Why is the condensed phase of DNA preferred at higher temperature? DNA compaction in the presence of a multivalent cation

Upon the addition of multivalent cations, a giant DNA chain exhibits a large discrete transition from an elongated coil into a folded compact state. We performed single-chain observation of long DNAs in the presence of a tetravalent cation (spermine), at various temperatures and monovalent salt concentrations. We confirmed that the compact state is preferred at higher temperatures and at lower monovalent salt concentrations. This result is interpreted in terms of an increase in the net translational entropy of small ions due to ionic exchange between higher and lower valence ions.Comment: 4pages,3figure

Fast responsive and morphologically robust thermo-responsive hydrogel nanofibres from poly(N-isopropylacrylamide) and POSS crosslinker

Stable thermo-responsive hydrogel nanofibres have been prepared by electrospinning of commercial poly(N-isopropylacrylamide) (PNIPAM) in the presence of a polyhedral oligomeric silsesquioxane (POSS) possessing eight epoxide groups and of an organic-base catalyst, followed by a heat curing treatment. The nanofibres showed excellent hydrogel characteristics with fast swelling and de-swelling responses triggered by temperature changes. They were also morphologically robust as their physical integrity was preserved upon repeated hydration/dehydration cycles and exposure to solvents.<br /

Multi-stimuli-responsive Self-immolative Polymer Assemblies

Self-immolative polymers (SIPs) undergo depolymerization in response to the cleavage of stimuli-responsive end-caps from their termini. Some classes of SIPs, including polycarbamates, have depolymerization rates that depend on environmental factors such as solvent and pH. In previous work, hydrophobic SIPs have been incorporated into amphiphilic block copolymers and used to prepare nanoassemblies. However, stimuli-responsive hydrophilic blocks have not previously been incorporated. In the current work, we synthesized amphiphilic copolymers composed of a hydrophobic polycarbamate SIP block and a hydrophilic poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) block connected by a UV light-responsive linker end-cap. It was hypothesized that after assembly of the block copolymers into nanoparticles, chain collapse of the PDMAEMA above its lower critical solution temperature (LCST) might change the environment of the SIP block, thereby altering its depolymerization rate. Self-assembly of the block copolymers was performed, and the depolymerization of the resulting assemblies was studied by fluorescence spectroscopy, dynamic light scattering, and NMR spectroscopy. At 20 °C, the system exhibited a selective response to the UV light. At 65 °C, above the LCST of PDMAEMA, the systems underwent more rapid depolymerization, suggesting that the increase in rate arising from the higher temperature dominated over environmental effects arising from chain collapse

Thermally Responsive Amphiphilic Conetworks and Gels Based on Poly(N‑isopropylacrylamide) and Polyisobutylene

Novel amphiphilic conetworks (APCN) consisting of thermoresponsive poly(N-isoproplyacrylamide) (PNiPAAm) cross-linked by hydrophobic methacrylate-telechelic polyisobutylene (MA-PIB-MA) were successfully synthesized in a broad composition range. The resulting PNiPAAm-l-PIB conetworks (“l” stands for “linked by”) were obtained by radical copolymerization of NiPAAm with MA-PIB-MA in tetrahydrofuran, a cosolvent for all the components. Low amounts of extractables substantiated efficient network formation. The composition dependent two glass transition temperatures (Tg) by DSC analysis indicate microphase separation of the cross-linked components without mixed phases. It was found that the PNiPAAm-l-PIB conetworks are uniformly swellable in both water and n-hexane; i.e., these new materials behave either as hydrogels or as hydrophobic gels in aqueous or nonpolar media, respectively. The uniform swelling in both polar and nonpolar solutes indicates cocontinuous (bicontinuous) phase morphology. The equilibrium swelling degrees (R) depend on composition, that is, the higher the PIB content, the lower the R in water and the higher in n-hexane. The PNiPAAm phase keeps its thermoresponsive behavior in the conetworks as shown by significant decrease of the swelling degree in water between 20 and 35 °C. The lower critical solubility temperature (LCST) values determined by DSC are found to decrease from 34.1 °C (for the pure PNiPAAm homopolymer) to the range of 25–28 °C in the conetworks, and the extent of the LCST decrease is proportional with the PIB content. Deswelling-swelling, i.e., heating–cooling, cycle indicates insignificant hysteresis in these new thermoresponsive materials. This indicates that PNiPAAm-l-PIB conetworks with predetermined and thermoresponsive swelling behavior can be designed and utilized in several advanced applications on the basis of results obtained in the course of this study

Photonic hydrogel sensors

Analyte-sensitive hydrogels that incorporate optical structures have emerged as sensing platforms for point-of-care diagnostics. The optical properties of the hydrogel sensors can be rationally designed and fabricated through self-assembly, microfabrication or laser writing. The advantages of photonic hydrogel sensors over conventional assay formats include label-free, quantitative, reusable, and continuous measurement capability that can be integrated with equipment-free text or image display. This Review explains the operation principles of photonic hydrogel sensors, presents syntheses of stimuli-responsive polymers, and provides an overview of qualitative and quantitative readout technologies. Applications in clinical samples are discussed, and potential future directions are identified

Promoting reuse behaviour: Challenges and strategies for repeat purchase, low-involvement products

Reusable products offer reduced environmental impact compared to recycling, but producers mostly focus on strategies such as light-weighting, recyclability and eco-labelling. A reasonable number of innovative reusable products and business models exist for repeat purchase, low-involvement products, but they are largely restricted to niche health-food stores. Therefore, this research primarily attempts to understand consumer attitudes and behaviour towards reuse of household care products (e.g. air fresheners, domestic cleaning products). Focus groups with UK consumers are utilised to examine reusable/refillable spray products and the data are triangulated with global archival data on various refill business models, reusable products and recycling initiatives. The study offers useful guidelines for both producers and policy makers to encourage reusable products. First, we recommend that eco-innovations have a familiar design congruent with well-known brands, to reduce uncertainties for consumers. Second, if the innovation has an unfamiliar design, to mitigate, producers should offer new functional benefits. Third, and most important, producers must place greater emphasis on aesthetic aspects that could evoke product attachment, thus encouraging reuse. Fourth, if reusable products are to become mainstream, ‘well-known brands’ have to promote the transition from one-off sales to a service model built on durable products. Finally, a successful outcome is dependent on government interventions in designing new life cycle policy instruments, in particular de-marketing the current recycling norm and emphasising reusing over recycling