Reversible addition fragmentation chain transfer (RAFT) polymerization : mechanism, process and applications

The present article gives an overview of the reversible addition fragmentation chain transfer (RAFT) process. RAFT is one of the most versatile living radical polymerization systems and yields polymers of predictable chain length and narrow molecular weight distribution. RAFT relies on the rapid exchange of thiocarbonyl thio groups between growing polymeric chains. The key strengths of the RAFT process for polymer design are its high tolerance of monomer functionality and reaction conditions, the wide range of well-controlled polymeric architectures achievable, and its (in-principle) non-rate-retarding nature. This article introduces the mechanism of polymerization, the range of polymer molecular weights achievable, the range of monomers in which polymerization is controlled by RAFT, the various polymeric architectures that can be obtained, the type of end-group functionalities available to RAFT-made polymers, and the process of RAFT polymerization.

Polymer nanocarrier system for endosome escape and timed release of siRNA with complete gene silencing and cell death in cancer cells

An influenza virus-inspired polymer mimic nanocarrier was used to deliver siRNA for specific and near complete gene knockdown of an osteoscarcom cell line (U-2SO). The polymer was synthesized by single-electron transfer living radical polymerization (SET-LRP) at room temperature to avoid complexities of transfer to monomer or polymer. It was the only LRP method that allowed good block copolymer formation with a narrow molecular weight distribution. At nitrogen to phosphorus (N/P) ratios of equal to or greater than 20 (greater than a polymer concentration of 13.8 μg/mL) with polo-like kinase 1 (PLK1) siRNA gave specific and near complete (>98%) cell death. The polymer further degrades to a benign polymer that showed no toxicity even at polymer concentrations of 200 μg/mL (or N/P ratio of 300), suggesting that our polymer nanocarrier can be used as a very effective siRNA delivery system and in a multiple dose administration. This work demonstrates that with a well-designed delivery device, siRNA can specifically kill cells without the inclusion of an additional clinically used highly toxic cochemotherapeutic agent. Our work also showed that this excellent delivery is sensitive for the study of off-target knockdown of siRNA.

Kinetic analysis of nitroxide radical coupling reactions mediated by CuBr

In a previous paper, we described the room temperature rapid, selective, reversible, and near quantitative Cu-activated nitroxide radical coupling (NRC) technique to prepare 3-arm polystyrene stars. In this work, we evaluated the Cu-activation mechanism, either conventional atom transfer or single electron transfer (SET), through kinetic simulations. Simulation data showed that one can describe the system by either activation mechanism. We also found through simulations that bimolecular radical termination, regardless of activation mechanism, was extremely low and could be considered negligible in an NRC reaction. Experiments were carried out to form 2- and 3-arm PSTY stars using two ligands, PMDETA and Me6TREN, in a range of solvent conditions by varying the ratio of DMSO to toluene, and over a wide temperature range. The rate of 2- or 3-arm star formation was governed by the choice of solvent and ligand. The combination of Me6TREN and toluene/DMSO showed a relatively temperature independent rate, and remarkably reached near quantitative yields for 2-arm star formation after only 1 min at 25 °C.

Living characteristics of the free-radical ring-closing polymerization of diallyldimethylammonium chloride

In this communication we provide the most recent results on RAFT-mediated ring-closing polymerization of diallyldimethylammonium chloride (DADMAC). The polymerization was carried out in aqueous solution employing 2,2′-azobis(2-methylpropionamidine)-dihydrochloride as the free radical initiator and trithiocarbonate RAFT agent (2-{[(dodecylsulfanyl)carbonothioyl sulfanyl]}propanoic acid, DoPAT) as the controlling RAFT agent. The results show that – while the system is not as completely controlled as previously described – it is nevertheless possible to mediate the polymerization of DADMAC and impart some living characteristics onto the system. The initial study on the RAFT-mediated polymerization of DADMAC may have overestimated the degree of livingness within this reaction. However, it is possible – at low conversions – for some living characteristics to be observed, as the evolution of molecular weight with conversion is linear. In addition, polymers with a reasonably narrow polydispersity can be isolated.

Abatement of aqueous anionic contaminants by thermo-responsive nanocomposites: (Poly(N-isopropylacrylamide))-co-silylanized Magnesium/Aluminun layered double hydroxides

A series of novel thermo-responsive composite sorbents, were prepared by free-radical co-polymerization of N-isopropylacrylamide (NIPAm) and the silylanized Mg/Al layered double hydroxides (SiLDHs), named as PNIPAm-co-SiLDHs. For keeping the high affinity of Mg/Al layered double hydroxides towards anions, the layered structure of LDHs was assumed to be reserved in PNIPAm-co-SiLDHs by the silanization of the wet LDH plates as evidenced by the X-ray powder diffraction. The sorption capacity of PNIPAm-co-SiLDH (13.5 mg/g) for Orange-II from water was found to be seven times higher than that of PNIPAm (2.0 mg/g), and the sorption capacities of arsenate onto PNIPAm-co-SiLDH are also greater than that onto PNIPAm, for both As(III) and As(V). These sorption results suggest that reserved LDH structure played a significant role in enhancing the sorption capacities. NO3− intercalated LDHs composite showed the stronger sorption capacity for Orange-II than that of CO32−. After sorption, the PNIPAm-co-SiLDH may be removed from water because of its gel-like nature, and may be easily regenerated contributing to the accelerated desorption of anionic contaminants from PNIPAm-co-SiLDHs by the unique phase-transfer feature through slightly heating (to 40 °C). These recyclable and regeneratable properties of thermo-responsive nanocomposites facilitate its potential application in the in-situ remediation of organic and inorganic anions from contaminated water.

Brucite Microbialites in Living Coral Skeletons: Indicators of Extreme Microenvironments in Shallow-Marine Settings

Brucite [Mg(OH)2] microbialites occur in vacated interseptal spaces of living scleractinian coral colonies (Acropora, Pocillopora, Porites) from subtidal and intertidal settings in the Great Barrier Reef, Australia, and subtidal Montastraea from the Florida Keys, United States. Brucite encrusts microbial filaments of endobionts (i.e., fungi, green algae, cyanobacteria) growing under organic biofilms; the brucite distribution is patchy both within interseptal spaces and within coralla. Although brucite is undersaturated in seawater, its precipitation was apparently induced in the corals by lowered pCO2 and increased pH within microenvironments protected by microbial biofilms. The occurrence of brucite in shallow-marine settings highlights the importance of microenvironments in the formation and early diagenesis of marine carbonates. Significantly, the brucite precipitates discovered in microenvironments in these corals show that early diagenetic products do not necessarily reflect ambient seawater chemistry. Errors in environmental interpretation may arise where unidentified precipitates occur in microenvironments in skeletal carbonates that are subsequently utilized as geochemical seawater proxies.

Being and Living in an Australian Urban Community

There is a limited evidence base which highlights the plight of Australian Aboriginal and Torres Strait Islander populations living in urban areas and the issues that impact on Indigenous achievements in education, health status, housing needs, rates of incarceration and the struggle for cultural recognition. This is despite over 70 % of all Aboriginal and Torres Strait Islander people in Australia now living in urban or regional urban areas (ABS 2008). The statistics demonstrate that living in urban centres is as much part of reality for Australian Aboriginal and Torres Strait Islander people as living in a remote discrete community. Using the capital city of Brisbane, Queensland as a case study, this paper will explore some of the issues that Aboriginal and Torres Strait Islander peoples face against a backdrop of the statistics and some of the current literature. It will additionally explore why there has been limited research with Aboriginal and Torres Strait Islander populations in urban areas and highlight some of the innovative research taking place which will begin to redress this gap. The research issues presented within this paper will resonate with some of the Native American and Indigenous movement patterns and associated issues additionally occurring in the United States of America, Canada and New Zealand.

My place through my eyes : a social constructionist approach to researching the relationships between socioeconomic living contexts and physical activity

There is a growing evidence-base in the epidemiological literature that demonstrates significant associations between people’s living circumstances – including their place of residence – and their health-related practices and outcomes (Leslie, 2005; Karpati, Bassett, & McCord, 2006; Monden, Van Lenthe, & Mackenbach, 2006; Parkes & Kearns, 2006; Cummins, Curtis, Diez-Roux, & Macintyre, 2007; Turrell, Kavanagh, Draper, & Subramanian, 2007). However, these findings raise questions about the ways in which living places, such as households and neighbourhoods, figure in the pathways connecting people and health (Frolich, Potvin, Chabot, & Corin, 2002; Giles-Corti, 2006; Brown et al, 2006; Diez Roux, 2007). This thesis addressed these questions via a mixed methods investigation of the patterns and processes connecting people, place, and their propensity to be physically active. Specifically, the research in this thesis examines a group of lower-socioeconomic residents who had recently relocated from poorer suburbs to a new urban village with a range of health-related resources. Importantly, the study contrasts their historical relationship with physical activity with their reactions to, and everyday practices in, a new urban setting designed to encourage pedestrian mobility and autonomy. The study applies a phenomenological approach to understanding living contexts based on Berger and Luckman’s (1966) conceptual framework in The Social Construction of Reality. This framework enables a questioning of the concept of context itself, and a treatment of it beyond environmental factors to the processes via which experiences and interactions are made meaningful. This approach makes reference to people’s histories, habituations, and dispositions in an exploration between social contexts and human behaviour. This framework for thinking about context is used to generate an empirical focus on the ways in which this residential group interacts with various living contexts over time to create a particular construction of physical activity in their lives. A methodological approach suited to this thinking was found in Charmaz’s (1996; 2001; 2006) adoption of a social constructionist approach to grounded theory. This approach enabled a focus on people’s own constructions and versions of their experiences through a rigorous inductive method, which provided a systematic strategy for identifying patterns in the data. The findings of the study point to factors such as ‘childhood abuse and neglect’, ‘early homelessness’, ‘fear and mistrust’, ‘staying indoors and keeping to yourself’, ‘conflict and violence’, and ‘feeling fat and ugly’ as contributors to an ongoing core category of ‘identity management’, which mediates the relationship between participants’ living contexts and their physical activity levels. It identifies barriers at the individual, neighbourhood, and broader ecological levels that prevent this residential group from being more physically active, and which contribute to the ways in which they think about, or conceptualise, this health-related behaviour in relationship to their identity and sense of place – both geographic and societal. The challenges of living well and staying active in poorer neighbourhoods and in places where poverty is concentrated were highlighted in detail by participants. Participants’ reactions to the new urban neighbourhood, and the depth of their engagement with the resources present, are revealed in the context of their previous life-experiences with both living places and physical activity. Moreover, an understanding of context as participants’ psychological constructions of various social and living situations based on prior experience, attitudes, and beliefs was formulated with implications for how the relationship between socioeconomic contextual effects on health are studied in the future. More detailed findings are presented in three published papers with implications for health promotion, urban design, and health inequalities research. This thesis makes a substantive, conceptual, and methodological contribution to future research efforts interested in how physical activity is conceptualised and constructed within lower socioeconomic living contexts, and why this is. The data that was collected and analysed for this PhD generates knowledge about the psychosocial processes and mechanisms behind the patterns observed in epidemiological research regarding socioeconomic health inequalities. Further, it highlights the ways in which lower socioeconomic living contexts tend to shape dispositions, attitudes, and lifestyles, ultimately resulting in worse health and life chances for those who occupy them.

Similarity not favourability : the role of donor prototypes in predicting willingness to donate organs while living

Using an extended Prototype/Willingness Model, we examined the predictors of willingness to donate an organ to a partner/family member and a stranger while living. A questionnaire assessed university students’ (N = 284) attitudes, subjective norm, prototype favourability, prototype similarity, moral norm, and willingness to donate organs in each recipient scenario. All variables, except prototype favourability, predicted willingness to donate organs in both situations. Future strategies should emphasise perceived approval from important others for living donation, the consistency of living donation with one’s own morals, and encourage perceptions of similarity between oneself and living donors to increase acceptance of living donation.

Knowing a donor and identifying as one : determinants of people's willingness for related and anonymous living donation in Australia

While LRD (living donation to a genetically/emotionally related recipient) is well established in Australia, LAD (living anonymous donation to a stranger) is rare. Given the increasing use of LAD overseas, Australia may likely follow suit. Understanding the determinants of people’s willingness for LAD is essential but infrequently studied in Australia. Consequently, we compared the determinants of people’s LRD and LAD willingness, and assessed whether these determinants differed according to type of living donation. We surveyed 487 health students about their LRD and LAD willingness, attitudes, identity, prior experience with blood and organ donation, deceased donation preference, and demographics. We used Structural Equation Modelling (SEM) to identify the determinants of willingness for LRD and LAD and paired sample t-tests to examine differences in LRD and LAD attitudes, identity, and willingness. Mean differences in willingness (LRD 5.93, LAD 3.92), attitudes (LRD 6.43, LAD 5.53), and identity (LRD 5.69, LAD 3.58) were statistically significant. Revised SEM models provided a good fit to the data (LRD: x2 (41) = 67.67, p = 0.005, CFI = 0.96, RMSEA = 0.04; LAD: x2 (40) = 79.64, p < 0.001, CFI = 0.95, RMSEA = 0.05) and explained 45% and 54% of the variation in LRD and LAD willingness, respectively. Four common determinants of LRD and LAD willingness emerged: identity, attitude, past blood donation, and knowing a deceased donor. Religious affiliation and deceased donation preference predicted LAD willingness also. Identifying similarities and differences in these determinants can inform future efforts aimed at understanding people’s LRD and LAD willingness and the evaluation of potential living donor motives. Notably, this study highlights the importance of people’s identification as a living donor as a motive underlying their willingness to donate their organs while living.