Bis(carbazolyl)ureas as Selective Receptors for the Recognition of Hydrogenpyrophosphate in Aqueous Media

Abstract

Recognition properties of the novel bis(carbazole) tris-ureidic-based receptors 1 and 2 toward different anions have been studied by (1)H NMR and absorption and emission spectroscopy, as well as by DFT calculations. Receptor 1, in which the two urea-functionalized arms are decorated with p-nitrophenyl rings, behaves as a highly selective chromogenic molecular probe for hydrogenpyrophosphate anion in a competitive medium (acetonitrile/water, 70/30). Receptor 2, bearing two urea arms decorated with photoactive pyrenyl rings, acts as a highly selective fluorescent molecular probe for hydrogenpyrophosphate anion in either acetonitrile or an aqueous mixture (acetonitrile/water, 85/15). Receptor 2 exhibits a dual monomer-excimer emission spectrum and undergoes a remarked ratiometry in acetonitrile in the presence of hydrogenpyrophosphate: the excimer band disappears, whereas the monomer band is slightly increased. However, in the aqueous mixture, a strong increase of the excimer emission band was observed, while the monomer emission bands remained almost unaffected. The resulting binding modes and spectroscopic features are explained by suitable structures of model complexes for both receptors. In such complexes, a peripheral cooperative effect was found, alleviating the excess of negative charge in the guest toward the outer surface of the host, as well as the required enlargement on its internal cavity.

Anion binding with urea and thiourea derivatives

“…Espinoza, Molina et al synthesized trisurea receptor 114a bearing carbazoles and urea binding sites as compared with indole receptor 35a with amide groups (Figs. 24 and 80)[132]. Additional urea moieties in 114a enabled stronger binding with two additional H-bonds compared with 35a.…”

Comparing Isomeric Tridentate Carbazole‐Based Click Ligands: Metal Complexes and Redox Chemistry

“…From the fact that those of Ru(btc1) 2 showed an EPR signal, indicating the presence of Ru(btc1) 2 + cations, which, however,c ould not be furthere lucidated, it hadt ob e concluded that there may be some ambiguity about the determined bond lengths and angles. The bite angles found in Ru(btc2) 2 are significantly larger (177.43 (13) and 178.89 (11)8), than corresponding angles in Ru-btp complexes (156.78)a nd enablet he almost perfect octahedral arrangementoft he donors. The molecular structure of Ru(btc2) 2 is however reliable, and shown in Figure 1.…”

“…[9] Hbtc2, on the other hand, was obtained by starting from the 1,8-diamino-carbazole derivative, [13] which was converted to the corresponding 1,8-bisazide, followed by CuAACw ith the bis(tert-butyl)phenyl acetylene. On the one hand, Hbtc1 was synthesized by CuAAC of the in situ generatedb is-(tert-butyl)phenyl azide with the complementary 1,8-diethynylcarbazole.…”

“…Synthesis of Hbtc2: NaNO 2 (1.338 g, 19.389 mmol) in H 2 O( 10 mL) was added to as olution of 1,8-diamino-3,6-di-tert-butyl-9H-carbazole [13] (2.00 g, 6.463 mmol), in EtOH/H 2 O( 4:1, 50 mL) over 30 min at 0 8Ca nd subsequently stirred at this temperature for 1h.N aN 3 (1.260 g, 19.389 mmol) in H 2 O( 10 mL) was added to the reaction mixture at 0 8Cw ithin 30 min and subsequently stirred at ambient temperature for 1h.T he mixture was extracted with ethyl acetate (3 50 mL) and the combined organic phases were dried with MgSO 4 .A fter column chromatography (petroleum ether/ethyl acetate = 20:1) 1,8-diazido-3,6-di-tert-butyl-9H-carbazole (0.896 g, 38 % crude) was obtained, which was used without further purification. The crude azide (1.230 g, 3.403 mmol), 3,5-di-tert-butylphenyl acetylene [14] (2.188 g, 10.209 mmol), ascorbic acid (67 mg, 0.340 mmol), 1 m aqueous CuSO 4 (0.25 mL, 0.340 mmol), and TBTA( 180 mg, 0.340 mmol) in CH 2 Cl 2 /tertBuOH/H 2 O( 4:4:1, 35 mL) were stirred at ambient temperature overnight.…”

Fluorescent asymmetric bis-ureas for pyrophosphate recognition in pure water

“…14 Many different strategies have been developed for designing fluorescent chemosensors for Ppi including the use of charged receptors, 15,16 metal complexes, [17][18][19][20][21] or neutral receptors in particular urea or thiourea receptors. 15,[22][23][24][25][26] We have recently described a new family of symmetric bis-urea receptors which showed a remarkable affinity for Ppi and were able to act as a fluorimetric chemosensors for this anion, even at naked eye. 27 In particular we demonstrated that the presence of naphtyl groups as pendant arms of the ureas, facilitates the binding and the optical fluorimetric selectivity thanks to the uncommon interaction of an aromatic CH from the fluorophore with the Ppi guest.…”