dehydration of primary amides to nitriles efficiently proceeds undermild, aqueous conditions via the use of dichloroacetonitrile as a water acceptor. A key to the design of this transfer dehydration catalysis is the identification of an efficientwater acceptor, dichloroacetonitrile, that preferentially reacts with amides over other polar functional groups with the aid of the Pd catalyst and makes the desired
Electrically Fueled Active Supramolecular Materials
作者:Serxho Selmani、Eric Schwartz、Justin T. Mulvey、Hong Wei、Adam Grosvirt-Dramen、Wyeth Gibson、Allon I. Hochbaum、Joseph P. Patterson、Regina Ragan、Zhibin Guan
DOI:10.1021/jacs.2c01884
日期:2022.5.4
electrochemical redox reaction network, a transient and highly active supramolecularassembly is achieved with rapid kinetics, directionality, and precise spatiotemporal control. As electronic signals are the default information carriers in modern technology, the described approach offers a potential opportunity to integrate active materials into electronic devices for bioelectronic applications.
作者:Tellis A. Martin、David H. Causey、A. Leonard. Sheffner、Allan G. Wheeler、John R. Corrigan
DOI:10.1021/jm00318a046
日期:1967.11
Anatomy of a Gel. Amino Acid Derivatives That Rigidify Water at Submillimolar Concentrations
作者:Fredric M. Menger、Kevin L. Caran
DOI:10.1021/ja0016811
日期:2000.11.1
On the basis of suggestive X-ray data, 14 aroyl L-cystine derivatives were designed, synthesized, and examined for their ability to gelate water. Several members of this amino acid family are remarkably effective aqueous gelators (the best being one that can rigidify aqueous solutions at 0.25 mM, ca. 0.01%, in less than 30 s!). A few of the analogues separate from water as crystals, indicating a close relationship between gelation and crystallization. All effective gelators self-assemble into fibrous structures that entrain the solvent in the capillary spaces among them. Hydrogen-bonding sites on the compounds that might stabilize the fibers were identified from specific substitutions that replace a hydrogen donor with a methyl group, enhance the hydrogen-accepting ability of a carbonyl oxygen, or promote the hydrogen-donating, ability of an amide proton. The structural variations were characterized via minimal gelation concentrations and times, X-ray crystallography, light and electron microscopy, rheology, and calorimetry. The multiple techniques, applied to the diverse compounds, allowed an extensive search into the basis of gelation. It was learned, for example, that the compound with the lowest minimum gelator concentration and time also has one of the weakest gels (i.e., it has a low elastic modulus). This is attributed to kinetic effects that perturb the length of the fibers. It was also argued that pi/pi stacking, the carboxyl carbonyl (but not the carboxyl proton), and solubility factors all contribute to the stability of a fiber. Polymorphism also plays a role. Rheological studies at different temperatures show that certain gels are stable to a 1-Hz, 3-Pa oscillating shear stress at temperatures as high as 90 degreesC. Other gels have a "catastrophic" break at lower temperatures. Calorimetric data indicate a smooth transition from gel to sol as the temperature is increased. These and other issues are discussed in this "anatomy" of a gel.