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Aliphatic Spacer (aliphatic + spacer)
Selected AbstractsSynthesis, characterization, and cure reaction of methacrylate-based multifunctional monomers for dental compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Mousa Ghaemy Abstract The synthesis of 2,2-bis[(4-(2-hydroxy-3-methacryloxyethoxy)phenyl]propane (BHEP) and (1-methacryloxy-3-ethoxymethacryloxy-2-hydroxy)propane (MEHP) for use as the monomer phase in dental composites are reported. The monomers were prepared by the reaction of 2-hydroxyethyl methacrylate (HEMA) with diglycidyl-ether of bisphenol A (DGEBA) and with glycidyl methacrylate (GMA), respectively. The progress of the reaction was followed by measuring the disappearance of the epoxide group peak using FTIR and the structure of the monomers was characterized by 1H-NMR. BHEP and MEHP have lower viscosity because of the presence of long aliphatic spacer on both sides of the aromatic ring in BHEP and the absence of aromatic rings and the presence of only one hydroxyl group in each molecule of MEHP. Thermal curing of the monomers was conducted in a DSC using benzoyl peroxide as an initiator. Photopolymerization of the monomers was also conducted with the visible light using camphorquinone and N,N -dimethylaminoethyl methacrylate as the photoinitiating system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Bivalent phenethylamines as novel dopamine transporter inhibitors: evidence for multiple substrate-binding sites in a single transporterJOURNAL OF NEUROCHEMISTRY, Issue 6 2010Kyle C. Schmitt J. Neurochem. (2010) 112, 1605,1618. Abstract Bivalent ligands , compounds incorporating two receptor-interacting moieties linked by a flexible chain , often exhibit profoundly enhanced binding affinity compared with their monovalent components, implying concurrent binding to multiple sites on the target protein. It is generally assumed that neurotransmitter sodium symporter (NSS) proteins, such as the dopamine transporter (DAT), contain a single domain responsible for recognition of substrate molecules. In this report, we show that molecules possessing two substrate-like phenylalkylamine moieties linked by a progressively longer aliphatic spacer act as progressively more potent DAT inhibitors (rather than substrates). One compound bearing two dopamine (DA)-like pharmacophoric ,heads' separated by an 8-carbon linker achieved an 82-fold gain in inhibition of [3H] 2,-carbomethoxy-3,-(4-fluorophenyl)-tropane (CFT) binding compared with DA itself; bivalent compounds with a 6-carbon linker and heterologous combinations of DA-, amphetamine- and ,-phenethylamine-like heads all resulted in considerable and comparable gains in DAT affinity. A series of short-chain bivalent-like compounds with a single N -linkage was also identified, the most potent of which displayed a 74-fold gain in binding affinity. Computational modelling of the DAT protein and docking of the two most potent bivalent (-like) ligands suggested simultaneous occupancy of two discrete substrate-binding domains. Assays with the DAT mutants W84L and D313N , previously employed by our laboratory to probe conformation-specific binding of different structural classes of DAT inhibitors , indicated a bias of the bivalent ligands for inward-facing transporters. Our results strongly indicate the existence of multiple DAT substrate-interaction sites, implying that it is possible to design novel types of DAT inhibitors based upon the ,multivalent ligand' strategy. [source] Lightly crosslinked, mesomorphic networks obtained through the reaction of dimeric, liquid-crystalline epoxy,imine monomers and heptanedioic acidJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2006David Ribera Abstract We reacted various dimeric, liquid-crystalline epoxy,imine monomers, differing in the length of the central aliphatic spacer or the dipolar moments, with heptanedioic acid. The resulting systems showed a liquid-crystalline phase in some cases, depending on the dimer and on the reaction conditions. The systems were characterized with respect to their mesomorphic properties and then were submitted to dynamic mechanical thermal analysis in both fixed-frequency and frequency-sweep modes in the shear sandwich configuration. The arrangement in the liquid-crystalline phase seemed to be mainly affected both by the polarization of the mesogen and by the reaction temperature, which favored the liquid-crystalline arrangement when it was lying in the range of stability of the dimer mesophase. In agreement with other recent literature data, dynamic mechanical thermal analysis results suggested that the presence of the mesogen directly incorporated into the main chain increased the lifetimes of the elastic modes both in the isotropic phase and in the liquid-crystalline phase with respect to side-chain liquid-crystalline elastomers and that the time,temperature superposition principle did not hold through the liquid-crystalline-to-isotropic transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6270,6286, 2006 [source] Synthesis and optical properties of soluble polyethers containing oligophenyl in the main chain and p -styrylbenzene side groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2002Ioakim K. Spiliopoulos Abstract New polyethers containing alternating conjugated segments of p -terphenyl or p -quinquephenyl with p -styrylbenzene side groups and aliphatic spacers were synthesized with pyrylium salts. They had moderate molecular weights, were amorphous, and dissolved in tetrahydrofuran, chloroform, and other common organic solvents. The glass-transition temperatures were 68,82 and 110,153 °C for the polymers that carried p -terphenyl and p -quinquephenyl moieties, respectively. The absorption spectra showed a peak around 325 nm, and the band gaps were 3.27,3.34 eV, which were calculated from the onset absorption in solution. The photoluminescence maxima were at 393,398 nm in solution and 422,449 nm in thin films, indicating that the polymers were violet-blue-emitting materials. The photoluminescence quantum yields in solution were up to 0.25. The polymers displayed both in concentrated solutions and in the solid state intramolecular or intermolecular interactions. The polarity of the solvent influenced the shape of the photoluminescence curve. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 682,693, 2002; DOI 10.1002/pola.10151 [source] pH-Triggered Dethreading,Rethreading and Switching of Cucurbit[6]uril on Bistable [3]Pseudorotaxanes and [3]RotaxanesCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2008Dönüs Tuncel Dr. Abstract A series of water-soluble [3]rotaxanes-(n+2) and [3]pseudorotaxanes-(n+2) with short (propyl, n=1) and long (dodecyl, n=10) aliphatic spacers have been prepared in high yields by a 1,3-dipolar cycloaddition reaction catalyzed by cucurbit[6]uril (CB6). The pH-triggered dethreading and rethreading of CB6 on these pseudorotaxanes was monitored by 1H,NMR spectroscopy. A previously reported [3]rotaxane-12 that is known to behave as a bistable molecular switch has two recognition sites for CB6, that is, the diaminotriazole moieties and the dodecyl spacer. By changing the pH of the system, it is possible to observe more than one state in the shuttling process. At low pH values both CB6 units are located on the diaminotriazole moieties owing to an ion,dipole interaction, whereas at high pH values both of the CB6 units are located on the hydrophobic dodecyl spacer. Surprisingly, the CB6 units shuttle back to their initial state very slowly after reprotonation of the axle. Even after eighteen days at room temperature, only about 50,% of the CB6 units had relocated back onto the diaminotriazole moieties. The rate constants for the shuttling processes were measured as a function of temperature over the range from 313 to 333,K and the activation parameters (enthalpy, entropy, and free energy) were calculated by using the Eyring equation. The results indicate that this [3]rotaxane behaves as a kinetically controlled molecular switch. The switching properties of [3]rotaxane-3 have also been studied. However, even under extreme pH conditions this rotaxane has not shown any switching action, which confirms that the propyl spacer is too short to accommodate CB6 units. [source] Anion Recognition by Neutral Macrocyclic AmidesCHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005J. Chmielewski Dr., Micha Abstract Although amides often serve as anchoring groups in natural and synthetic anion receptors, the structure,affinity relationship studies of amide-based macrocyclic receptors are still very limited. Therefore, we decided to investigate the influence of the size of the macroring on the strength and selectivity of anion binding by uncharged, amide-based receptors. With this aim, we synthesized a series of macrocyclic tetraamides derived from 2,6-pyridinedicarboxylic acid and aliphatic ,,,-diamines of different lengths. X-ray analysis shows that all ligands studied adopt expanded conformations in the solid state with the convergent arrangement of all four hydrogen-bond donors. 1H NMR titrations in DMSO solution revealed a significant effect of the ring size on the stability constants of anion complexes; the 20-membered macrocyclic tetraamide 2 is a better anion receptor than its both 18- and 24-membered analogues. This effect cannot be interpreted exclusively in terms of matching between anion diameter and the size of macrocyclic cavity, because 2 forms the most stable complexes with all anions studied, irrespective of their sizes. However, geometric complementarity manifests in extraordinarily high affinity of 2 towards the chloride anion. The results obtained for solutions were interpreted in the light of solid-state structural studies. Taken together, these data suggest that anion binding by this family of macrocycles is governed by competitive interplay between their ability to adjust to a guest, requiring longer aliphatic spacers, and preorganization, calling for shorter spacers. The 20-membered receptor 2 is a good compromise between these factors and, therefore, it was selected as a promising leading structure for further development of anion receptors. Furthermore, the study of an open chain analogue of 2 revealed a substantial macrocyclic effect. X-ray structure of the acyclic model 14 suggests that this may be due to its ill-preorganized conformation, stabilized by two intramolecular hydrogen bonds. [source] | ||||||||||