Molecular weight effects on the phase morphology of PS/P4VP blend films on homogeneous SAM and heterogeneous SAM/Au substrates

The effects of the molecular weight of polystyrene (PS) component on the phase separation of PS/poly(4-vinylpyridine) (PS/P4VP) blend films on homogeneous alkanethiol self-assembled monolayer (SAM) and heterogeneous SAM/Au substrates have been investigated by means of atomic force microscopy (AFM). For the PS (22.4k)/P4VP (60k) system, owing to the molecular weight of PS component is relatively small, the well-aligned PS and P4VP stripes with good thermal stability are directed by the patterned SAM/Au surfaces. With the increase of the molecular weight of PS component (for the PS (582k)/P4VP (60k) system), the diffusion of P4VP is hindered by the high viscosity of PS during the fast spin-coating process. The phase separation behavior of PS/P4VP on the SAM/Au patterned substrates is similar to that on the homoueneous SAM and cannot be easily directed by the patterned SAM surfaces even though the characteristic length of the lateral domain morphology is commensurate with the stripe width.

Statistical thermodynamics of polydisperse polymer systems in the framework of lattice fluid model: Effect of molecular weight and its distribution on the spinodal in polymer solution

With the aid of thermodynamics of Gibbs, the expression of the spinodal was derived for the polydisperse polymer-solvent system in the framework of Sanchez-Lacombe Lattice Fluid Theory (SLLFT). For convenience, we considered that a model polydisperse polymer contains three sub-components. According to our calculation, the spinodal depends on both weight-average ((M) over bar (w)) and number-average ((M) over bar (n)) molecular weights of the polydisperse polymer, but the z-average molecular weight ((M) over bar (z)) dependence on the spinodal is invisible. The dependence of free volume on composition, temperature, molecular weight, and its distribution results in the effect of (M) over bar (n) on the spinodal. Moreover, it has been found that the effect of changing (M) over bar (w) on the spinodal is much bigger than that of changing (M) over bar (n) and the extrema of the spinodal increases with the rise of the weight-average molecular weight of the polymer in the solutions with upper critical solution temperature (UCST). However, the effect of polydispersity on the spinodal can be neglected for the polymer with a considerably high weight-average molecular weight. A more simple expression of the spinodal for the polydisperse polymer solution in the framework of SLLFT was also derived under the assumption of upsilon(*)=upsilon(1)(*)=upsilon(2)(*) and (1/r(1)(0))-(1/r(2i)(0))-->(1/r(1)(0)).

Determination of purity and molecular weight of calmodulin by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

The purity and molecular weight of calmodulin have been determined by means of matrix-assisted laser desorption/ionization time of flight mass spectrometry, and the results have been discussed. The experimental results demonstrate that this method is high sensitive and rapid as compared with other traditional methods.

Impact behavior of phenolphthalein poly(ether sulfone) ultrahigh molecular weight polyethylene blends

This work presents the structure and impact properties of phenolphthalein poly(ether sulfone) blended with ultrahigh molecular weight polyethylene (PES-C/UHMWPE) at different compositions. The addition of UHMWPE can considerably improve the Charpy and Izod impact strength of the blends. The fracture surface is examined to demonstrate the toughening mechanics related to the modified PES-C resin. (C) 1998 John Wiley & Sons, Inc.

MOLECULAR-WEIGHT DEPENDENCE OF THE GLASS-TRANSITION OF CYCLIC POLYSTYRENE

The glass transition temperature (T(g)) of cyclic polystyrene was measured by differential scanning calorimetry. There was a marked difference in the glass transition behaviour between cyclic and linear polystyrene. In the low molecular weight region (M(n) < 5 x 10(3)), the T(g) of the cyclic polystyrene increased with decreasing M(n), contrary to that of linear polystyrene. With M(n) higher than 5 x 10(3), the T(g) of cyclic polystyrene increased with increasing M(n). The T(g) of cyclic and linear polystyrene approached the same constant value when the M(n) was high enough (M(n) > 10(5)). Combining the results of specific volume, it is believed that the variation of T(g) with molecular weight does not depend only on free volume effects but that configurational entropy is also an important factor.

Antioxidant activity of different molecular weight sulfated polysaccharides from Ulva pertusa Kjellm (Chlorophyta)

Polysaccharides extracted from Ulva pertusa Kjellm ( Chlorophyta) are a group of sulfated heteropolysaccharides, the ulvans. In this study, different molecular weight ulvans were prepared by H2O2 degradation and their antioxidant activities investigated including superoxide and hydroxyl radical scavenging activity, reducing power and metal chelating ability. The molecular weights of natural and degraded ulvans were 151.7, 64.5, 58.0, and 28.2 kDa, respectively, as determined by high performance gel permeation chromatography. Among the four samples, U-3 ( the lowest molecular weight sample) showed significant inhibitory effects on superoxide and hydroxyl radicals with IC50 values of 22.1 mu g mL(-1) and 2.8 mg mL(-1); its reducing power and metal chelating ability were also the strongest among the four samples. All the other samples also demonstrated strong activity against superoxide radicals. The results indicated that molecular weight had a significant effect on the antioxidant activity of ulvan with low molecular weight ulvan having stronger antioxidant activity.

Rapid separation of biologically important low molecular weight compounds by microchip electrophoresis and ultra-fast performance liquid chromatography

The research work in this thesis reports rapid separation of biologically important low molecular weight compounds by microchip electrophoresis and ultrahigh liquid chromatography. Chapter 1 introduces the theory and principles behind capillary electrophoresis separation. An overview of the history, different modes and detection techniques coupled to CE is provided. The advantages of microchip electrophoresis are highlighted. Some aspects of metal complex analysis by capillary electrophoresis are described. Finally, the theory and different modes of the liquid chromatography technology are presented. Chapter 2 outlines the development of a method for the capillary electrophoresis of (R, S) Naproxen. Variable parameters of the separation were optimized (i.e. buffer concentration and pH, concentration of chiral selector additives, applied voltage and injection condition).The method was validated in terms of linearity, precision, and LOD. The optimized method was then transferred to a microchip electrophoresis system. Two different types of injection i.e. gated and pinched, were investigated. This microchip method represents the fastest reported chiral separation of Naproxen to date. Chapter 3 reports ultra-fast separation of aromatic amino acid by capillary electrophoresis using the short-end technique. Variable parameters of the separation were optimized and validated. The optimized method was then transferred to a microchip electrophoresis system where the separation time was further reduced. Chapter 4 outlines the use of microchip electrophoresis as an efficient tool for analysis of aluminium complexes. A 2.5 cm channel with linear imaging UV detection was used to separate and detect aluminium-dopamine complex and free dopamine. For the first time, a baseline, separation of aluminium dopamine was achieved on a 15 seconds timescale. Chapter 5 investigates a rapid, ultra-sensitive and highly efficient method for quantification of histamine in human psoriatic plaques using microdialysis and ultrahigh performance liquid chromatography with fluorescence detection. The method utilized a sub-two-micron packed C18 stationary phase. A fluorescent reagent, 4-(1-pyrene) butyric acid N-hydroxysuccinimide ester was conjugated to the primary and secondary amino moieties of histamine. The dipyrene-labeled histamine in human urine was also investigated by ultrahigh pressure liquid chromatography using a C18 column with 1.8 μm particle diameter. These methods represent one of the fastest reported separations to date of histamine using fluorescence detection.

Low molecular weight halocarbons in the Humber and Rhine estuaries determined using a new purge-and-trap gas chromatographic method

A number of chlorinated and brominated low molecular weight hydrocarbons (halocarbons) have been measured in and adjacent to the North Sea estuaries of the Humber and the Rhine. The measurements have been carried out using a newly constructed purge-and-trap sample work-up system coupled to megabore gas chromatography with electron capture detection. The results show that whereas the Humber is a pronounced source of the anthropogenic halocarbons carbon tetrachloride and perchloroethylene, the input from the Rhine into the North Sea of these compounds is more modest. Some halocarbons normally considered as mainly or even exclusively of natural origin are released from the two investigated estuaries into the North Sea. A distinct patch of high concentrations of the naturally produced compound bromoform was observed in the southwestern North Sea. The results have also been used to examine some of the halocarbons for common sources.

Use of a novel micro-fluidic device to create arrays for multiplex analysis of large and small molecular weight compounds by surface plasmon resonance

There is an increasing demand to develop biosensor monitoring devices capable of biomarker profiling for predicting animal adulteration and detecting multiple chemical contaminants or toxins in food produce. Surface plasmon resonance (SPR) biosensors are label free detection systems that monitor the binding of specific biomolecular recognition elements with binding partners. Essential to this technology are the production of biochips where a selected binding partner, antibody, biomarker protein or low molecular weight contaminant, is immobilised. A micro-fluidic immobilisation device allowing the covalent attachment of up to 16 binding partners in a linear array on a single surface has been developed for compatibility with a prototype multiplex SPR analyser.

The immobilisation unit and multiplex SPR analyser were respectively evaluated in their ability to be fit-for-purpose for binding partner attachment and detection of high and low molecular weight molecules. The multiplexing capability of the dual technology was assessed using phycotoxin concentration analysis as a model system. The parent compounds of four toxin groups were immobilised within a single chip format and calibration curves were achieved. The chip design and SPR technology allowed the compartmentalisation of the binding interactions for each toxin group offering the added benefit of being able to distinguish between toxin families and perform concentration analysis. This model is particularly contemporary with the current drive to replace biological methods for phycotoxin screening.

Adiponectin multimers, body weight and markers of cardiovascular risk in adolescence: Northern Ireland Young Hearts Project:Northern Ireland Young Hearts Project

Background:Research examining the relationship between adiponectin (AN) isoforms, body weight and cardiovascular (CV) risk factors is limited, particularly in younger populations. Objectives:To investigate the inter-relationships between AN isoforms and CV risk factors, and their dependence on body weight status, in adolescents. Design:Blood samples from 92 obese, 92 overweight and 92 normal weight age- and sex-matched adolescents were analysed for traditional cardiovascular disease (CVD) risk biomarkers and also total, high molecular weight (HMW), medium and low molecular weight (LMW) AN. Results:A significant inverse association was observed between total and HMW AN and waist-hip ratio (P=0.015, P=0.006, respectively), triglycerides (P=0.003, P=0.003, respectively) and systolic blood pressure (P=0.012, P=0.024, respectively) and a significant positive association with high-density lipoprotein (P<0.001, P<0.001, respectively) in multi-adjusted analyses. There was no evidence of a relationship between multimeric AN and high-sensitivity C-reactive protein. There was also little evidence of a relationship between LMW AN and CVD risk factors. There was a strong, body mass index (BMI)-independent, association between AN, CVD biomarkers and the hypertriglyceridemic waist phenotype. Conclusion:Prominent, BMI-independent associations between total and HMW AN, but not LMW AN, and CVD risk factors were already evident in this young population. This research in adolescents supports the contention that AN subfractions may have different biological actions. These associations in apparently healthy adolescents suggest an important role for AN and its subfractions in the pathogenesis of metabolic syndrome traits and indicate that the potential for total or HMW AN to act as early universal biomarkers of CV risk warrants further study.

Progress in the development of immunoanalytical methods incorporating recombinant antibodies to small molecular weight biotoxins

Rapid immunoanalytical screening of food and environmental samples for small molecular weight (hapten) biotoxin contaminations requires the production of antibody reagents that possess the requisite sensitivity and specificity. To date animal-derived polyclonal (pAb) and monoclonal (mAb) antibodies have provided the binding element of the majority of these assays but recombinant antibodies (rAb) isolated from in vitro combinatorial phage display libraries are an exciting alternative due to (1) circumventing the need for experimental animals, (2) speed of production in commonly used in vitro expression systems and (3) subsequent molecular enhancement of binder performance. Short chain variable fragments (scFv) have been the most commonly employed rAb reagents for hapten biotoxin detection over the last two decades but antibody binding fragments (Fab) and single domain antibodies (sdAb) are increasing in popularity due to increased expression efficiency of functional binders and superior resistance to solvents. rAb-based immunochromatographic assays and surface plasmon resonance (SPR) biosensors have been reported to detect sub-regulatory levels of fungal (mycotoxins), marine (phycotoxins) and aquatic biotoxins in a wide range of food and environmental matrices, however this technology has yet to surpass the performances of the equivalent mAb- and pAb-based formats. As such the full potential of rAb technology in hapten biotoxin detection has yet to be achieved, but in time the inherent advantages of engineered rAb are set to provide the next generation of ultra-high performing binder reagents for the rapid and specific detection of hapten biotoxins.

Relação do aroma e da espuma dos vinhos espumantes com o potencial enológico das uvas e dos vinhos

Os espumantes produzidos segundo o método Champanhês são obtidos após uma segunda fermentação em garrafa. Quando o vinho é vertido no copo, o CO2 produzido é libertado, sendo a espuma formada o resultado da sua interacção com os constituintes do vinho. A quantidade e a estabilidade da espuma do vinho espumante estão relacionadas com a sua composição química. Para além da espuma, o aroma é também um parâmetro importante de qualidade na apreciação geral de um vinho espumante. O aroma de um vinho espumante provém do contributo das uvas assim como do processo fermentativo. Dependendo do estado de maturação da uva, o contributo dos compostos voláteis para o aroma é diferente. Em virtude da vindima para os vinhos espumantes ser realizada antes da vindima para os vinhos maduros, dependendo da variedade, as uvas poderão não ser colhidas na expressão máxima do seu aroma, podendo verificar-se uma perda significativa do seu potencial varietal volátil. O objectivo desta dissertação é relacionar o aroma e a espuma dos vinhos espumantes com o potencial enológico das uvas e dos vinhos. Para isso, foi estudada a composição volátil das duas castas principais da Bairrada, a casta branca Fernão-Pires (FP) e a casta tinta Baga (BG), sendo estas duas das castas usadas para a produção de espumante. Para estudar a composição volátil das uvas durante a maturação, com vista a avaliar este efeito na expressão máxima de compostos voláteis, foi optimizada para este propósito a metodologia de microextracção em fase sólida em espaço de cabeça (HS-SPME). As uvas foram colhidas semanalmente, em duas vinhas, do pintor à pós-maturidade sendo posteriormente analisadas pela metodologia de HS-SPME seguida de cromatografia de gás acoplada à espectrometria de massa com quadrupolo (GC–qMS). No caso das uvas BG, observou-se um aumento acentuado na expressão máxima de compostos voláteis próximo da maturidade da uva determinada pelo teor em açúcar e acidez titulável, mantendo-se constante durante a pós-maturidade. Na determinação do perfil volátil das uvas ao longo da maturação foram identificados 66 compostos varietais nas uvas provenientes de uma vinha (Pedralvites) e 45 da outra vinha (Colégio). Em ambas as vinhas foram identificados 23 sesquiterpenóides, 13 monoterpenóides, 6 norisoprenóides, 2 álcoois aromáticos e 1 diterpenóide. Os sesquiterpenóides, devido à sua abundância em número e em área cromatográfica, podem ser considerados marcadores da casta BG. As uvas FP apresentaram um comportamento diferente do das uvas BG, sendo a expressão máxima de compostos voláteis expressa durante um curto período de tempo (1 semana), que coincide com a maturidade da uva. Depois de atingido este pico, observa-se uma diminuição drástica logo na semana seguinte. Este comportamento foi observado em ambas as vinhas, onde foram identificados 20 compostos voláteis varietais e 5 pré-fermentativos (álcoois e aldeídos em C6). Estes resultados mostram que quando estas castas são colhidas precocemente (1 semana antes da maturidade) para a produção de espumante, é observada uma redução significativa do potencial volátil que é expresso na maturidade. Para a análise da composição volátil dos vinhos espumantes foi optimizada uma metodologia de microextracção que permite usar uma maior quantidade de fase estacionária, a extracção sorptiva em barra de agitação (SBSE). O método foi optimizado usando 10 padrões de compostos voláteis representativos das principais famílias químicas presentes no vinho, nomeadamente, ésteres, monoterpenóides, sesquiterpenóides, norisoprenóides em C13 e álcoois. O método proposto apresenta uma boa linearidade (r2 > 0,982) e a reprodutibilidade varia entre 8,9 e 17,8%. Os limites de detecção para a maioria dos compostos é bastante baixo, entre 0,05 e 9,09 μg L-1. O método foi aplicado para a análise da composição volátil dos vinhos espumantes. Dentro dos vinhos espumantes analisados, foi estudada a influência da casta, do tipo de solo e do estado de maturação das uvas na sua composição volátil. A casta FP pode dar origem a vinhos com maior potencial de aroma do que a casta BG. Relativamente à avaliação dos diferentes estados de maturação, verificou-se que as uvas da maturidade e as da colheita tardia (uma semana depois da maturidade) deram origem aos vinhos com maior quantidade de compostos voláteis. Para os três tipos de solo estudados (arenoso, argiloso e argilo-calcário), o vinho obtido a partir de uvas colhidas no solo argilo-calcário foi o que mostrou a maior concentração de compostos voláteis varietais. A espuma destes vinhos espumantes foi também avaliada quanto à sua quantidade máxima (HM) e tempo de estabilidade (TS). O vinho espumante que apresentou um maior TS foi o vinho produzido a partir da casta FP proveniente de uma colheita tardia e solo argiloso. Os vinhos provenientes dos solos arenosos e argilo-calcários são os que apresentaram valores mais baixos de TS. Com vista a avaliar quais os conjuntos de moléculas do vinho que estão relacionados com as propriedades da espuma e possíveis sinergismos entre eles, para cada vinho espumante foi separada a fracção hidrofóbica de baixo peso molecular (MeLMW), a fracção de elevado peso molecular (HMW) e duas fracções de peso molecular intermédio (AqIMW e MeIMW). As propriedades da espuma dos vinhos modelo, reconstituídos com estas fracções e suas misturas, foram avaliadas. A combinação da fracção HMW com a MeLMW aumentou o TS 2,7 vezes quando comparado com o observado para a fracção HMW isoladamente, produzindo um efeito sinergético. Este aumento do TS ainda foi maior quando se combinou a fracção HMW com as subfracções obtidas a partir da fracção MeLMW, principalmente para as fracções menos apolares. A subfracção hidrofóbica menos apolar foi caracterizada por espectrometria de massa de ionização por electrospray (ESI-MS/MS) tendo sido identificada uma série de oligómeros de polietileno glicol e um potencial composto tensioactivo, o 8-hidroxi-tridecanoato de dietilenoglicolglicerilacetato. A fracção MeLMW foi também isolada da espuma do vinho espumante e caracterizada por ESI-MS/MS, permitindo identificar vários compostos potenciais tensioactivos, nomeadamente, dois monoacilgliceróis e quatro derivados de ácidos gordos com gliceriletilenoglicol. Estes resultados confirmam que estes compostos relacionados com a estabilidade da espuma existem em maior número na espuma do que no vinho. O vinho foi ainda fraccionado em 12 grupos de moléculas: 3 fracções de manoproteínas, 3 de arabinogalactanas, 3 de misturas de polissacarídeos, proteínas e compostos fenólicos e 3 fracções de peso molecular intermédio e baixo, compostas por uma mistura de hidratos de carbono, peptídeos e compostos fenólicos. Foram usados vinhos modelo reconstituídos com cada uma das fracções isoladas na concentração em que estas se encontraram no vinho. Foram também efectuados ensaios com soluções modelo dez vezes mais concentradas e com misturas de algumas das fracções. Todas as soluções formadas foram avaliadas quanto às propriedades da espuma. O aumento da concentração para dez vezes faz com que a solução contendo a fracção rica em manoproteínas (MP1) aumente para mais do dobro a HM e 7,4 vezes mais o TS. A combinação entre a fracção MP1 e a MeLMW produziu um aumento significativo nos parâmetros de HM e TS. A combinação da fracção HMW (manoproteínas com baixo teor em proteína) com a MeLMW (tensioactivos derivados de ácidos gordos com gliceriletilenoglicol) contém os compostos chave de um vinho espumante para se obter uma maior quantidade e estabilidade da espuma.

Effect of heat on rheology, surface hydrophobicity and molecular weight distribution of glutens extracted from flours with different bread-making quality

Gluten was extracted from flours of several different wheat varieties of varying baking quality. Creep compliance was measured at room temperature and tan 6 was measured over a range of temperatures from 25 to 95 degrees C. The extracted glutens were heat-treated for 20 min at 25, 40, 50, 60, 70 and 90 degrees C in a water bath, freeze-dried and ground to a fine powder. Tests were carried out for extractability in sodium dodecyl sulphate, free sulphydryl (SH) groups using Ellman's method, surface hydrophobicity and molecular weight (MW) distribution (MWD) using field-flow fractionation and multi-angle laser light scattering. With increasing temperature, the glutens showed a decrease in extractability, with the most rapid decreases occurring between 70 and 90 degrees C, a major transition in tan 6 at around 60 degrees C and a minor transition at 40 degrees C for most varieties, a decrease in free SH groups and surface hydrophobicity and a shift in the MWD towards higher MW. The poor bread-making variety Riband showed the highest values of tan delta and Newtonian compliance, the lowest content of free SH groups and the largest increase of HMW/LMW with increasing temperature. No significant correlations with baking volume were found between any of the measured parameters. (c) 2007 Elsevier Ltd. All rights reserved.

Wheat glutenin proteins assemble into a nanostructure with unusual structural features

The proteins of wheat have a known propensity to aggregate into a variety of forms. We report here a novel nanostructure from wheat proteins, derived from a crude extract of high molecular weight glutenins. The structure was characterised by a significant thioflavin T (ThT) fluorescence and a fibrillar morphology by transmission electron microscopy (TEM). The ThT fluorescence and TEM data are suggestive of an amyloid structure, but the X-ray fibre diffraction data show a reflection pattern (4.02, 4.2-4.3, 4.6, 12.9,19.3 and 38.7 angstrom) inconsistent with both the classic amyloid form and the previously described beta-helix structure. The 4.6 angstrom reflection is consistent with that predicted for the amyloid inter-beta-strand, and the absence of the inter-beta-sheet distance at approximate to 10-11 angstrom is not unprecedented in amyloid-like structures. However, our observed X-ray reflection pattern has not been previously reported and suggests a novel wheat glutenin nanostructure. (C) 2008 Elsevier Ltd. All rights reserved.