Universality of the collapse transition of sticky polymers

The universality of the swelling of the radius of gyration of a homopolymer relative to its value in the $\theta$ state, independent of polymer-solvent chemistry, in the crossover regime between $\theta$ and athermal solvent conditions, is well known. Here we study, by Brownian dynamics, a polymer model where a subset of monomers is labelled as "stickers". The mutual interaction of the stickers is more attractive than those of the other ("backbone") monomers, and has the additional important characteristic of "functionality" $\varphi$, i.e., the maximum number of stickers that can locally bind to a given sticker. A saturated bond formed in this manner remains bound until it breaks due to thermal fluctuations, a requirement which can be viewed as an additional Boolean degree of freedom that describes the bonding. This, in turn, makes the question of the order of the collapse transition a non-trivial one. Nevertheless, for the parameters that we have studied (in particular, $\varphi=1$), we find a standard second-order $\theta$ collapse, using a renormalised solvent quality parameter that takes into account the increased average attraction due to the presence of stickers. We examine the swelling of the radius of gyration of such a sticky polymer relative to its value in the altered $\theta$ state, using a novel potential to model the various excluded volume interactions that occur between the monomers on the chain. We find that the swelling of such sticky polymers is identical to the universal swelling of homopolymers in the thermal crossover regime. Additionally, for our model, the Kuhn segment length under $\theta$ conditions is found to be the same for chains with and without stickers.Comment: 13 pages, 10 figures, supplementary material (see ancillary directory), to appear in Soft Matte

Kinetic and sequence-structure-function analysis of known LinA variants with different hexachlorocyclohexane isomers

BACKGROUND Here we report specific activities of all seven naturally occurring LinA variants towards three different isomers, α, γ and δ, of a priority persistent pollutant, hexachlorocyclohexane (HCH). Sequence-structure-function differences contributing to the differences in their stereospecificity for α-, γ-, and δ-HCH and enantiospecificity for (+)- and (-)-α -HCH are also discussed. METHODOLOGY/PRINCIPAL FINDINGS Enzyme kinetic studies were performed with purified LinA variants. Models of LinA2(B90A) A110T, A111C, A110T/A111C and LinA1(B90A) were constructed using the FoldX computer algorithm. Turnover rates (min(-1)) showed that the LinAs exhibited differential substrate affinity amongst the four HCH isomers tested. α-HCH was found to be the most preferred substrate by all LinA's, followed by the γ and then δ isomer. CONCLUSIONS/SIGNIFICANCE The kinetic observations suggest that LinA-γ1-7 is the best variant for developing an enzyme-based bioremediation technology for HCH. The majority of the sequence variation in the various linA genes that have been isolated is not neutral, but alters the enantio- and stereoselectivity of the encoded proteins.This work was supported by the Indo-Australian Biotechnology Fund from the Department of Education Science and Technology (DEST), Australia and the Department of Biotechnology (DBT), India

Sterols and oxysterols

The ingredients of animal feed formulation, especially the fatty sources, play a significant role in the production of high-quality food of animal origin. Industrial fat by-products are a major source of feeding fats in Europe. The main objectives of the project were firstly to assess feed fats and oils for their composition and content of sterols (cholesterol and phytosterols) and oxysterols, and secondly to assess the levels of cholesterol and oxycholesterols of chicken and rabbit tissues after feeding with especially formulated feeds containing trans fatty acids and oxidized lipids. The lack of standardized analytical procedure prompted the evaluation of an in-house purification method by comparing it with a number of commonly used methods for the analysis of oxysterols. The saponification and transesterification steps showed rather comparable results. A two-dimensional capillary GC column with different stationary phases (a 35% phenyl column coupled to an apolar 5% phenyl column) was used for better resolution of a large number of oxysterols. This new system improved the separation efficiency and reduced the analytical time for a wide range of oxysterols. The satisfactory purification method and the reliable separation of oxysterols facilitated the qualitative and quantitative assessment of sterols and oxysterols in samples of by-products from chemical and physical refining. A large variation in the levels of sterols and oxysterols was observed in the fat by-products from chemical and physical refining processes for edible fats and oils. The observed variations in the contents and composition of sterols and oxysterols were mainly due to the origins, production facility and different processing conditions of the by-product samples. The highly oxidized lipid and trans fatty acid feeds significantly increased the contents of cholesterol and oxycholesterols in edible parts, e.g. the muscles and livers of chickens and rabbits (0.01< p ≤0.05). Hence, the consumption of products from animals fed with higher levels of trans fatty acids and oxidized lipid feeds may contribute to higher ingestion of cholesterol and oxycholesterols by humans

PROMOTING GLOBAL CITIZENSHIP EDUCATION WITH SCIENCE TEACHING AND ANALYSING THE WAY IT IS PERCEIVED BY STUDENTS AT SECONDARY LEVEL

This case study in Dhanbad, India explores 25 grade 9 students’ learning outcomes on the basis of gender and background in Global Citizenship Education related topics of science and also their perceptions about the Global Citizenship Education. It is time that we should realize that education itself has little value if it is merely meant for entrance straightaway into a profession instead we have to value the fact that Education needs to be open to the process of interpretation and complex engagements that is brought by teachers and the pupil within learning relationships. To create opportunity for Global Citizenship Education schools should adopt analytical approaches in knowledge acquisition and incorporate ways of teaching which supports the development of global citizens in educational programs. The study also examines the discourse of international organisations in order to promote better understanding of Global Citizenship Education and the study indicates that international organisations have developed a powerful GCE discourse. We are living in highly interconnected and interdependent world where to determine our collective future, we need to acquire profound understanding of global developments and expand our global consciousness. Findings revealed the existence of difference in knowledge based, value based and citizenship based outcomes of rural and urban background students as well as gender based differences were also found

Is There an Association between Work Stress and Diurnal Cortisol Patterns? Findings from the Whitehall II Study.

The evidence on whether there is work stress related dysregulation of the hypothalamic-pituitary-adrenal axis is equivocal. This study assessed the relation between work stress and diurnal cortisol rhythm in a large-scale occupational cohort, the Whitehall II study