3,3'-Bis(acylamino)-2,2'-bipyridine discotics : desymmetrization and functionalization

In the field of supramolecular chemistry control over self-assembly is one of the main targets. This might be accomplished by adaptation of the environment of organic assemblies by allowing their interaction with other molecules or substrates. To do so, the assembling component has to be equipped with a functional site, which requires derivatization. Also, derivatization in itself may result in enhanced, beneficial supramolecular behavior. In this thesis, derivatization of disc-shaped molecules at their periphery is described with the goal of introducing functionality into the discotic systems and of allowing the discotics to perform desirable, programmed interactions with other molecules. The discotics are composed of a central trimesic core and radially equipped with three 2,2'-bipyridinyl-3,3'-diamine moieties that in turn are linked to three gallic moieties decorated with peripheral alkyl tails. In Chapter 1 an overview of functionalized and desymmetrized discotics is given, with the focus on single-core discotics like triphenylenes, hexabenzocoronenes, phthalocyanines, porphyrins and benzene-1,3,5-tricarboxamides. The synthesis of the desymmetrized derivatives as well as their enhanced supramolecular and material properties is described. It is clear that desymmetrization and functionalization of the originally symmetrical discotics allows programmed interaction with other molecules or gives rise to functional materials besides the original focus on one-dimensional assembly and columnar liquid crystals. In Chapter 2, two synthetic strategies to replace one of the 3,4,5-trialkoxyphenyl units of bis(acylamino)-2,2'-bipyridine based discotics with a phenyl (disc 1, Figure 1) or 4-pyridyl (disc 2, Figure 1) unit are proposed. The first synthetic strategy is based on a statistical approach and the second one on a step-wise approach involving protective-group chemistry. Both strategies have afforded the desired non-symmetrical discotics but the second strategy has many advantages over the first one, like easier purification steps and accessibility to multigram amounts of the desired discs and their valuable precursors. Importantly, the desymmetrization does not affect significantly the preorganized hydrogen-bonded structure of the discotics. The self-assembly properties of non-symmetrical discotics 1 and 2 are reported in Chapter 3. Both discotics display helical self-assembly in the mesophase and in apolar solution. Importantly, this assembly of discs 2 is similar to that of their C3-symmetical analogues showing that desymmetrization and functio-nalization of the discotics is feasible without undoing their self-assembly capabilities. In Chapter 4, the interaction of disc 2, possessing a peripheral 4-pyridyl group, with chiral acids is described as well as the supramolecular transfer of chirality. First several acids had to be screened to reveal which acids bind selectively with the discotic without disrupting its supramolecular properties. Apparently, acids of intermediate strength like phosphonic and tartaric acids satisfy this requirement. The appropriate chiral acids have then been used to induce chirality into the helical assemblies of disc 2 in solution. Apparently, the efficiency of the transfer of chirality is not only determined by the strength of the chiral acid, but also by steric effects. The stability of the chiral complex is highly sensitive and depends on the helix stability, the strength of the acid-base complex, and the solubility of the components. Chapter 5 deals with the incorporation of a functionalized discotic in methacrylate based polymers. Desymmetrized discotic 3 (Figure 1) carrying a dangling hydroxy group is synthesized that may act as a starting point for a wide variety of functionalized discotics. This is illustrated by transforming disc 1 into a polymerizable disc carrying a methacrylate group. This disc is then copolymerized under ATRP conditions to afford a disc-functionalized poly(butyl methacrylate) copolymer. The latter may serve as a novel material for supramolecular, fluorescent polymeric nanoparticles. In Chapter 6, a novel C3-symmetrical, heavily fluorinated disc 4 (Figure 1) is introduced. Replacing the originally hydrophobic hydrocarbon periphery by a fluorophilic fluorocarbon periphery (disc 4, Figure 1) allows helical self-assembly in fluorinated media. Teflon star 4 forms very stable columnar mesophases in which helicity may be present. Surprisingly, a proper choice of solvent combination allows the formation of mixed assemblies in which discotics possessing both a chiral, hydrocarbon periphery and fluorinated discotics 4 are present. This allows transfer of chirality from the former to the latter with the expression of amplification of chirality. Figure 1: Discotics described in this thesis. Non-symmetrical discotics 1 and 2 figure as the main topics in Chapters 2, 3 and 4. Hydroxy-disc 3 is applied in Chapter 5 and teflon disc 4 is the key molecule in Chapter 6

Do Traumatic Events Have More Impact on the Development of Dental Anxiety Than Negative, Non-traumatic Events?

The importance of exposure to traumatic events for the development of dental anxiety has not been investigated. The aim of the present study was to test the hypotheses that individuals who reported having been exposed to a traumatic event [that is, fulfilling Criterion A of the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5), for post-traumatic stress disorder (PTSD)] as the cause of their dental anxiety would report significantly higher levels of dental anxiety, typical trauma-related (PTSD) symptoms, and greater disturbance of memories involving these events than those who reported being exposed to non-traumatic events. Patients of a specialized dental fear clinic (n = 90) were divided into those who reported a traumatic event that initiated their dental trait anxiety and those who did not. The two groups did not differ in their severity of dental anxiety and number of PTSD symptoms, but the memories of those who had been exposed to traumatic events were significantly more vivid than the memories of those in the reference group. Length of time since the event took place did not play a role. Hence, traumatic events are remembered more vividly, but do not seem to initiate more severe forms of dental anxiety than other events

Disease burden of extreme treatment anxiety; quality of life for patients with and without extreme dental treatment anxiety

In this study, a comparison was made between disease-specific (oral health-related) quality of life (OHQoL), measured with the OHIP-14 questionnaire, and generic (general health-related) quality of life (GHQoL), measured with the EQ5D-5L questionnaire, in patients with and without extreme dental treatment anxiety. A total of 76 patients who could not be treated due to extreme dental treatment anxiety were referred to a centre for special dentistry. These patients were matched, according to age, gender and socioeconomic status, with participants in an epidemiological study on oral health (n = 1125). Wilcoxon signed-rank tests were used on both groups to compare GHQoL and OHQoL. The total OHIP score was higher (representing a lower quality of life) in the patient group than in the control group. Anxiety patients scored higher on all 7 domains of the OHIP-14. With respect to general quality of life, patients with extreme treatment anxiety were found to report lower utility scores than the matched control group. With these results, a total disease burden of 74,000 disability-adjusted life years (DALYs) was calculated for extreme treatment anxiety in the Netherlands. The findings of this study reveal that having extreme dental treatment anxiety results in a significant disease burden in the Netherlands.</p

Caries in deprived areas 1. Adults

In the Netherlands, little epidemiologic data is available on the oral health of the various cultural groups comprising the adult population living in deprived areas. The aim of an investigation carried out in 2013 was to obtain an impression of the extent of caries experience among less well-educated adults in deprived areas by comparison with a reference group of adults from the city of 's-Hertogenbosch. A total of 1,597 less well-educated respondents participated in this research. The reference population had the largest amount of caries experience, mostly due to a relatively large number of filled surfaces. The relatively low caries experience found in the respondents in the deprived areas with a non-Dutch cultural affiliation was due to lower numbers of filled surfaces. The differences in average filled-surface scores were statistically significant in all age categories, except the youngest. The strategy of 'extension for prevention' in caries treatment in the permanent dentition represents a possible explanation for the fact that less well-educated adults in 's-Hertogenbosch had significantly more filled surfaces than those with a non-Dutch cultural affiliation.</p

Formation of Columnar Liquid Crystals on the Basis of Unconventional Triazine-Based Dendrimers by the C3-Symmetric Approach

[[abstract]]Two series of unconventional triazine-based dendrimers with C2 symmetry and C3 symmetry were prepared. The newly prepared C3-symmetrical dendrimers were characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Differential scanning calorimetry, polarizing microscopy, and powder XRD showed that the C3-symmetrical dendrimers display columnar liquid-crystalline phases during thermal treatment, but the C2-symmetrical dendrimers were not observed to behave correspondingly. The molecular conformations of C3- and C2-symmetrical dendrimers were obtained by computer simulation with the MM2 model of the CaChe program in the gas phase. The simulation results reasonably explain the different mesogenicities of C3- and C2-symmetric dendrimers. This new strategy should be applicable to other types of unconventional dendrimers with rigid frameworks for displaying columnar liquid-crystalline behavior.[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]紙本[[countrycodes]]DE

Tribology studies of the natural knee using an animal model in a new whole joint natural knee simulator

The successful development of early-stage cartilage and meniscus repair interventions in the knee requires biomechanical and biotribological understanding of the design of the therapeutic interventions and their tribological function in the natural joint. The aim of this study was to develop and validate a porcine knee model using a whole joint knee simulator for investigation of the tribological function and biomechanical properties of the natural knee, which could then be used to pre-clinically assess the tribological performance of cartilage and meniscal repair interventions prior to in vivo studies. The tribological performance of standard artificial bearings in terms of anterior–posterior (A/P) shear force was determined in a newly developed six degrees of freedom tribological joint simulator. The porcine knee model was then developed and the tribological properties in terms of shear force measurements were determined for the first time for three levels of biomechanical constraints including A/P constrained, spring force semi-constrained and A/P unconstrained conditions. The shear force measurements showed higher values under the A/P constrained condition (predominantly sliding motion) compared to the A/P unconstrained condition (predominantly rolling motion). This indicated that the shear force simulation model was able to differentiate between tribological behaviours when the femoral and tibial bearing was constrained to slide or/and roll. Therefore, this porcine knee model showed the potential capability to investigate the effect of knee structural, biomechanical and kinematic changes, as well as different cartilage substitution therapies on the tribological function of natural knee joints

Induction of the Columnar Phase of Unconventional Dendrimers by Breaking the C2 Symmetry of Molecules

[[abstract]]Two triazine-based unconventional dendrimers were prepared and characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Differential scanning calorimetry, polarizing microscopy, and powder XRD studies showed that these dendrimers display columnar liquid-crystalline phases during thermal treatment. This is ascribable to breaking of their C2 symmetry. The molecular conformations of prepared dendrimers were obtained by computer simulation with the MM3 model of the CaChe program in the gas phase. The simulation showed that the conformations of the prepared dendrimers are rather flat and disfavor formation of the LC phase. However, due to C2-symmetry breaking, the prepared dendrimers have structural isomers in the solid state and thus show the desired columnar phases. This new strategy should be applicable to other types of unconventional dendrimers with rigid frameworks.[[journaltype]]國外[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]電子版[[booktype]]紙本[[countrycodes]]DE