1,061 research outputs found
Consequences of cooperativity in supramolecular polymers
Full text linkN,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
Hydrolases part I : enzyme mechanism, selectivity and control in the synthesis of well-defined polymers
No full textLipases are highly activity in the polymerization of a range of monomers. Both ring-opening polymerization of cyclic esters and polycondensation reactions of AA–BB and AB monomers have been investigated in great detail. This paper reviews the increased understanding in enzymatic strategies for the production of well-defined polymers. Major advantages of enzymatic catalysts are the relatively mild reaction conditions, and the often-observed excellent regio-, chemo-, and enantioselectivity that allow for the direct preparation of functional materials. However, as a result of the monomer activation mechanism, polymers of low polydispersity and low quantitative degree of endgroup functionality are difficult to attain. A wide variety of (co)polymers have been synthesized and explored in a variety of applications using lipase catalysts
CCDC 992565: Experimental Crystal Structure Determination
No full textAn entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures. Related Article: Wilco P. J. Appel, Marko M. L. Nieuwenhuizen, Martin Lutz, Bas F. M. de Waal, Anja R. A. Palmans, E. W. Meijer|2014|Chemical Science|5|3735|doi:10.1039/C4SC00871
CCDC 2377271: Experimental Crystal Structure Determination
No full textAn entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures. Related Article: Stefan J. D. Maessen, Siebe Lekanne Deprez, Pascal Vermeeren, Bart W. L. van den Bersselaar, Martin Lutz, Johan P. A. Heuts, Célia Fonseca Guerra, Anja R. A. Palmans|2025|Polym.Chem.|16|290|doi:10.1039/D4PY01296
Naar ladderpolymeren op basis van 2,2'-bipyridine-3,3'-diamine : nog een brug verder!
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Institutionalizing ASEAN: celebrating Europe through network governance
No full textThis article provides a new piece for two of the puzzles of institutionalized cooperation in Association of Southeast Asian Nations (ASEAN). First, with regard to the organization's four decades of existence, there has always been a marked gap between ASEAN's rhetorical goals of cooperation and its actual achievements. What explains these systematic failures of implementation? Second, from the outset, ASEAN was criticized for its light institutionalization, which failed to deliver the substantial cooperation goals. Despite selected institutional reforms, ASEAN's autonomy has not increased remarkably and it has not made any major institutional innovations. Why does ASEAN design institutions it does not use? Why does this transformation gap occur? The author suggests a sociological institutional explanation and argues that major impulses for cooperation have come from outside Southeast Asia, most importantly from Europe. By mimicking the European integration process, ASEAN member states have effectively created an isomorphic organization. The Association's institutional development reflects a concern for international legitimacy and less an objective functional demand arising from the specific interactions of member states. This copying process has led to network governance within the organization
The Vietnamese Theatrical Tradition in the Plot of Monsun, by Anja Hillin
Full text linkFrom the dramatic text Monsun by the German author Anja Hilling, this article analyzes the construction of a plot using elements of the Asian theater, in this specific case the Vietnamese tradition, identifying its presence inthe structure beyond the constant references to the context of that country, starting with the title of the play itself and the trip of one of the characters to Vietnam.A partir do texto dramático Monsun, da autora alemã Anja Hilling, este artigo analisa a construção de uma trama que se utiliza de elementos do teatro asiático, neste caso específico a tradição vietnamita, identi cando a sua presença na estrutura, além das men- ções constantes ao contexto daquele país, começando pelo próprio título da peça e pela viagem de uma das personagens ao Vietnam. 
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