Consequences of cooperativity in supramolecular polymers

N,N',N"-Trialkylbenzene-1,3,5-tricarboxamides (BTAs) self-assemble by means of strong, threefold intermolecular hydrogen bonding into well-defined, helical, one-dimensional columnar aggregates.1 When a stereogenic centre is introduced into the alkyl side chains of these BTA molecules, strong Cotton effects are observed in dilute apolar solutions, indicating the preference for one helical conformation over the other.2 A helical sense preference can also be created by the introduction of isotope chirality into the a-position of the alkyl side chains in BTA molecules. Quantitative analysis on the observed process in dodecane demonstrates that a stereoselectively deuterated BTA forms right- (P) and left-handed (M) helical supramolecular polymers with a slight difference in stability upon cooling and the diastereomeric excess (d.e. = ([M]-[P])/([M]+[P])) is 38% at room temperature3. The subtle character of these deuterated-BTA-based supramolecular polymers makes it a highly sensitive probe to investigate the effect of the molecular structure of the alkane solvent in the self-assembly processes4. Furthermore, the effect of adding a racemization reaction into a self-assembly process by using a BTA molecule with a labile stereocenter was investigated. Racemization reaction in a self-assembling BTA system follows nonfirst-order reaction kinetics. Enantioenriched BTA molecules are obtained from a racemizing solution in the presence of a sergeant molecule which is unreactive towards base. The results are further analyzed by using a theoretical model which is capable of precise quantitative description of the experimental data obtained. The calculations are fully confirmed by experimental data with even the smallest details being fully explained by the methodology employed4. This dissertation focuses on the self-assembly process of BTA molecules and investigates the effect of isotope substitution, alkane solvent employed for self-assembly process and the introduction of racemization reaction into the self-assembly process. 1. A. R. A. Palmans, E. W. Meijer, Angew. Chem. Int. Ed. 2007, 46, 8948. 2. P. J. M. Stals, M. M. J. Smulders, R. Martin-Rapùn, A. R. A. Palmans, E. W. Meijer, Chem. Eur. J. 2009, 15, 2071. 3. S. Cantekin, D. W. R. Balkenende, M. M. J. Smulders, A. R. A. Palmans, E. W. Meijer, Nat. Chem. 2011, 3, 42. 4. S. Cantekin, Y. Nakano, J. C. Everts, P. van der Schoot, E. W. Meijer, A. R. A. Palmans, Chem. Commun. 2012, 48, 3803. 5. S. Cantekin, H. M. M. ten Eikelder, A. J. Markvoort, M. A. J. Veld, P. A. Korevaar, M. M. Green, A. R. A. Palmans and E. W. Meijer, Angew. Chem. Int. Ed. 2012 DOI 10.1002/anie.201201701

No short-cut in assessing trial quality: a case study

Assessing the quality of included trials is a central part of a systematic review. Many check-list type of instruments for doing this exist. Using a trial of antibiotic treatment for acute otitis media, Burke et al., BMJ, 1991, as the case study, this paper illustrates some limitations of the check-list approach to trial quality assessment. The general verdict from the check list type evaluations in nine relevant systematic reviews was that Burke et al. (1991) is a good quality trial. All relevant meta-analyses extensively used its data to formulate therapeutic evidence. My comprehensive evaluation, on the other hand, brought to the surface a series of serious problems in the design, conduct, analysis and report of this trial that were missed by the earlier evaluations. A check-list or instrument based approach, if used as a short-cut, may at times rate deeply flawed trials as good quality trials. Check lists are crucial but they need to be augmented with an in-depth review, and where possible, a scrutiny of the protocol, trial records, and original data. The extent and severity of the problems I uncovered for this particular trial warrant an independent audit before it is included in a systematic review

Pushing the limits of amplification of chirality in benzene-1,3,5-tricarboxamides

N,N’,N’’-trialkylated-benzene-1,3,5-tricarboxamides (BTAs) self-assemble via strong, threefold a–helix type intermolecular hydrogen bonding into well-defined, helical, one dimensional columnar aggregates. The introduction of a stereogenic centre into the alkyl side chains of BTAs gives rise to strong Cotton effects in dilute apolar solutions indicating the preference for one helical conformation over the other. Here, we summarise our research on the influence of the position of the stereogenic centre on the aggregate stability and the degree of amplification of chirality in BTAs. In addition, we disclose our results on creating a preferred helical sense in BTAbased supramolecular polymers by introducing H/D isotope chirality into the alkyl side chains of BTAs at the a-position. We determine the relative stabilities of the leftand right-handed helical conformers formed by these deuterated molecules by performing a conformational analysis in different alkane solvents. Our findings show that the subtle difference between the stabilities of the two conformers leads to a cooperative self-assembly process, which is highly sensitive to the applied solvent

Designing processive catalytic systems. Threading polymers through a flexible macrocycle ring

Contains fulltext : 131408.pdf (preprint version ) (Open Access

Pushing the limits of amplification of chirality in benzene-1,3,5-tricarboxamides

N,N’,N’’-trialkylated-benzene-1,3,5-tricarboxamides (BTAs) self-assemble via strong, threefold a–helix type intermolecular hydrogen bonding into well-defined, helical, one dimensional columnar aggregates. The introduction of a stereogenic centre into the alkyl side chains of BTAs gives rise to strong Cotton effects in dilute apolar solutions indicating the preference for one helical conformation over the other. Here, we summarise our research on the influence of the position of the stereogenic centre on the aggregate stability and the degree of amplification of chirality in BTAs. In addition, we disclose our results on creating a preferred helical sense in BTAbased supramolecular polymers by introducing H/D isotope chirality into the alkyl side chains of BTAs at the a-position. We determine the relative stabilities of the leftand right-handed helical conformers formed by these deuterated molecules by performing a conformational analysis in different alkane solvents. Our findings show that the subtle difference between the stabilities of the two conformers leads to a cooperative self-assembly process, which is highly sensitive to the applied solvent

Satisfaction of patients staying in day surgery clinic from nursing services

Objectives: To examine day surgery patients' satisfaction levels with nursing services using Scale of Patient Perception of Hospital Experience with Nursing (PPHEN). Methodology: The study design was descriptive. Data were collected by the researcher in the Day Surgery clinic of a university hospital in Turkey. Participants with literacy were 18 years old and older. The sample included 148 patients agreeing to participate in the study. Data were collected using a questionnaire including socio-demographic questions for patients and PPHEN Scale, Turkish Version adapted to Turkish by Coban. The data were assessed through descriptive statistics, t-test, Man-Whitney U Test and Kruskal Wallis variance analysis. Results: When PPHEN point averages according to age were compared, the point average for the age group of 66 years and above was 72.78 (SD= 8.28), for the age group of 19 to 40, 68.26 (SD= 11.6); and the difference between these points was found statistically significant (P= 0.041). For PPHEN point averages according to patients' educational backgrounds, it was 70.50 (SD= 10.19) for primary school graduates, 64.57 (SD=15.97) for university graduates; and the difference was found statistically significant (P= 0.000). Conclusions: In this study, it was, in general, found out that the patients were satisfied with the nursing services

Bir grup Türk popülasyonunda üçüncü molar eksikliği ile ilişkili dental anomalilerin radyografik olarak değerlendirilmesi

Bu çalışmanın amacı, bir grup Türk popülasyonunda farklı üçüncü molar agenezisi paternleri varlığındaki dental anomalileri, üçüncü molar agenezisi olmayan hastalarla karşılaştırmaktır. En az 1 adet üçüncü molar agenezisi olan 1552 hasta, üçüncü molar agenezisi paternine göre 4 gruba ayrılmış ve üçüncü molar agenezisi olmayan 402 hasta ise kontrol grubu olarak Erciyes Üniversitesi Ağız, Diş ve Çene Radyolojisi arşivinden rastgele seçilmiştir. Panoramik radyograflar hipodonti, hiperdonti, gömülü kalma, dilaserasyon, mikrodonti, ektopik erüpsiyon, transpozisyon ve transmigrasyon gibi dental anomalileri belirlemek için kullanılmıştır. Pearson ki-kare ve Fisher exact testleri, gruplar arasındaki dental anomalilerin dağılımındaki farklılıkları belirlemek için kullanılmıştır. Farklı üçüncü molar agenezisi paternlerine göre grupları karşılaştırdığımızda, 3 ve 4 adet üçüncü molar agenezisi olan hastalarda, diğer daimi dişlerde de daha fazla oranda agenezis tespit ettik. Ayrıca, 4 tane üçüncü molar agenezisi olan hastalar daha yüksek oranda maksiller lateral keser dişlerde mikrodontik yapı gösteriyorlardı. Diğer önemli bir bulgu da, kontrol grubu ile karşılaştırıldığında 3 ve 4 adet üçüncü molar agenezisi bulunan hastalarda toplam dental anomali prevalansının yüksek olmasıdır. Daimi diş eksikliği, maksiller lateral keserlerin mikrodontik yapıları ve total dental anomaliler tüm üçüncü molarların agenezisinin üçüncü molarların tam olduğu durumlardan daha sık oranda gözlenmektedir

The effect of isotopic substitution on the chirality of a self-assembled helix

N,N',N¿-trialkylbenzene-1,3,5-tricarboxamides (BTAs) self-assemble by means of strong, threefold a-helix-type intermolecular hydrogen bonding into well-defined, helical, one-dimensional columnar aggregates. When a stereogenic centre is introduced into the alkyl side chains of these BTAs, strong Cotton effects are observed in dilute apolar solutions, indicating the preference for one helical conformation over the other. Here, we report the creation of a helical sense preference in self-assembled BTAs by introducing deuterium/hydrogen isotope chirality into the alkyl side chains. We determine the relative stabilities of the left- and right-handed helical conformations of these deuterated supramolecular polymers by performing a conformational analysis. Our findings show that the results of deuterium/hydrogen substitution in BTA-based supramolecular polymers and helical polyisocyanates are very similar, although the formation mechanisms differ. The selectively deuterated BTAs discussed here represent the first example of supramolecular chirality resulting from isotope substitution