Anion Sensing by a Thiourea Based Chromoionophore via Hydrogen Bonding

Abstract

Development of chromogenic receptors for biologically important substrates is one of the current research topics in analytical chemistry and biochemistry. A wide variety of chromoionophores for cations such as alkali and alkaline-earth metal ions 1 as well as amines 2,3 have been reported. In contrast, only a few chromoionophores have been reported for the colorimetric determination of anions in solution. [4][5][6][7] In design and fabrication of new anion receptors for applications in aprotic media [8][9][10][11] , the (thio)urea group as hydrogen bond donor has recently drawn much interest as a functional group for neutral receptors to recognize mono-and dicarboxylate anions, halide anions, sulfate, as well as dihydrogenphosphate etc. 6c,9-17 Wilcox et al. 17 have recently shown substituent effects in arylthiourea upon binding with a zwitterionic sulfonic acid in chloroform. In their study, some of the aryl(thio)ureas with a nitro group were found to show changes in their UV-Vis spectra upon complexation. However, these spectral changes were only utilized to assess association strengths, and no further studies of these materials as chromogenic anion receptors have been reported.We now report herein a very simple anion receptor 1 in which a p-nitrophenyl group is linked to a methylthiourea moiety. In this type of donor-acceptor chromophore, the electronic excitation is mostly accompanied by a charge transfer from donor nitrogen of the thiourea to acceptor substituent (-NO 2 ) of the chromophore.18 Thus, the excited state would be more strongly stabilized by anion binding, resulting in a bathochromic shift in the absorption maxima (l max ). Introducing the electron withdrawing substituent enhances the acidity of thiourea moiety, receptor 1 strongly binds with anions to produce an effective color change in aprotic media. Experimental Chemicals and instrumentsAll guest anions were commercially available as tetrabutylammonium salts and purified by recrystallization as described elsewhere. 16 Spectrometric grade acetonitrile was purchased from Nacalai Tesque, Inc.(Kyoto, Japan), and dried over molecular sieves 3A. 1 H NMR spectra were obtained on a JEOL a-500 spectrometer (500 MHz; JEOL DATUM, Tokyo, Japan). All chemical shifts values (d) are reported in parts per million (ppm), using the residual solvent signal (2.49) of DMSO-d 6 as reference. Absorption spectra were recorded at 25˚C with a Hitachi U-3000 spectrophotometer (Hitachi, Ltd., Tokyo, Japan). (1) p-Nitroaniline (2.0 g, 14 mmol) was dissolved in ethanol-triethylamine (dried over molecular sieves 4A, 220 ml) and a solution of methyl isothiocyanate (9.1 g, 124 mmol) in ethanol (5 ml) was added slowly. The reaction solution was stirred for 47 h at 80˚C, and then the solvent was evaporated. Repeated recrystallization from ethanol gave the product as pale yellow crystals (0.30 g; 10% H, 4.29; N, 19.89; S, 15.18. Found: C, 45.42; H, 4.28; N, 19.60; S, 14.88. Synthesis of N-methyl-N´-(4-nitrophenyl)thiourea Results and DiscussionThe spectral characteristics o...

Enhanced Anion Binding from Unusual Coordination Modes of Bis(thiourea) Ligands in Platinum Group Metal Complexes

“…[28] A fluorescent anion sensor based on a pyrene electron acceptor linked to a thiourea donor and a colorimetric sensor based on p-nitrophenylthiourea have been prepared. [29,30] Gunnlaugsson and co-workers have developed similar chemosensors for anions by using anthracene-based fluorescent sensors. [20,31,32] Other examples of recently synthesised thiourea sensors include hosts with the thiourea group linked to fluorescent sensor moieties by a rigid hydrazine spacer selective for acetate, [33][34][35][36] Hosts based on coumarin sensors that act as both fluorescent and colorimetric sensors [37] and compounds that utilise cooperativity between the thiourea group and an amine group adjacent to a naphthalimide sensor are also known.…”

Effect of Intramonolayer Hydrogen Bonding of Carboxyl Groups in Self-assembled Monolayers on a Single Force with Phenylurea on an AFM Probe Tip

“…For example, high stability constants of (thio)urea derivatives bearing a variety of substituents with hydrophilic anions, such as H2PO4 -, have been previously reported. [51][52][53][54] Their hydrogen-bonding abilities can also afford their use as organic gelators. [46][47][48][49] A phenylurea-modified tip (PhUET-tip) was used to measure the adhesion force on the COOH-terminated SAM (MHA-SAM) surface.…”

“…Recently, the hydrogenbonding ability of (thio)urea compounds has received considerable attention, and has been utilized to develop highly functionalized novel materials, such as organic gelators, [46][47][48][49] and synthetic receptors for hydrophilic anions, 50 including H2PO4 -, [51][52][53][54] halide, [55][56][57][58][59][60] and ATP. 61 It has been reported that the silica nanosphere catalyst, functionalized with a urea derivative (i.e., ureidopropyl group), can activate the carbonyl compound, a reaction substrate for its catalytic reactions, based on the urea's hydrogen-bonding ability.…”

Application of Gold Nanoparticles to Spectrophotometric Sensing of Hydrophilic Anions Based on Molecular Recognition by Urea Derivative

“…Thus, a variety of these artificial host molecules with specific hydrogenbonding ability have been reported for sensing hydrophilic anions. [1][2][3][7][8][9][10][11][12][13][14] As mentioned above, anion recognition under aqueous conditions, and therefore effective sensing systems of hydrophilic anions, are still challenging to study. This difficulty in anion sensing can be ascribed to the low charge density, geometrical variety, and high hydration energy of anions.…”