Correlating Gene Transfection Efficiency and the Physical Properties of Various Cationic Poly(methacrylate) Systems

Transfection efficiencies of several polymeric gene carriers were compared and correlated quantitatively to the amounts of cellular accumulation of plasmid DNA and to the expression of mRNA by quantitative real time PCR. Three cationic methacrylate polymer systems with similar chemical structure were used in this study, namely: poly(dimethylamino)ethyl methacrylate (PDMA) homopolymer, PEO-b-PDMA copolymer and PEO-b-poly(diethylamino)ethyl methacrylate (PEO-b-PDEA) copolymer. Despite their similar chemical structures, their transfection efficiencies were significantly different. PEO-b-PDEA copolymer was significantly less efficient as gene carrier compared to both PDMA and PEO-b-PDMA systems. Results from quantitative real-time polymerase chain reaction (real-time PCR), cytotoxicity and Zeta potential measurements showed correlations between the physical properties of the polymers and the efficiencies of cellular uptake of the transgene and transfections. In the case of PEO-b-PDEA system, cytotoxicity was due primarily to the excess polymers that did not participate in the DNA binding. In addition, the inability of the polymer/DNA complexes to interact with cell effectively was identified as the main barrier for high efficiency of transfection. This study demonstrated that the use of quantitative real-time PCR in combination with other physical characterization techniques can provide greater insights into the transfection barrier at different cellular levels.Singapore-MIT Alliance (SMA

Association Behavior of Biotinylated and Non-Biotinylated PolyEthylene Oxide-b-Poly(2-(Diethylamino)Ethyl Methacrylate)

Biotinylated and non-biotinylated copolymers of ethylene oxide (EO) and 2-(diethylamino)ethyl methacrylate (DEAEMA) were synthesized by the atom transfer radical polymerization technique (ATRP). The chemical compositions of the copolymers as determined by NMR are represented by PEO₁₁₃PDEAEMA₇₀ and biotin-PEO₁₀₄PDEAEMA₉₃ respectively. The aggregation behavior of these polymers in aqueous solutions at different pHs and ionic strengths was studied using a combination of potentiometric titration, dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM). Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers form micelles at high pH with hydrodynamic radii (Rh) of about 19 and 23 nm, respectively. At low pH, the copolymers are dispersed as unimers in solution with Rh of about 6-7 nm. However, at a physiological salt concentration (cs) of about 0.16M NaCl and a pH of 7-8, the copolymers form large loosely packed Guassian chains, which were not present at the low cs of 0.001M NaCl. The critical micelle concentrations (CMC) and the cytotoxicity of the copolymers were investigated to determine a suitable polymer concentration range for future biological applications. Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers possess identical CMC values of about 0.0023 mg/g, while the cytotoxicity test indicated that the copolymers are not toxic up to 0.05mg/g (> 83% cell survival at this concentration).Singapore-MIT Alliance (SMA

MicroRNA expression in lymphocyte development and malignancy

This article is available open access through the publisher’s website. Copyright @ 2008 Macmillan Publishers Limited.No abstract available.The Leukemia Research Fund, the Julian Starmer-Smith Memorial Fund, and the Medical Research Council

Determinants of intraregional migration in Sub-Saharan Africa 1980-2000

Despite great accomplishments in the migration literature, the determinants of South-South migration remain poorly understood. In an attempt to fill this gap, this paper formulates and tests an empirical model for intraregional migration in sub-Saharan Africa within an extended human capital framework, taking into account spatial interaction. Using bilateral panel data between 1980 and 2000, we find that intraregional migration on the subcontinent is predominantly driven by economic opportunities and sociopolitics in the host country, facilitated by geographical proximity. The role played by network effects and environmental conditions is also apparent. Finally, origin and destination spatial dependence should definitely not be ignored

Hemigrapsus takanoi Asakura and Watanabe, 2005 (Crustacea: Decapoda: Brachyura: Grapsoidea): first records of the brush-clawed shore crab from Great Britain

The brush-clawed shore crab is reported from the River Medway, Kent and the River Colne, Essex, England. These represent the first records of Hemigrapsus takanoi Asakura and Watanabe, 2005 from Great Britain. If H. takanoi becomes established in GB, it may pose a threat to populations of the native shore crab Carcinus maenas

Opening Heaven's Door: Public Opinion and Congressional Votes on the 1965 Immigration Act

The 1965 Immigration Act represented a radical shift in US policy, which has been credited with dramatically expanding the volume and changing the composition of immigration. Its passing has often been described as the result of political machinations negotiated within Congress, without regard to public opinion. We show that congressional voting was consistent with public opinion on abolishing the country-of-origin quotas but not with the desire to limit the volume of immigration. While the former initially reflected attitudes over civil rights, the latter is consistent with contemporary expectations that the expansion in numbers would be modest

Soft and rigid core latex nanoparticles prepared by RAFT-mediated surfactant-free emulsion polymerization for cellulose modification – a comparative study

Latex nanoparticles comprising cationically charged coronas and hydrophobic cores with different glass transition temperatures (Tg) have been prepared by surfactant-free, RAFT-mediated emulsion polymerization, where the particles form through a polymerization-induced self-assembly (PISA) type mechanism. Poly(2-dimethylaminoethyl methacrylate-co-methacrylic acid) (P(DMAEMA-co-MAA)) was utilized as a hydrophilic macroRAFT agent for the polymerization of methyl methacrylate (MMA) or n-butyl methacrylate (nBMA), respectively, resulting in two different latexes, with either a core of high (PMMA) or low (PnBMA) Tg polymer. By varying the molar mass of the hydrophobic block, latexes of different sizes were obtained (DHca. 40–120 nm). The adsorption of the latexes to cellulose model surfaces and cellulose nanofibrils (CNF) was studied using quartz crystal microbalance with dissipation monitoring (QCM-D). The surfaces with adsorbed PnBMA latexes yielded hydrophobic surfaces both before and after annealing, whereas surfaces with adsorbed PMMA latex became hydrophobic only after annealing, clearly showing the influence of the Tg of the core. The latexes were also used to modify macroscopic cellulose in the form of filter papers. Similar to the CNF surfaces, no annealing was required to achieve hydrophobic surfaces with PnBMA latexes. Finally, nanocomposites of CNF and the polymer nanoparticles were prepared through a one-pot mixing procedure. It was found that the largest synthesized PMMA latex (120 nm) facilitated a more strainable CNF network at 50% relative humidity, with a nearly 200% increase in strain at break compared to the neat CNF reference film as well as to the composite films with PnBMA latexes or to the smaller sized PMMA latexes. This difference was attributed to the spherical shape and rigidity of the large PMMA latex nanoparticles during composite formation. This highly interesting result should indeed be considered in the future design of novel biocomposites.</p

Using metacognitive strategies in teaching to facilitate understanding of light concepts among year 9 students

Background: Enhancing students’ metacognitive abilities will help to facilitate their understanding of science concepts. Purpose: The study was designed to conduct and evaluate the effectiveness of a repertoire of interventions aimed at enhancing secondary school students’ metacognitive capabilities and their achievements in science. Sample: A class of 35 Year 9 students participated in the study. Design and methods: The study involved a pre-post design, conducted by the first author as part of the regular designated science programme in a class taught by him. In order to enhance the students’ metacognitive capabilities, the first author employed clearly stated focused outcomes, engaging them in collaborative group work, reading scientific texts and using concept mapping techniques during classroom instruction. The data to evaluate the effectiveness of the metacognitive interventions were obtained from pre- and post-test results of two metacognitive questionnaires, the Metacognitive Support Questionnaire (MSpQ) and the Metacognitive Strategies Questionnaire (MStQ), and data from interviews. In addition, pre-test and post-test scores were used from a two-tier multiple-choice test on Light.Results: The results showed gains in the MSpQ but not in the MStQ. However, the qualitative data from interviews suggested high metacognitive capabilities amongst the high- and average-achieving students at the end of the study. Students’ gains were also evident from the test scores in the Light test. Conclusion: Although the quantitative data obtained from the Metacognitive Strategies Questionnaire did not show significant gains in the students’ metacognitive strategies, the qualitative data from interviews suggested positive perceptions of students’ metacognitive strategies amongst the high- and average-achieving students. Data from the Metacognitive Support Questionnaire showed that there were significant gains in the students’ perceptions of their metacognitive support implying that the majority of the students perceived that their learning environment was oriented towards the development of their metacognitive capabilities. The effect of the metacognitive interventions on students’ achievement in the Light test resulted in students displaying the correct declarative knowledge, but quite often they lacked the procedural knowledge by failing to explain their answers correctly

Analytic and numerical realisations of a disk galaxy

Recent focus on the importance of cold, unshocked gas accretion in galaxy formation -- not explicitly included in semi-analytic studies -- motivates the following detailed comparison between two inherently different modelling techniques: direct hydrodynamical simulation and semi-analytic modelling. By analysing the physical assumptions built into the Gasoline simulation, formulae for the emergent behaviour are derived which allow immediate and accurate translation of these assumptions to the Galform semi-analytic model. The simulated halo merger history is then extracted and evolved using these equivalent equations, predicting a strikingly similar galactic system. This exercise demonstrates that it is the initial conditions and physical assumptions which are responsible for the predicted evolution, not the choice of modelling technique. On this level playing field, a previously published Galform model is applied (including additional physics such as chemical enrichment and feedback from active galactic nuclei) which leads to starkly different predictions.Comment: 15 pages, 15 figure

Commercials, careers and culture: travelling salesmen in Britain 1890s-1930s

Within the lower middle-class, British commercial travellers established a strong fraternal culture before 1914. This article examines their interwar experiences in terms of income, careers, and associational culture. It demonstrates how internal labour markets operated, identifies the ways in which commercial travellers interpreted their role, and explores their social and political attitudes