Bacteriorhodopsin (bR) is a light-driven proton pump and a model membrane transport protein. We used time-resolved serial femtosecond crystallography at an x-ray free electron laser to visualize conformational changes in bR from nanoseconds to milliseconds following photoactivation. An initially twisted retinal chromophore displaces a conserved tryptophan residue of transmembrane helix F on the cytoplasmic side of the protein while dislodging a key water molecule on the extracellular side. The resulting cascade of structural changes throughout the protein shows how motions are choreographed as bR transports protons uphill against a transmembrane concentration gradient.
Temperature-responsive intelligent surfaces, prepared by the modification of an interface with poly(N-isopropylacrylamide) and its derivatives, have been used for biomedical applications. Such surfaces exhibit temperature-responsive hydrophilic/hydrophobic alterations with external temperature changes, which, in turn, result in thermally modulated interactions with biomolecules and cells. In this review, we focus on the application of these intelligent surfaces to chromatographic separation and cell cultures. Chromatographic separations using several types of intelligent surfaces are mentioned briefly, and various effects related to the separation of bioactive compounds are discussed, including wettability, copolymer composition and graft polymer architecture. Similarly, we also summarize temperature-responsive cell culture substrates that allow the recovery of confluent cell monolayers as contiguous living cell sheets for tissue-engineering applications. The key factors in temperature-dependent cell adhesion/detachment control are discussed from the viewpoint of grafting temperature-responsive polymers, and new methodologies for effective cell sheet culturing and the construction of thick tissues are summarized.
Dense poly(N-isopropylacrylamide) (PIPAAm) brushes were created on silica bead surfaces by surface-initiated atom transfer radical polymerization (ATRP). Interfacial properties of PIPAAm brushes were characterized by thermoresponisve interaction with biomolecules. The grafted amounts of PIPAAm on silica bead surfaces exceeded that from previously reported polymer-hydrogel-modified silica beads prepared by conventional radical polymerization by nearly 1 order of magnitude. Temperature-dependent chromatographic interactions with soluble analytes were modulated by changing the grafted PIPAAm chain lengths. Short PIPAAm-grafted silica beads produce insufficient dehydration and chain aggregation to separate steroids using weak hydrophobic interactions. In contrast, broad unresolved peaks were observed on silica beads column grafted with long PIPAAm chains due to steroid partitioning into thick, densely grafted PIPAAm brush layers. Thus, silica beads column grafted with PIPAAm chains of proper length can demonstrate baseline separation of steroids with relatively high resolution among the tested columns. Relatively longer retention times for steroid analytes were observed on all columns compared to those previously reported for other PIPAAm-grafted silica beads. This indicates that densely PIPAAm-grafted chains enable control of strong hydrophobic interactions with steroids by changing the column temperature. Densely grafted PIPAAm columns were also successful in separating two peptides into two peaks as the column temperature was increased to 40 degrees C. This provides an effective separation alternative for peptides using substantial hydrophobicity without modification of hydrophobic surfaces and/or low mobile phase pH. In conclusion, densely PIPAAm-grafted surfaces exhibit strong, reversible temperature-modulated hydrophobic interactions, facilitating baseline separations of steroids and peptides in aqueous milieu without changes in the mobile phase pH and high ionic strength.
We have prepared various poly(N-isopropylacrylamide) (PIPAAm)-grafted silica bead surfaces through surface-initiated atom transfer radical polymerization (ATRP) by changing graft densities and brush chain lengths. The prepared surfaces were characterized by chromatographic analysis using the modified silica beads as chromatographic stationary phases. ATRP initiator (2-(m,p-chloromethylphenyl)ethyltrichlorosilane) density on silica bead surfaces was modulated by changing the feed composition of the self-assembled monolayers (SAMs) of mixed silane coupling agents consisting of ATRP initiator and phenethyltrichlorosilane on the surfaces. IPAAm was then polymerized on SAM-modified silica bead surfaces by ATRP in 2-propanol at 25 degrees C. The chain length of the grafted PIPAAm was controlled by simply changing the ATRP reaction time at constant catalyst concentration. The thermoresponsive surface properties of the PIPAAm-grafted silica beads were investigated by temperature-dependent elution behavior of hydrophobic steroids from the surfaces using Milli-Q water as a mobile phase. On the surfaces grafted with shorter PIPAAm chains, longer retention times for steroids were observed on sparsely grafted PIPAAm surfaces compared to dense PIPAAm brushes at low temperature, because of hydrophobic interactions between the exposed phenethyl groups of SAMs on silica surfaces and steroid molecules. Retention times for steroids on dilute PIPAAm chain columns decreased with temperature similarly to conventional reverse-phase chromatographic modes on octadecyl columns. This effect was due to limited interaction of solutes with the PIPAAm-grafted surfaces. Retention times for steroids on dilute PIPAAm brush surfaces with longer PIPAAm chains became greater above the PIPAAm transition temperature. At low-temperature regions, hydrated and expanded PIPAAm at low temperatures prevented hydrophobic interactions between the phenethyl group of SAMs on the silica bead surfaces and steroid molecules. Retention times for steroids on a dense PIPAAm brush column increased with temperature since solvated polymer segments within the dense brush layer undergo dehydration over a broad range of temperatures. In conclusion, PIPAAm graft density has a crucial influence on the elution behavior of steroids because of the interaction of analytes with silica bead interfaces, and because of the characteristic dehydration of PIPAAm in dense-pack brush surfaces.
BackgroundSchool children have been increasingly recognized as health messengers for malaria control. However, little evidence is available. The objective of this study was to determine the impact of school-based malaria education intervention on school children and community adults.MethodsThis study was conducted in the Dangme-East district of the Greater Accra Region, Ghana, between 2007 and 2008. Trained schoolteachers designed participatory health education activities and led school children to disseminate messages related to malaria control to their communities. Three schools and their respective communities were chosen for the study and assigned to an intervention group (one school) and a control group (two schools). Questionnaire-based interviews and parasitological surveys were conducted before and after the intervention, with the intervention group (105 children, 250 community adults) and the control group (81 children, 133 community adults). Chi-square and Fisher's Exact tests were used to analyse differences in knowledge, practices, and parasite prevalence between pre- and post-intervention.ResultsAfter the intervention, the misperception that malaria has multiple causes was significantly improved, both among children and community adults. Moreover, the community adults who treated a bed net with insecticide in the past six months, increased from 21.5% to 50.0% (p < 0.001). Parasite prevalence in school children decreased from 30.9% to 10.3% (p = 0.003). These positive changes were observed only in the intervention group.ConclusionsThis study suggests that the participatory health education intervention contributed to the decreased malaria prevalence among children. It had a positive impact not only on school children, but also on community adults, through the improvement of knowledge and practices. This strategy can be applied as a complementary approach to existing malaria control strategies in West African countries where school health management systems have been strengthened.
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