionation and isothermal crystallization of polyethylene nanocomposites prepared by in situ polymerization

Nanocomposites of high-density polyethylene (HDPE) and carbon nanotubes (CNT) of different geometries (single wall, double wall, and multiwall; SWNT, DWNT, and MWNT) were prepared by in situ polymerization of ethylene on CNT whose surface had been previously treated with a metallocene catalytic system. In this work, we have studied the effects of applying the successive self-nucleation and annealing thermal fractionation technique (SSA) to the nanocomposites and have also determined the influence of composition and type of CNT on the isothermal crystallization behavior of the HDPE. SSA results indicate that all types of CNT induce the formation of a population of thicker lamellar crystals that melt at higher temperatures as compared to the crystals formed in neat HDPE prepared under the same catalytic and polymerization conditions and subjected to the same SSA treatment. Furthermore, the peculiar morphology induced by the CNT on the HDPE matrix allows the resolution of thermal fractionation to be much better. The isothermal crystallization results indicated that the strong nucleation effect caused by CNT reduced the supercooling needed for crystallization. The interaction between the HDPE chains and the surface of the CNT is probably very strong as judged by the results obtained, even though it is only physical in nature. When the total crystallinity achieved during isothermal crystallization is considered as a function of CNT content, it was found that a competition between nucleation and topological confinement could account for the results. At low CNT content the crystallinity increases (because of the nucleating effect of CNT on HDPE), however, at higher CNT content there is a dramatic reduction in crystallinity reflecting the increased confinement experienced by the HDPE chains at the interfaces which are extremely large in these nanocomposites. Another consequence of these strong interactions is the remarkable decrease in Avrami index as CNT content increases. When the Avrami index reduces to I or lower, nucleation dominates the overall kinetics as a consequence of confinement effects. Wide-angle X-ray experiments were performed at a high-energy synchrotron source and demonstrated that no change in the orthorhombic unit cell of HDPE occurred during crystallization with or without CNT.

Rapid, uncatalyzed ring-opening polymerization of individual macrocyclic poly(arylene thioether ketone)s under dynamic heating conditions

Uncatalyzed, ring-opening polymerization of individual macrocyclic poly(arylene thioether ketone)s (1-4) and mixtures (5) under dynamic heating conditions has been demonstrated for the first time. High-molecular-weight, film-forming products were obtained after heating of the macrocycles up to 480 degreesC, with a heating rate of 10-20 degreesC /min. Depending on the macrocyclic structure and heat treatment conditions, the polymers obtained were amorphous or semicrystalline, soluble or slightly crosslinked. NMR analyses of the soluble polymers revealed their linear, highly regular structure. According to NMR, DSC, and TGA studies, the polymers obtained do not contain any residual macrocycles. The polymers with thio-p-arylene moieties in the main chain were thermally stabile. The catalyzed ring opening polymerization of 5 carried out in diphenyl sulfone solution is also reported for comparison. Using quantum mechanical calculations of the ring opening of macrocycles, a reaction mechanism is suggested. Preparation of nanosized poly(thioether ketone) fibrils by a replication method is described.

LIPGENE food-exchange model for alteration of dietary fat quantity and quality in free-living participants from eight European countries

Controlled human intervention trials are required to confirm the hypothesis that dietary fat quality may influence insulin action. The aim was to develop a food-exchange model, suitable for use in free-living volunteers, to investigate the effects of four experimental diets distinct in fat quantity and quality: high SFA (HSFA); high MUFA (HMUFA) and two low-fat (LF) diets, one supplemented with 1.24g EPA and DHA/d (LFn-3). A theoretical food-exchange model was developed. The average quantity of exchangeable fat was calculated as the sum of fat provided by added fats (spreads and oils), milk, cheese, biscuits, cakes, buns and pastries using data from the National Diet and Nutrition Survey of UK adults. Most of the exchangeable fat was replaced by specifically designed study foods. Also critical to the model was the use of carbohydrate exchanges to ensure the diets were isoenergetic. Volunteers from eight centres across Europe completed the dietary intervention. Results indicated that compositional targets were largely achieved with significant differences in fat quantity between the high-fat diets (39.9 (SEM 0.6) and 38.9 (SEM 0.51) percentage energy (%E) from fat for the HSFA and HMUFA diets respectively) and the low-fat diets (29.6 (SEM 0.6) and 29.1 (SEM 0.5) %E from fat for the LF and LFn-3 diets respectively) and fat quality (17.5 (SEM 0.3) and 10.4 (SEM 0.2) %E front SFA and 12.7 (SEM 0.3) and 18.7 (SEM 0.4) %E MUFA for the HSFA and HMUFA diets respectively). In conclusion, a robust, flexible food-exchange model was developed and implemented successfully in the LIPGENE dietary intervention trial.

Successful manipulation of the quality and quantity of fat and carbohydrate consumed by free-living individuals using a food exchange model

Our objective in this study was to develop and implement an effective intervention strategy to manipulate the amount and composition of dietary fat and carbohydrate (CHO) in free-living individuals in the RISCK study. The study was a randomized, controlled dietary intervention study that was conducted in 720 participants identified as higher risk for or with metabolic syndrome. All followed a 4-wk run-in reference diet [high saturated fatty acids (SF)/high glycemic index (GI)]. Volunteers were randomized to continue this diet for a further 24 wk or to I of 4 isoenergetic prescriptions [high monounsaturated fatty acids (MUFA)/high GI; high MUFA/low GI; low fat (LF)/high GI; and LF/low GI]. We developed a food exchange model to implement each diet. Dietary records and plasma phospholipid fatty acids were used to assess the effectiveness of the intervention strategy. Reported fat intake from the LF diets was significantly reduced to 28% of energy (%E) compared with 38% E from the HM and LF diets. SF intake was successfully decreased in the HM and LF diets was similar to 10% E compared with 17% E in the reference diet (P = 0.001). Dietary MUFA in the HIM diets was similar to 17% E, significantly higher than in the reference (12% E) and LF diets (10% E) (P = 0.001). Changes in plasma phospholipid fatty acids provided further evidence for the successful manipulation of fat intake. The GI of the HGI and LGI arms differed by similar to 9 points (P = 0.001). The food exchange model provided an effective dietary strategy for the design and implementation across multiple sites of 5 experimental diets with specific targets for the proportion of fat and CHO. J. Nutr. 139: 1534-1540, 2009.

Lack of effect of dietary n-6 : n-3 PUFA ratio on plasma lipids and markers of insulin responses in Indian Asians living in the UK

Background: Indian Asians living in Western Countries have an over 50% increased risk of coronary heart disease (CHD) relative to their Caucasians counterparts. The atherogenic lipoprotein phenotype (ALP), which is more prevalent in this ethnic group, may in part explain the increased risk. A low dietary long chain n-3 fatty acid (LC n-3 PUFA) intake and a high dietary n-6 PUFA intake and n-6:n-3 PUFA ratio in Indian Asians have been proposed as contributors to the increased ALP incidence and CHD risk in this subgroup. Aim: To examine the impact of dietary n-6:n-3 PUFA ratio on membrane fatty acid composition, blood lipid levels and markers of insulin sensitivity in Indian Asians living in the UK. Methods: Twenty-nine males were assigned to either a moderate or high n-6:n-3 PUFA (9 or 16) diet for 6 weeks. Fasting blood samples were collected at baseline and 6 weeks for analysis of triglycerides, total-, LDL- and HDL- cholesterol, non-esterified fatty acids, glucose, insulin, markers of insulin sensitivity and C-reactive protein. Results: Group mean saturated fatty acid, MUFA, n-6 PUFA and n-3 PUFA on the moderate and high n-6:n-3 PUFA diets were 26 g/d, 43 g/d, 15 g/d, 2 g/d and 25 g/d, 25 g/d, 28 g/d, 2 g/d respectively. A significantly lower total membrane n-3 PUFA and a trend towards lower EPA and DHA levels were observed following the high n-6:n-3 PUFA diet. However no significant effect of treatment on plasma lipids was evident. There was a trend towards a loss of insulin sensitivity on the high n-6:n-3 PUFA diet, with the increase in fasting insulin (P = 0.04) and HOMA IR [(insulin x glucose)/22.5] (P = 0.02) reaching significance. Conclusion: The results of the current study suggest that, within the context of a western diet, it is unlikely that dietary n-6:n-3 PUFA ratio has any major impact on the levels of LC n-3 PUFA in membrane phospholipids or have any major clinically relevant impact on insulin sensitivity and its associated dyslipidaemia.

Relation between the fatty acid composition of peripheral blood mononuclear cells and measures of immune cell function in health free-living subjects aged 25-72 y

Background: There is little information about the relation between the fatty acid composition of human immune cells and the function of those cells over the habitual range of fatty acid intakes. Objective: The objective of the study was to determine the relation between the fatty acid composition of human peripheral blood mononuclear cell (PBMC) phospholipids and the functions of human immune cells. Design: One hundred fifty healthy adult subjects provided a fasting blood sample. The phagocytic and oxidative burst activities of monocytes and neutrophils were measured in whole blood. PBMCs were isolated and used to measure lymphocyte proliferation in response to the T cell mitogen concanavalin A and the production of cytokines in response to concanavalin A or bacterial lipopolysaccharide. The fatty acid composition of plasma and PBMC phospholipids was determined. Results: Wide variations in fatty acid composition of PBMC phospholipids and immune cell functions were identified among the subjects. The proportions of total Polyunsaturated fatty acids (PUFAs), of total n-6 and n-3 PUFAs, and of several individual PUFAs in PBMC phospholipids were positively correlated with phagocytosis by neutrophils and monocytes, neutrophil oxidative burst, lymphocyte proliferation, and interferon gamma production. The ratios of saturated fatty acids to PUFAs and of n-6 to n-3 PUFAs were negatively correlated with these same immune functions. The relation of PBMC fatty acid composition to monocyte oxidative burst was the reverse of its relation to monocyte phagocytosis and neutrophil oxidative burst. Conclusion: Variations in the fatty acid composition of PBMC phospholipids account for some of the variability in immune cell functions among healthy adults.

Dietary PUFA and the metabolic syndrome in Indian Asians living in the UK

Indian Asians living in the UK have a 50% higher CHD mortality rate compared with the indigenous Caucasian population, which cannot be attributed to traditional risk factors. Instead, features of the metabolic syndrome, including raised plasma triacylglycerol, reduced HDL-cholesterol (HDL-C) and an increased proportion of small dense LDL particles, together with insulin resistance and central obesity, are prevalent among this population. The present review examines evidence to support the hypothesis that an imbalance in dietary PUFA intake, specifically a higher intake of n-6 PUFA in combination with a lower intake of the long-chain (LC) n-3 PUFA, plays an important role in the prevalence of the metabolic syndrome observed in Indian Asians. Data are presented to illustrate the impact of manipulation of the background n-6 PUFA intake (moderate or high n-6 PUFA) and the subsequent response to supplementation with LC n-3 PUFA on blood lipids and insulin action in a group of Indian Asian volunteers. The results demonstrate that supplementation with LC n-3 PUFA had no impact on insulin action in those subjects consuming either the moderate-or high-n-6 PUFA diet. In the postprandial phase reductions in plasma triacylglycerol concentrations were greater in those consuming the high-n-6 PUFA background diet subsequent to fish oil supplementation. The present study concludes that, contrary to the central hypothesis, the prevalence of metabolic abnormalities in Indian Asians compared with Caucasians may not be attributable to differences in intakes of n-6 and n-3 PUFA.

Living with ASD: how do children and their parents assess their difficulties with social interaction and understanding?

Social interaction and understanding in autistic spectrum disorder (ASD) are key areas of concern to practitioners and researchers alike. However, there is a relative lack of information about the skills and competencies of children and young people with ASD who access ordinary community facilities including mainstream education. In particular, contributions by parents and their children have been under-utilized. Using two structured questionnaires, 19 children with ASD reported difficulties with social skills including social engagement and temper management and also reported difficulties with social competence, affecting both friendships and peer relationships. Parents rated the children's social skill and competence as significantly worse than did the children themselves, but there was considerable agreement about the areas that were problematic. Using an informal measure to highlight their children's difficulties, parents raised issues relating to conversation skills, social emotional reciprocity and peer relationships. The implications for assessment and intervention are discussed.