Effects of strand and directional asymmetry on base-base coupling and charge transfer in double-helical DNA

Mechanistic models of charge transfer (CT) in macromolecules often focus on CT energetics and distance as the chief parameters governing CT rates and efficiencies. However, in DNA, features unique to the DNA molecule, in particular, the structure and dynamics of the DNA base stack, also have a dramatic impact on CT. Here we probe the influence of subtle structural variations on base-base CT within a DNA duplex by examining photoinduced quenching of 2-aminopurine (Ap) as a result of hole transfer (HT) to guanine (G). Photoexcited Ap is used as a dual reporter of variations in base stacking and CT efficiency. Significantly, the unique features of DNA, including the strandedness and directional asymmetry of the double helix, play a defining role in CT efficiency. For an (AT)(n) bridge, the orientation of the base pairs is critical; the yield of intrastrand HT is markedly higher through (A)n compared with (T)(n) bridges, whereas HT via intrastrand pathways is more efficient than through interstrand pathways. Remarkably, for reactions through the same DNA bridge, over the same distance, and with the same driving force, HT from photoexcited Ap to G in the 5' to 3' direction is more efficient and less dependent on distance than HT from 3' to 5'. We attribute these differences in HT efficiency to variations in base-base coupling within the DNA assemblies. Thus base-base coupling is a critical parameter in DNA CT and strongly depends on subtle structural nuances of duplex DNA

Superorbital Period in the High Mass X-ray Binary 2S 0114+650

We report the detection of a superorbital period in the high-mass X-ray binary 2S 0114+650. Analyses of data from the Rossi X-ray Timing Explorer (RXTE) All-Sky Monitor (ASM) from 1996 January 5 to 2004 August 25 reveal a superorbital period of 30.7 +/- 0.1 d, in addition to confirming the previously reported neutron star spin period of 2.7 h and the binary orbital period of 11.6 d. It is unclear if the superorbital period can be ascribed to the precession of a warped accretion disc in the system.Comment: 5 pages, 5 figures, submitted to MNRAS 27th January 2005. Manuscript expanded to include discussion of evolution of periods, and hardness ratio variability. Number of figures increased from 5 to 9. Accepted for publication 19th December 200

A Multicoloured View of 2S 0114+650

We report the results of radio and X-ray observations of the high mass X-ray binary 2S 0114+650, made with the Giant Meterwave Radio Telescope and the Rossi X-ray Timing Explorer respectively. No emission was detected at radio wavelengths. The neutral hydrogen column density was found to vary over the orbital period, while no variability over the the super-orbital period was observed. We discuss the causes of the observed relationships and the implications for the underlying mechanisms.Comment: 4 pages, 2 figures; to appear in proceedings for "The multicoloured landscape of compact objects and their explosive progenitors", Cefalu, Sicily, 2006 June 11-24, AIP, submitte

Recurrent ~24 h Periods in RXTE ASM Data

Analysis of data from the Rossi X-ray Timing Explorer satellite's All Sky Monitor instrument for several X-ray binary sources has identified a recurrent \~24 h period. This period is sometimes highly significant, giving rise to the possibility of it being identified as an orbital or super-orbital period. Further analysis has revealed the same period in a number of other X-ray sources. As a result this period has been discounted as spurious, described variously as arising from daily variations in background levels and beating between the sampling period and long-term secular trends in the light curves. We present here an analysis of the spurious periods and show that the dominant mechanism is in fact spectral leakage of low-frequency power present in the light curves.Comment: 9 Pages, 10 figures, 1 table, submitted to PASA 20th December 2004. Added 1 page of text and 3 figures to clarify results and discussion. Resubmitted 16th May 2005. Accepted 25th June 200

Using creative writing to explore facilitation skills in practice

Background: Facilitation skills are key to the effective use of practice development strategies. Students on a Masters in Practice Development and Innovation undertake a module on Facilitation skills which incorporates the use of a creative writing piece to explore facilitation. The aim of this article is to critically reflect on the use of creative writing within an assignment from the lecturer perspective. Critical Reflection: Rolfe et al (2001) model of reflection will be utilised to structure the reflections, considering the questions ‘What?’, ‘So What?’ and ‘Now What?’. This will discuss the concerns about the assessment method, student thoughts, relationship to practice development and evidence of effectiveness of the strategy. Examples of creative writing from the students will be used to demonstrate the diversity of the approach. Ethics: All students have given permission for their work to be included Discussion: Using creative writing can be freeing for students as they can use their voice to explore a topic. For the lecturer courage is needed to facilitate this expression but is rewarding as links to the principles of practice development to embed new ways of working. Important within the process is the need to give students ‘permission’ to utilise a non-traditional style of writing and the lecturer may benefit from practising the technique themselves to feel comfortable with the creative writing strategy. Conclusion: Creative writing enabled an opportunity to explore facilitation in different ways and relate to different aspects of real and imagined life. This paper shows that creative writing can be used successfully by students to engage in novel ways of thinking. However, future actions identify the importance of guidance regarding relevance to academia and ensuring the lecturer is familiar with the aim and techniques of the process when using it for Masters level assessment

DNA Charge Transport: Conformationally Gated Hopping through Stacked Domains

The role of base motions in delocalization and propagation of charge through double helical DNA must be established experimentally and incorporated into mechanistic descriptions of DNA-mediated charge transport (CT). Here, we address these fundamental issues by examining the temperature dependence of the yield of CT between photoexcited 2-aminopurine (Ap*) and G through DNA bridges of varied length and sequence. DNA assemblies (35-mers) were constructed containing adenine bridges Ap(A)_nG (n = 0−9, 3.4−34 Å) and mixed bridges, ApAAIAG and ApATATG. CT was monitored through fluorescence quenching of Ap* by G and through HPLC analysis of photolyzed DNA assemblies containing Ap and the modified guanine, N_2-cyclopropylguanosine (^(CP)G); upon oxidation, the ^(CP)G radical cation undergoes rapid ring opening. First, we find that below the duplex melting temperature (∼60 °C), the yield of CT through duplex DNA increases with increasing temperature governed by the length and sequence of the DNA bridge. Second, the distance dependence of CT is regulated by temperature; enhanced DNA base fluctuations within duplex DNA extend CT to significantly longer distances, here up to 34 Å in <10 ns. Third, at all temperatures the yield of CT does not exhibit a simple distance dependence; an oscillatory component, with a period of ∼4−5 base pairs, is evident. These data cannot be rationalized by superexchange, hopping of a localized charge injected into the DNA bridge, a temperature-induced transition from superexchange to thermally induced hopping, or by phonon-assisted polaron hopping. Instead, we propose that CT occurs within DNA assemblies possessing specific, well-coupled conformations of the DNA bases, CT-active domains, accessed through base motion. CT through DNA is described as conformationally gated hopping among stacked domains. Enhanced DNA base motions lead to longer range CT with a complex distance dependence that reflects the roles of coherent dynamics and charge delocalization through transient domains. Consequently, DNA CT is not a simple function of distance but is intimately related to the dynamical structure of the DNA bridge

Longevity and mortality in Kennel Club registered dog breeds in the UK in 2014

Abstract Background The domestic dog is one of the most diverse mammalian species, exhibiting wide variations in morphology, behaviour and morbidity across breeds. Therefore, it is not unexpected that breeds should also exhibit variation in mortality and longevity. While shorter longevity per se may not necessarily be a welfare issue, a generally foreshortened lifespan in a breed that is accompanied by a high prevalence of a particular cause of death may reveal potentially serious welfare concerns and highlight scope to improve breed welfare. Survey data gathered directly from owners offer useful insights into canine longevity and mortality that can support the overall evidence base for welfare reforms within breeds. Results Mortality data on 5663 deceased dogs registered with the UK Kennel Club were collected from an owner-based survey. The most commonly reported causes of death were old age (13.8%), unspecified cancer (8.7%) and heart failure (4.9%); with 5.1% of deaths reported as unknown cause. Overall median age at death was 10.33 years (interquartile range: 7.17–12.83 years). Breeds varied widely in median longevity overall from the West Highland Terrier (12.71 years) to the Dobermann Pinscher (7.67 years). There was also wide variation in the prevalence of some common causes of death among breeds, and in median longevity across the causes of death. Conclusion Substantial variation in the median lifespan and the prominent causes of death exists across breeds. This study has identified some breeds with both a low median lifespan and also a high proportional mortality for one or more specific causes of death that should be considered as both potential welfare concerns as well as opportunities for improvement