Self-assembly and semiconductivity of an oligothiophene supergelator

• Pampa Pratihar,
• Suhrit Ghosh,
• Vladimir Stepanenko,
• Sameer Patwardhan,
• Ferdinand C. Grozema,
• Laurens D. A. Siebbeles and
• Frank Würthner

Beilstein J. Org. Chem. 2010, 6, 1070–1078, doi:10.3762/bjoc.6.122

• ability of T1 to gelate such a wide range of solvents and its significantly low CGC values can be attributed to the favourable balance between the self-assembly propensity of the gelator and good solubility due to the presence of the trialkoxybenzamide groups. AFM investigations The topology of gels of

Expanding the gelation properties of valine-based 3,5-diaminobenzoate organogelators with N-alkylurea functionalities

• Hak-Fun Chow and
• Chin-Ho Cheng

Beilstein J. Org. Chem. 2010, 6, 1015–1021, doi:10.3762/bjoc.6.114

• poor organogelators, while the longer aliphatic chain analogues (n ≥ 10) formed transparent gels in aromatic solvents and translucent gels in 1,4-dioxane, DMF and DMSO. Most interestingly, it was observed that organogelator 2 (n = 20) with the longest hydrocarbon chain also formed opaque gels in

• alcoholic solvents and translucent gels in alicyclic hydrocarbon solvents, respectively. Hence, the range of the solvents that these new compounds can gel was significantly expanded by replacing the Cbz group with an N-alkylurea functionality. Based on these experiments, organogelators 2 with longer

• crystallization of the self assembled aggregates during gelation, producing gels with a higher Tg and a lower MGC value. Experimental General. Optical rotation measurements were conducted in DMSO (unless otherwise stated) and below the MGC to avoid molecular aggregation or gelation and were measured with a Perkin

Insights into the mechanical properties of a silicone oil gel with a ‘latent’ gelator, 1-octadecylamine, and CO₂ as an ‘activator’

• Emiliano Carretti,
• Mathew George and
• Richard G. Weiss

Beilstein J. Org. Chem. 2010, 6, 984–991, doi:10.3762/bjoc.6.111

• , DE 19711, USA 10.3762/bjoc.6.111 Abstract A detailed study of the rheological properties of silicone oil gels, made from a low-molecular-mass organic gelator, a combination of 1-octadecylamine (a latent gelator) and carbon dioxide (an ‘activating’ molecule), is reported. Information gleaned from the

• the basis for anisotropic self-assembly and recognition of the potential applications for such gels [4][5][6] – most can be reverted thermally to their solution (or sol) states – as models for several important biological aggregates (e.g., that are involved with neurodegenerative and other diseases

• triatomic gas [8][9], especially carbon dioxide [10][11], is added). Although the structures of SAFINs and rheological properties of their gels made with ‘normal’ LMOGs have been extensively investigated [2][12], the mechanical properties of gels made from latent LMOGs have not received much attention

Differences between β-Ala and Gly-Gly in the design of amino acids-based hydrogels

• Andreea Pasc,
• Firmin Obounou Akong,
• Sedat Cosgun and
• Christine Gérardin

Beilstein J. Org. Chem. 2010, 6, 973–977, doi:10.3762/bjoc.6.109

• molecular weight polymers, physically or chemically cross-linked, but in the recent past, their construction by low molecular weight (LMW) compounds has been explored. With respect to polymeric hydrogels, supramolecular gels of LMWGs (low molecular weight gelators) are assembled by non-covalent forces, such

• building blocks for supramolecular architectures such as gels [8][9]. The structure of the surfactant is a major factor for their gelator properties. As reported in the literature [1], unless the molecules remain in solution, when a hot, homogeneous solution of the gelator, is cooled, the molecules start

• -Ala or Gly-Gly, respectively, formed hydrogels [10][11]. Gly-Gly-His-EO2-C14 formed lamellar phases, the gels were transparent and the gel-to-sol transition temperatures were lower with respect to the β-Ala-derivative. In order to understand better the differences between the two compounds, NMR, X-ray

Towards racemizable chiral organogelators

• Jian Bin Lin,
• Debarshi Dasgupta,
• Seda Cantekin and
• Albertus P. H. J. Schenning

Beilstein J. Org. Chem. 2010, 6, 960–965, doi:10.3762/bjoc.6.107

• building blocks with co-added organizational information can make these gels responsive. In recent years, much effort has been devoted to the design and characterization of chiral self-assembled fibrillar networks that form organogels [1][2]. In such systems the chirality within a molecular building block

• macroscopic behavior. Most of the earliest stimuli-responsive gels undergo a UV-induced transformation, which can be reversed by visible light. For example, Shinkai and coworkers demonstrated that trans-cis isomerization of gelator compounds by UV/visible light could induce a gel-sol transition [6]. Feringa

• and coworkers have reported a chiral gelator in which the supramolecular organization of the chiral assemblies can be switched using UV/visible light combined with heating and cooling [7]. Chiral gels that respond to other stimuli such as metal ions [8], guest molecules [9] and temperature [10] have

Oxalyl retro-peptide gelators. Synthesis, gelation properties and stereochemical effects

• Janja Makarević,
• Milan Jokić,
• Leo Frkanec,
• Vesna Čaplar,
• Nataša Šijaković Vujičić and
• Mladen Žinić

Beilstein J. Org. Chem. 2010, 6, 945–959, doi:10.3762/bjoc.6.106

• -assembly motifs, chirality effects and morphological characteristics of gels formed by chiral retro-dipeptidic gelators in the form of terminal diacids (1a–5a) and their dimethyl ester (1b–5b) and dicarboxamide (1c–5c) derivatives. Terminal free acid retro-dipeptides (S,S)-bis(LeuLeu) 1a, (S,S)-bis(PhgPhg

• cases such organization results in formation of gels consisting of self-assembled fibrous aggregates usually containing a large volume of solvent [16]. In gels, the fibers are heavily entangled into 3-dimensional networks which immobilize the solvent and prevent fluidity in the system [17][18][19][20

• [42][43]. Hence, systematic studies of gels formed by structurally diverse small gelator molecules comprising elucidation of their self-assembly motifs, gelation effectiveness toward solvents of different structure and physical characteristics, estimation of solvation and stereochemical effects and

Chain stopper engineering for hydrogen bonded supramolecular polymers

• Thomas Pinault,
• Bruno Andrioletti and
• Laurent Bouteiller

Beilstein J. Org. Chem. 2010, 6, 869–875, doi:10.3762/bjoc.6.102

• Cedex, France 10.3762/bjoc.6.102 Abstract Supramolecular polymers are linear chains of low molar mass monomers held together by reversible and directional non-covalent interactions, which can form gels or highly viscous solutions if the self-assembled chains are sufficiently long and rigid. The

• held together by reversible and highly directional non-covalent interactions [1][2][3]. Because of their macromolecular architecture, they can display polymer-like rheological properties, and they can, in particular, form gels if the self-assembled chains are sufficiently long and rigid [4][5][6][7][8

• need to be heated and then cooled to form a gel. Moreover, the gels formed are usually visco-elastic, meaning that they show an elastic response only at high frequencies. The chain length of a supramolecular polymer depends on the strength of the association between the monomers, which is highly

Pyridinium based amphiphilic hydrogelators as potential antibacterial agents

• Sayanti Brahmachari,
• Sisir Debnath,
• Sounak Dutta and
• Prasanta Kumar Das

Beilstein J. Org. Chem. 2010, 6, 859–868, doi:10.3762/bjoc.6.101

• ; hydrogel; pyridinium; self-assembly; Introduction Gels are an outstanding group of soft materials lying at the interface of solid and liquid, and find numerous applications in various fields including tissue engineering, biosensors, food processing, cosmetics, photography, controlled drug delivery etc. [1

• ][2][3][4][5][6][7][8][9][10][11]. Amongst the variety of gels, hydrogels (those that entrap water) are of special importance owing to their tremendous potential in biomedicine [12][13][14][15][16]. These hydrogels can be of natural origin [17] (collagens, polysaccharides) as well as of synthetic

• gelation. The planar aromatic moiety favors π–π stacking interactions between the molecules and leads to the formation of 3D networks of viscoelastic gels [25][26][27]. Interestingly, among all these aromatic rings, the positively charged pyridine (pyridinium) unit is well known to impart antibacterial

Chiral gels derived from secondary ammonium salts of (1R,3S)-(+)-camphoric acid

• Tapas Kumar Adalder,
• N. N. Adarsh,
• Ravish Sankolli and
• Parthasarathi Dastidar

Beilstein J. Org. Chem. 2010, 6, 848–858, doi:10.3762/bjoc.6.100

• Tapas Kumar Adalder N. N. Adarsh Ravish Sankolli Parthasarathi Dastidar Indian Association for the Cultivation of Science, Kolkata, India Indian Institute of Science, Bangalore, India 10.3762/bjoc.6.100 Abstract In order to have access to chiral gels, a series of salts derived from (1R,3S

• )-(+)-camphoric acid and various secondary amines were prepared based on supramolecular synthon rationale. Out of seven salts prepared, two showed moderate gelation abilities. The gels were characterized by differential scanning calorimetry, table top rheology, scanning electron microscopy, single crystal and

• ; supramolecular gels; supramolecular synthon; Introduction A gel is a two component system which is mainly liquid with a very little amount of solid. In gel state, gelator molecules form 3-D networks within which solvent molecules are trapped thus resulting in a gel. Depending on the nature of the network, gels

Organic gelators and hydrogelators

• Jean-Pierre Desvergne

Beilstein J. Org. Chem. 2010, 6, 846–847, doi:10.3762/bjoc.6.99

• supramolecular network (in the case of supergelators it is not rare to observe more than 104 molecules of solvent per molecule of gelator in the gel composition), thus creating extraordinary variations of the physical properties of the system. These physical gels are usually thermoreversible (reversible sol-gel

• different approaches for producing molecular gelators, and some techniques used for the characterization and the properties of the gels. It is my great pleasure to act as guest editor of this Thematic Series, which gathers a wide range of expertise to meet the demands of this interdisciplinary field. I

Polyionic polymers – heterogeneous media for metal nanoparticles as catalyst in Suzuki–Miyaura and Heck–Mizoroki reactions under flow conditions

• Klaas Mennecke and
• Andreas Kirschning

Beilstein J. Org. Chem. 2009, 5, No. 21, doi:10.3762/bjoc.5.21

• likely to be made responsible for the stabilization of the nanoparticles which results in low degree of leaching [25][26][27][28][29]. It has to be noted that like many other heterogenized Pd sources [15][16][36][37][38][39][40][41] these polyionic gels very likely also serve as reservoirs for Pd

• sources for soluble, catalytically active species during the course of Heck and Suzuki couplings. They note a solution-phase contribution for catalysis and determined leaching up to 46% in DMF as solvent which is significantly higher compared to our polyionic gels: Broadwater, S. J.; McQuade, D. T. J

A simple route for renewable nano- sized arjunolic and asiatic acids and self- assembly of arjuna- bromolactone

• Braja G. Bag,
• Partha P. Dey,
• Shaishab K. Dinda,
• William S. Sheldrick and
• Iris M. Oppel

Beilstein J. Org. Chem. 2008, 4, No. 24, doi:10.3762/bjoc.4.24

• and asiatic acid was established from the HPLC peak areas of the corresponding methyl esters. While attempting crystallization of arjuna-bromolactone 3 from various solvents we serendipitously discovered that it formed gels efficiently in various aromatic solvents (Table 1) [17][18]. In benzene as the

• solvent, compound 3 formed a transparent gel that was stable for several weeks. But the transparent gel in mesitylene gave rise to the formation of crystals, with concomitant cleavage of the gel network, on standing at room temperature for about a day. Scanning electron micrographs of the dried gels

• with angles at the H atoms of 157.2(3)°, 167.1(3)° and 152.1(3)° respectively. Conclusion In conclusion, we have developed a simple route to obtain the nano-sized arjunolic and asiatic acids in pure form affording >75% overall isolated yield of the materials. The nano-sized bromolactone 3 formed gels

N-1 regioselective Michael- type addition of 5-substituted uracils to (2-hydroxyethyl) acrylate

• Sławomir Boncel,
• Dominika Osyda and
• Krzysztof Z. Walczak

Beilstein J. Org. Chem. 2007, 3, No. 40, doi:10.1186/1860-5397-3-40

• hydrophilic polymer gels,[11] has not been considered frequently as a potential Michael acceptor in organic synthesis.[12][13] We have developed an effortless, efficient and useful pathway for the synthesis of 2-hydroxyethyl-3-(uracil-1-yl)propanoates. The products of addition may be further functionalized