Synthesis and spectroscopic characterisation of fluorescent indicators for Na+ and K+ based on (di)pyridino crown ethers

Abstract

thienyl}isophthalate (BIPY) are reported. To investigate the effect of an sp 2 -nitrogen in the aza-crown ether cavity on the complex formation behaviour, a (bi)pyridino crown compound with an appropriate cavity for the sodium and the potassium cation, respectively, is linked to an aryl thiophene fluorophore. New, versatile routes for the synthesis of 4-substituted pyridino crown ethers and 4,4Ј-substituted sym-dipyridino crown ethers are described. The chelating abilities of the indicators with monovalent cations have been studied in aqueous solution by their fluorescence properties. Both the free and complexed forms of the indicators have an absorption maximum around 345 nm and an emission maximum at 410 nm, displaying only a decrease in the fluorescence intensity upon cation binding. While SPYR cannot discriminate between Na ϩ and other monovalent cations, PPYR and BIPY show a peak selectivity for K ϩ with a dissociation constant of 1.2 ± 0.3 mM and 4.4 ± 0.7 mM, respectively.

Application of Flow Chemistry to Macrocyclization of Crown Ethers

“…Macrocyclization reactions resulting pyridino-18-crown-6 ethers in batch mode Scheme 2. Preparation of diiodide derivatives is in accordance with our earlier results from our group [16,17,[21][22][23]25] and also those of others [20,24]. We presume that the solubility of the appropriate alkali iodide in tetrahydrofuran plays an important role in this type of macrocyclization reaction.…”

“…Preparation of crown ethers 2-12 (Scheme 1) in batch mode is already published [16,17,[20][21][22][23][24][25]. Here, we describe a new continuous-flow method applying a column which contained a solid base for their synthesis, which provides better yields in shorter reaction times.…”

“…This macrocyclization is a Williamsontype ether formation reaction, where alkylation of primary or secondary alcohols is carried out with alkyl tosylates after a deprotonation step applying NaH [16,17,[20][21][22][23][24][25]. Using batch conditions this reaction takes place up to 120 hours and usually provides poor yields.…”

Buffering Heavy Metal Ions with Photoactive CrownCast Cages

“…In addition to heteroatom substitution, expansion of the A15C5 ring by one ethylene glycol unit provides the corresponding 16‐phenyl‐1,4,7,10,13‐pentaoxa‐16‐azacyclooctadecane (A18C6, 6 ) ligand. In the parent crown ethers, 15‐crown‐5 has a slight preference for Na + over K + , whereas 18‐crown‐6 has the opposite selectivity 39,40. In the corresponding N ‐aryl‐azamacrocycles, A18C6 has some preference for Pb 2+ ,20 a large divalent metal ion, based on the size of the binding cavity.…”

Catalytic Asymmetric Aldol Reactions in Aqueous Media Using Chiral Bis‐pyridino‐18‐crown‐6—Rare Earth Metal Triflate Complexes.

“…The combined organic phases were dried over MgSO 4 , and concentrated in vacuo. The residue was purified by chromatography (silica gel, hexane/ethyl acetate (1/6)) to afford 14 (19% yield) as a colorless oil: 1 H NMR (CDCl 3 ) δ 1.00 (t, 6H, J = 7.3 Hz), 1.02 (t, 6H, J = 7.3 Hz), 1.37-1.80 (m, 8H), 3.28 (dt, 2H, J = 6.7, 4.6 Hz), 3.58 (dt, 2H, J = 7.3, 3.5 Hz), 4.68 (d, 2H, J = 13.0 Hz), 4.87 (d, 2H, J = 13.2 Hz), 5.32 (brs), 7.18 (d, 2H, J = 7.7 Hz), 7.66 (t, 1H, J = 7.7 Hz); 13 26 D +7.4 (c 1.00, EtOH).…”