49,463 research outputs found
Octyl-decorated Fréchet-type dendrons : a general motif for visualisation of static and dynamic behaviour using scanning tunnelling microscopy
No full textFirstly, a short overview on supramolecular chemistry including definitions, basic principles and examples taken from the literature of 2D and 3D self-assembly processes is given in Chapter 1. The introduction is completed by some general ideas of dendrimer chemistry. In the second Chapter the techniques used in this thesis are introduced with a special focus on scanning tunnelling microscopy (STM). Besides the mode of operation and the data processing, the historical background is briefly described. The following four Chapters present STM studies of monolayers formed by different types of compounds, all functionalised with Fréchet-type dendrons. Not only static features of monolayers such as conformational analysis of single molecules have been investigated, but also dynamic processes such as delayed conversion of a whole domain and conformational changes by protonation have been examined. The 2D properties of monolayers on a graphite surface have been compared with the X-ray data of 3D single crystals. For two compounds, the same molecular arrangement has been detected in monolayers on graphite and in single crystals. Together with organic molecules, the self-assembly of metal complexes possessing tpy ligands and organometallic species with platinum(II) bis(alkynyl) units has been examined. Not all of these metal complexes were stable under the scanning conditions used in STM. A synthetic programme leading to dendrimer-functionalised organic and organometallic compounds has been developed. Discussions of synthetic routes are given at the beginning of each Chapter. Chaptercompares X-ray diffraction methods with STM, the two main analysis tools used for investigation of self-organised assemblies in the solid state in this thesis. In the second part of Chapter 7, the results presented in the previous Chapters are discussed with some general reflections on the self-assembling properties of Fréchet-type dendrimers with pendant octyl groups. Additional to the studies of self-assembled monolayers, the formation of metallomacrocycles has been investigated using two novel homoditopic tpy ligands. This work is presented in Chapter 8. It was demonstrated that the ring-size depends on the metal used for the cyclisation. Furthermore, some of the macrocycles formed self-assembled monolayers on graphite, which have been examined using STM. One homoditopic ligand formed a molecular square by complexation with an iron(II) salt which was analysed using single crystal X-ray diffraction. This thesis has brought together the realms of chemical design with studies of the physical behaviour of the envisioned molecules on the surface. It has been demonstrated that Fréchet-type dendrimers with octyl end-groups are a general motif for visualisation of static and dynamic behaviour using STM
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
From self assembled monolayers to clickable gold nanoparticles
No full textThe aim of the present PhD thesis was the investigation of the behavior of gold nanoparticle stabilizing oligo thioether ligands on gold surfaces and further on to develop a protocol for the directed assembly of mono functionalized gold nanoparticle into defined oligomer structures.
Outline
The present cumulative PhD thesis consists of the following parts:
In the Introduction the research field of gold nanoparticles is presented with to point out their unique electronic and physical properties. The second focus will be on the controlled interlinking and functionalization of gold nanoparticles using click chemistry and their potential applications, which will be submitted as a review article.
Within Concept and Strategy the goals of the research project are introduced and the concepts and outputs of the resulting publications are presented.
The Publications are accumulated with their respective Supporting Information, in the order in which they were prepared:
“Loops versus Stems: Benzylic Sulfide Oligomers Forming Carpet Type Monolayers“ F. Sander, T. Peterle, N. Ballav, F. Wrochem, M. Zharnikov, M. Mayor J. Phys. Chem. C, 2010, 114, 4118 – 4125.
“Add a Third Hook: S-Acetyl Protected Oligophenylene Pyridine Dithiols as Advanced Precursors for Self-Assembled Monolayers“ F. Sander, J. P. Hermes, M. Mayor, H. Hamoudi, M. Zharnikov PCCP, 2013, 15, 2836 – 2846.
“Dumbbells, Trikes and Quads - Click Gold Nanopartricles together“ F. Sander, U. Fluch, J. P. Hermes and M. Mayor Small 2014, 10, 349 – 359.
“Click Chemistry with Gold Nanoparticles – A Tool for Functionalization, Interlinking and Labeling” Fabian Sander and Marcel Mayor, manuscript prepared for submission.
Finally, within Conclusion and Outlook the main results are briefly summarized and further potential research is proposed
Extracting Boer-Mulders functions from p+D Drell-Yan processes
No full textWe extract the Boer- Mulders functions of valence and sea quarks in the proton from unpolarized p + D Drell- Yan data measured by the FNAL E866 Collaboration. Using these Boer- Mulders functions, we calculate the cos2 phi asymmetries in unpolarized pp Drell- Yan processes, both for the FNAL E866/ NuSea and the BNL Relativistic Heavy Ion Collider experiments. We also estimate the cos2 phi asymmetries in the unpolarized p (P) over bar Drell- Yan processes at GSI.Astronomy & AstrophysicsPhysics, Particles & FieldsSCI(E)37ARTICLE5null7
The experience of caring for someone with dementia: a biographical study
No full textThis research was about the lived experience of caring for someone with dementia. Six informal carers of people with dementia were interviewed. The carers were defined as ‘informal’ as they were family and friends, and therefore unpaid. Five of the carers were women who had or were supporting their mothers, and one was a man, who had cared for a friend. Three carers identified as lesbian or gay. I wanted to hear the stories of a group that are generally neglected in research (Turnball, 2002). Carers are diverse with a range of needs, and I wished to discover if services were ‘gay friendly’ or implicitly heterosexist. In addition I wanted lesbian and gay carers’ stories to be heard and their contribution to be recognised. The research is important as there are an estimated 750,000 people living with dementia in the UK and 500,000 partners, family members and friends are involved in caring for someone with dementia at a value of £6 billion a year, if care was provided by health and social care services (Department of Health, 2009). The research method was biographical in relation to the participants’ caring role. It explored three areas: the experience of caring, coping approaches and encounters with health and social care services. The interviews with carers took place in 2010 and the cared for had, or were living in: London, Wales, south-east and north-west England. The theoretical perspective of the research was person centred (Kitwood, 1997) set within the legislative and social policy framework for carers. The data was analysed primarily through pre-determined codes arising from the interview schedule and Skills for Care ‘Core Principles for Carers’ (2010) but also searching for patterns within and across cases. The findings were that the carers did not experience the person with dementia as a burden, but contact with health and social services was often problematic due to the fragmentation of services, lack of one practitioner co-ordinating care, and an absence of knowledge about carers’ legal entitlements. In addition services adopted a medical model of care focusing on the dementia of the cared for with limited interest in the cared for or carer’s biography, consequently services were not person centred, or gay friendly. Carers’ commitment to the person with dementia was on a continuum between the obligations of kinship and unconditional love. Positive aspects in the relationships endured in particular humour and shared activities. The messages for practice were that health and social care practitioners require training in person centred practice, as well as the legislation and policy framework for carers. Personalisation of services provides opportunities for shifting services from a task centred to person centred approach, including the development of gay friendly services?<br/
Use of formalin-fixed tissues to determine fumonisin B1-induced sphingolipid alterations in swine
No full text
Part I: Characterization of Cr3C2-25% NiCr reactive plasma sprayed coatings produced at different pressures
No full textThe present work was performed with the aim of characterizing various plasma sprayed Cr3C2-NiCr coatings produced by using different processing pressures between 300 and 1200 mbars, in a nitrogen controlled atmosphere CAPS system. X-Ray diffraction was carried out on all coatings by using Bragg-Brentano geometry. The phases identified in the as-supplied powder Cr3C2/Ni-Cr were fcc Ni-Cr and orthorhombic Cr3C2. In contrast to the original powder, the coatings showed evidence of Cr3C2, Ni-Cr and either Cr6.2C3.5N0.3 or Cr3C1.52N0.48 carbo-nitride phases depending on the ratio of C/N in the coating. The presence of Cr7C3 and CrO2 was also identified in the coatings deposited at atmospheric pressure. The volume fraction of carbide plus nitride phase in the coating was always less than the volume fractions of the carbide phase in the original feed stock powder. The volume fraction of carbide plus nitride phase was found to depend quite markedly on the spraying parameters such as pressure, power input, spraying distance and substrate cooling. The results have been presented in terms of spraying efficiency, ξ. The highest value of ξ (86.4%) was obtained for coatings produced at 1200 mbar pressure, a spraying distance of 120 mm, without N2 cooling and the lowest value (25.2%) was found for the coatings deposited at 300 mbar for the same spraying distance but with N2 cooling. The presence of graphitic carbon was detected in all samples especially for specimens where the fraction of carbide plus carbo-nitride phases was the greatest. The influence of spraying parameters such as pressure, power input, spraying distance and substrate cooling on the microstructure was determined. The highest microhardness value of 2296 HV50 was found for the carbide plus carbo-nitride phase contained in the specimens produced at 1200 mbar spraying pressure, 120-mm spraying distance and substrate heating at 600°C. © 2001 Elsevier Science B.V. All rights reserved
The independent and interactive associations of physical activity intensity and vitamin D status with bone mineral density in prepubertal children: the PANIC Study
No full textSummary
It is unclear how physical activity intensity and vitamin D status are related to bone health in prepubertal children. We found positive associations between vitamin D status and moderate-to-vigorous physical activity with bone in boys and girls. This highlights the importance of lifestyle factors for skeletal health prepuberty.
Introduction
The sex-specific independent and interactive associations of physical activity (PA) intensity and serum 25-hydroxyvitamin D (25(OH)D) levels with areal bone mineral density (aBMD) were investigated in prepubertal children.
Methods
The participants were 366 prepubertal Finnish children (190 boys, 176 girls) aged 6–8 years. Linear regression analysed the associations of sedentary time (ST), light PA (LPA), moderate PA (MPA), moderate-to-vigorous PA (MVPA) and vigorous PA (VPA) measured by accelerometery, and serum 25(OH)D with total body less head (TBLH) and lower-limb aBMD, measured by dual-energy X-ray absorptiometry.
Results
There was no interaction between PA intensity or serum 25(OH)D and sex with aBMD. MPA and MVPA were positively associated with TBLH and lower-limb aBMD (β = 0.11, 95% CI 0.02–0.20, p = 0.01). Serum 25(OH)D was positively associated with TBLH and lower-limb aBMD (β = 0.09, 95% CI 0.01–0.18, p = 0.03). There were no interactions between PA intensity and serum 25(OH)D with aBMD.
Conclusion
Vitamin D status, MPA and MVPA levels in active prepubertal children were positively associated with aBMD. The influence of MVPA is due to the MPA component, though our findings regarding the role of VPA should be interpreted with caution, as shorter accelerometer epochs are needed to more accurately assess VPA. This study adds evidence to the promotion of MPA and behaviours to encourage optimal vitamin D status in supporting skeletal health in childhood, though these need not be used in conjunction to be beneficial, and a sex-specific approach is not necessary in prepubertal children.
Trial registration number
NCT01803776. Date of registration: 4/03/2013Peer reviewedFinal article publishedAccelerometeryGrowth failureDXAChildhoodBone mas
How structural factors influence the performance of copper(I) bis(diimine) based DSCs
No full textAbstract
This PhD thesis is based on the synthesis of new homoleptic copper(I) complexes and their applications in dye-sensitized-solar-cells (DSCs).
Chapter I: Is an evaluation of the anchoring ligands effect upon device performance containing ancillary ligands of 1st and 2nd generation hole transport triphenylamino-dendrons.
Chapter II: Describes the influence of six different substituents in the 6,6’-positions of the ancillary ligands on the device performance.
Chapter III: Is a short study of a more atom economic device assembling method, where the copper(I) complex is formed in situ on the TiO2 surface.
Chapter IV: Shows the influence of the dye conentration used during the dyeing process of the semi-conductor.
Chapter V: Is a study of how the enhanced photon absorption, achieved by extending the aromatic system of the ancillary ligand, affects the cell performance.
Chapter VI: Describes the use of different solvents during the dyeing process of the photoanode and their influence on DSC performance.
Chapter VII: Addresses issues concerning the TiO2 surface such as the aggregation of dye molecules and how the addition of co-adsorbants during the dyeing cycle may prohibit the formation of such aggregates.
Parts of this work have been published:
• B. Bozic-Weber, S. Y. Brauchli, E. C. Constable, S. O. Fürer, C. E. Housecroft and I. A. Wright, Phys. Chem. Chem. Phys., 2013, 13, 4500-4504.
• B. Bozic-Weber, S. Y. Brauchli, E. C. Constable, S. O. Fürer, C. E. Housecroft, F. J. Malzner, I. A.Wright and J. A. Zampese, Dalton Trans., 2013, 34, 12293-12308.
• S. Y. Brauchli, B. Bozic-Weber, E. C. Constable, N. Hostettler, C. E. Housecroft and J. A. Zampese, RSC Advances, 2014, 4, 34801-34815.
• S. Y. Brauchli, F. J. Malzner, E. C. Constable and C. E. Housecroft, RSC Advances, 2014, 4, 62728-62736.
• S. Y. Brauchli, E. C. Constable, C. E. Housecroft, Dyes and Pigments, 2015, 113, 447-450.
Summary
Within this study, 18 ligands (L1.1-L3.6) and their homoleptic copper(I) complexes [Cu(L1.1-L3.6)2][PF6] have been synthesized. They were fully characterized by 1H and 13C NMR, mass spectrometry, solution absorption spectrometry, melting point, elemental analysis and infrared spectrometry. Furthermore, all homoleptic Cu(I) complexes were electrochemically analysed by cyclic voltammetry and square-wave voltammetry.
By increasing the aromatic system in the ligands (Scheme 26), the light harvesting was effectively enhanced (e.g. going from L1.1 -> L2.1 -> L3.1). An increase in absorption by extending the aryl system was achieved in the homoleptic Cu(I) complexes, with an extinction of about twice that the free ligands.
Scheme 26: Representative ligands to illustrate the extension of the aryl system.
Furthermore, the substituents in the 6,6´-positions on the bipyridine were varied within each ligand generation (Scheme 26). All complexes were incorporated in DSCs.
In Chapter I, the first focus is on the influence of the anchoring ligand on the performance of a DSC. For this study, two representative capping ligands were introduced by treating an anchoring ligand covered photoanode with complexes [Cu(L2.1)2][PF6] and [Cu(L3.1)2][PF6]. By using these two example dyes, a set of four anchoring ligands was screened to identify the one that yielded the best conversion efficiency in the device.
Scheme 27: Set of anchoring ligands with phosphonic and carboxylic acids as anchoring groups.
It turned out that devices with anchoring ligands decorated with phosphonic acids (ALP and ALP1) generally achieve higher efficiencies than those with carboxylic acids (ALC and ALC1). Additionally, the influence of the extended aryl system on the ancillary ligands (L2.1 vs. L3.1) was examined in this set. Indeed, higher conversion efficiencies were obtained from devices incorporating the more conjugated ancillary ligand L3.1 compared to L2.1.
Scheme 28: Ancillary ligands L1.1-L1.6 examined in Chapter II.
In Chapter II, the influence of 6 different substituents in the 6,6’-positions of the bipyridine ancillary ligands (Scheme 28) in combination with anchoring ligands ALP and ALP1 was examined. It was found that DSCs incorporating anchoring ligands ALP1 reach much higher conversion efficiencies than those with ALP. Ancillary ligands L1.3 and L1.5 reached remarkably higher efficiencies, which was attributed to the reduced charge recombination rate.
Scheme 29: Two approaches to introduce a copper metal ion and an ancillary ligand on a TiO2 coated photoanode.
In Chapter III, a new strategy for incorporating heteroleptic complexes on the TiO2 surface was tested and compared with the state of the art methodology. The state of the art method works as followed. After an anchoring ligand has been adsorbed on a semiconductor surface, the photoanode is immersed in a solution of homoleptic Cu(I) complex. Due to the labile nature of Cu(I) complexes, a ligand exchange with the previously anchored ligand occurs, leaving with heteroleptic copper dye on the surface.
In the second methodology it becomes needless to prepare the homoleptic Cu(I) complex beforehand. By using the new method (stepwise methodology), an additional step during the dyeing process is required. Nevertheless, it is more economic than the conventional process. After the anchoring ligand is bound to the TiO2 surface, the anode is immersed in a solution of [Cu(MeCN)4][PF6]. At this stage the copper(I) binds to the anchoring ligand and it is assumed that a heteroleptic complex with two coordinating acetonitrile molecules is formed. In the last step, the anode with the intermediate heteroleptic complex on the surface is immersed in a solution of pure ligand, which replaces the acetonitrile molecules due to the chelating effect. The main outcome of this survey was that devices prepared by the state of the art method achieve a higher final conversion efficiency than those prepared from the stepwise assembly. However, using this new method, devices exhibited a higher initial efficiency than those prepared from the old method.
In Chapter IV, devices were prepared from four different concentrations of dye solutions ([Cu(L2.1)2][PF6] in CH2Cl2 at 2.0, 1.0, 0.5 and 0.1 mM). Their initial efficiencies and their development over several days were compared. The results showed that devices prepared from the least concentrated dye solutions reached their maximum efficiency immediately after assembling the cells and this efficiency was maintained over the whole measuring period. Additionally, it was found that DSCs prepared from the more dilute dye solutions reach a higher maximum conversion efficiency than those prepared from concentrated dye solutions.
In Chapter V, the focus was on the change in device performance by extending the aromatic systems of the ancillary ligands. Ligands L2.1-2.6 and L3.1-3.6 were introduced into the DSCs by applying the state of the art ligand exchange method using complexes [Cu(L2.1-2.6)2][PF6] and [Cu(L3.1-3.6)2][PF6]. Except for ancillary ligand L3.1, no increase in efficiency was recorded by extending the aromatic system and increasing the absorption. Although the solid state UV-vis absorption spectra of the photoanodes showed an increase in absorption intensity, no gain in Jsc was achieved.
Chapter VI addresses the use of two different solvents during the dyeing process of the photoanodes. The cells were prepared either from acetone or CH2Cl2 dye solutions of [Cu(L2.1-2.6)2][PF6] and [Cu(L3.1-3.6)2][PF6]. By measuring solid state absorption spectra of dye loaded photoanodes, it turned out that upon using acetone during the dyeing process a severe increase of dye adsorption on the TiO2 surface was achieved. Moreover, by using acetone dye solutions the devices incorporating the more conjugated ancillary ligands (L3.1-3.6) reach generally higher efficiencies than cells with ligands L2.1-L2.6. DSCs prepared from acetone dye solutions containing capping ligands L3.1-3.6 also exhibit higher efficiencies than those with the same ancillary ligands prepared from CH2Cl2 solutions. For devices with capping ligands L2.1-2.6, no clear trend could be discovered by comparing cells prepared from acetone and CH2Cl2 dye solutions.
In Chapter VII, the main attempt was to minimize the dye aggregation on the surface by adding a co-adsorbant (chenodeoxycholic acid) to the dye solution during the dyeing process of the photoanode. The homoleptic complexes [Cu(L3.1)2][PF6] and [Cu(L3.5)2][PF6] served as example dyes. Additionally, cells were prepared again from acetone and CH2Cl2 dye solutions. Interestingly, all devices prepared from CH2Cl2 in the presence of cheno showed a clear increase in efficiency compared to the control devices without co-adsorbant. Furthermore, the device with ancillary ligand L3.5 prepared from acetone dye solution with cheno showed a higher conversion efficiency than its control cell. The device with the capping ligand L3.1 obtained from an acetone dye solution with cheno did not show an increased performance.
Conclusion
It has been shown that by increasing the aromatic system of the ancillary ligand, a gain in absorption intensity and an increase in conversion efficiency was achieved under certain circumstances. The studies revealed the huge number of possible tuning sites of DSCs, such as structural properties of the dye, dye concentration and solvent used during the dyeing cycle, and aggregation issues concerning the molecular size of the dye. Nevertheless, this work showed that a dye that does not seem to yield a reasonable conversion efficiency at first might reveal its full potential after some time. Screening of dyes is quite delicate because it is simply impossible to know the optimal conditions for every dye and it is likely to miss a potentially good dye.
Outlook
For the future, one may want to think to test more solvents during the dyeing process of the photoanode in order to obtain even higher device performances. Additionally, it might be reasonable to add a co-adsorbant to all of the synthesized dyes during the dyeing process of the photoanode in order to reduce dye aggregation, reduce charge recombination and increase the efficiency. Furthermore, that it is also sensible to test new electrolytes in combination with these dyes in attempt to obtain, for example, a higher Voc
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