Nucleosomes in gene regulation: theoretical approaches

This work reviews current theoretical approaches of biophysics and bioinformatics for the description of nucleosome arrangements in chromatin and transcription factor binding to nucleosomal organized DNA. The role of nucleosomes in gene regulation is discussed from molecular-mechanistic and biological point of view. In addition to classical problems of this field, actual questions of epigenetic regulation are discussed. The authors selected for discussion what seem to be the most interesting concepts and hypotheses. Mathematical approaches are described in a simplified language to attract attention to the most important directions of this field

Objectively measured physical activity in four-year-old British children: a cross-sectional analysis of activity patterns segmented across the day

Background: little is known about preschool-aged children’s levels of physical activity (PA) over the course of the day. Using time-stamped data, we describe the levels and patterns of PA in a population-based sample of four-year-old British children.Methods: within the Southampton Women’s Survey the PA levels of 593 4-year-old children (51% female) were measured using (Actiheart) accelerometry for up to 7 days. Three outcome measures: minutes spent sedentary (<20 cpm); in light (LPA: ?20 – 399 cpm) and in moderate-to-vigorous activity (MVPA: ?400 cpm) were derived. Average daily activity levels were calculated and then segmented across the day (morning, afternoon and evening). MVPA was log-transformed. Two-level random intercept models were used to analyse associations between activity level and temporal and demographic factors.Results: children were active for 67% (mean 568.5 SD 79.5 minutes) of their daily registered time on average, with 88% of active time spent in LPA. All children met current UK guidelines of 180 minutes of daily activity. There were no differences in children’s average daily levels of sedentary activity and LPA by temporal and demographic factors: differences did emerge when activity was segmented across the day. Sex differences were largest in the morning, with girls being more sedentary, spending fewer minutes in LPA and 18% less time in MVPA than boys. Children were more sedentary and less active (LPA and MVPA) in the morning if they attended childcare full-time compared to part-time, and on weekend mornings compared to weekdays. The reverse was true for weekend afternoons and evenings. Children with more educated mothers were less active in the evenings. Children were less sedentary and did more MVPA on summer evenings compared to winter evenings.Conclusions: preschool-aged children meet current physical activity guidelines, but with the majority of their active time spent in LPA, investigation of the importance of activity intensity in younger children is needed. Activity levels over the day differed by demographic and temporal factors, highlighting the need to consider temporality in future interventions. Increasing girls’ morning activity and providing opportunities for daytime activity in winter months may be worthwhil

Arene-perfluoroarene interactions in crystal engineering 8: structures of 1 : 1 complexes of hexafluorobenzene with fused-ring polyaromatic hydrocarbons

A series of 1:1 complexes of hexafluorobenzene (HFB) with naphthalene, anthracene, phenanthrene, pyrene and triphenylene were prepared and their X-ray crystal structures determined at low temperatures. Each structure contains infinite mixed stacks of alternating nearly-parallel molecules of HFB and arene, which display various slip distortions and form different 3-dimensional motifs. The naphthalene, anthracene and pyrene complexes show polymorphism. Crystal packing of HFB complexes is compared with that of corresponding octafluoronaphthalene complexes. Ab initio DFT calculations on the infinite lattices give lattice parameters and slip parameters in close agreement with the experimental crystal structures, while showing that intermolecular cohesion is predominantly of electrostatic, rather than van der Waals, origin

Arene-perfluoroarene interactions in crystal engineering: structural preferences in polyfluorinated tolans

The compounds 4-ROC6F4C[triple bond, length as m-dash]CPh (4) where R = Me (a), Et (b), Prn (c), Pri (d), Bun (e), n-C5H11 (f), PhCH2 (g), PhCH2CH2 (h), 4-MeC6H4 (i), 4-EtC6H4 (j) and menthyl (k), have been prepared by reaction of C6F5C[triple bond, length as m-dash]CPh (3) with ROH in the presence of KOH, and characterised by NMR (1H, 13C, 19F) and mass spectroscopy. The single-crystal structures of PhC[triple bond, length as m-dash]CPh·C6F5C[triple bond, length as m-dash]CC6F5 (1∶2), 3 and 4a,c,d,f,g,i have been determined by X-ray diffraction at 120–160 K, and that of 3 also calculated by an ab initio pseudo-potential DFT method. The tolan moiety is nearly planar in each molecule except 4a, which has a Ph/C6F5 dihedral angle of 25.8°. The R group adopts an out-of-plane orientation except in 4f, where the n-pentyl chain is nearly coplanar with the C6F5 group at the cost of severe distortion of the C(ar)–C(ar)–O angles (which differ by 13.5°). The structures of 1∶2, 3 (pseudo-isomorphous with 1∶2), 4a, 4g (disordered) and 4i contain stacks of alternating arene and perfluoroarene moieties; 4c and 4d form discrete centrosymmetric dimers with arene/perfluoroarene overlap, while 4f forms infinite stacks without such overlap. Differential thermal analysis and transmitted polarised light microscopy revealed no liquid-crystalline behaviour of 3 and 4

Recovery of polluted ecosystems: the case for long-term studies

Recovery of marine ecosystems from pollution has tended to receive less attention than the study of new or continuing impacts, but such studies are important in charting recovery from acute incidents and following legislation to deal with chronic contamination. Recovery is inevitably a long-term process, and where such studies have been made they are often too short-lived. Interest quickly wanes following an acute incident and governmental bodies rapidly switch to new legislative priorities for chronic inputs. We review three case studies: recovery of dogwhelk populations after local extinction by tributyl tin leachates from antifouling paints; recovery of rocky shore communities from oil spills; and recovery of estuarine ecosystems from industrial and urban development. We then make some generalisations about recovery processes before making a plea for long-term studies of polluted areas

Gas Atomization of Amorphous Aluminum: Part I. Thermal Behavior Calculations

In this article, the thermal history and cooling rate experienced by gas-atomized Al-based amorphous powders were studied via numerical simulations. Modeling simulations were based on the assumption of Newtonian cooling with forced convection, as well as an energy balance, which involves gas dynamics, droplet dynamics, and heat transfer between gas and droplet. To render the problem tractable, phase transformations, crystal nucleation, and growth were not taken into account in the analysis of the solidification of Al droplets; instead, an energy balance approach was formulated and used. The numerical results and associated analysis were used to optimize processing parameters during gas atomization of Al-based amorphous powder. The results showed that the cooling rate of droplets increases with decreasing powder size and can reach in excess of 105 K/s for powder <20 μm in diameter. Gas composition has a more significant influence on cooling rate than gas pressure, and 100 pct He has the highest cooling effect. The results also showed that the cooling rate increases with increasing melt superheat temperature