Preparation, characterization and application of ion exchangers with cyclic polyether anchor groups

Hybrid and biohybrid silicate based materials: molecular vs. block-assembling bottom–up processes

“…In this way, macrocycles grafted to silica can be applied in chromatography either for separation of cations (e.g., alkaline and alkaline earth, heavy and noble metals), separation of anions (e.g., halides, pseudohalides, isopolyacids, heteropolyacids), or separation of non-charged compounds. 77,78,[82][83][84] For instance, benzo-crowns linked in different ways on silica exhibit variable separation ability towards alkaline ions. Thus, benzo-18C6/silica columns show excellent discrimination of cations with retention time increasing in the sequence:…”

Monobactams. Preparation of (S)-3-amino-2-oxoazetidine-1-sulfonic acids from L-.alpha.-amino-.beta.-hydroxy acids via their hydroxamic esters

“…These values are similar to those previously determined for general-acid catalysis of the same reaction of 4-and 3-formyl-1methylpyridinium ions. 2 General-acid catalysis for 2-pyridinecarboxaldehyde phenylhydrazone formation could not be detected in cyanoacetate, chloroacetate, formate, /3-bromopropionate, and acetate buffers (pH range 1.9-4.7) up to a concentration of the acidic form of the buffer of 0.1 M. This means that neither amine addition or carbinolamine dehydration is subject to detectable general-acid catalysis. In this respect also, phenylhydrazone formation from 2pyridinecarboxaldehyde is distinct from that with 2formyl-l-methylpyridinium ion, for which general-acid catalysis of carbinolamine dehydration (a = 0.7) is observed.…”

“…In this respect also, phenylhydrazone formation from 2pyridinecarboxaldehyde is distinct from that with 2formyl-l-methylpyridinium ion, for which general-acid catalysis of carbinolamine dehydration (a = 0.7) is observed. 2 The general-acid catalysis of most addition reactions of nitrogen nucleophiles to the carbonyl group involves trapping of the zwitterionic intermediate, T*, by diffusion-controlled proton transfer. 10,11,13 For the in-termediate T* from this aldehyde, the necessary proton transfer could probably occur intramolecularly, as shown below, or through a water molecule, with a rate that is even faster than diffusion together of T* and an external catalyst, thus avoiding the need for general-acid catalysis, as observed.…”

Ion-Binding Properties of Crown Ether and Cryptand Containing Polymers

“…Blasius and his co-workers synthesized several types of polymer networks containing crown ether or cryptand structures (2)(3)(4). The structures of some of the materials are shown in Figure 1.…”