Tris(hydroxymethyl)aminomethane, 2-pyridinecarboxaldehyde were purchased from Tokyo Chemical Industry Co., Ltd. Sodium hydroxide (Mallinckrodt), 37% w/w hydrochloric acid (Italmar) were analytical grade. All metal salts (LiCl, NaOAc, KCl, CsBr, Ca(OAc)2, Ba(ClO4)2, Al2(SO4)3, Pb(OAc)2·3H2O, Co(OAc)2·4H2O, NiCl2·6H2O, CuI, Cu(OAc)2·H2O, AgNO3, Zn(OAc)2·2H2O and Cd(OAc)2·2H2O were purchased from Chemical Express and used as received. Hg(OAc)2 and Ce(OAc)3·2H2O were available from QRëC Chemical Co., Ltd. and Tokyo Chemical Industry Co., Ltd., respectively. Ethanol was used without further purification from Quality Reagent Chemical Co., Ltd. De-ionized (DI) water was obtained from Nanopure® Analytical Deionization Water with an electric resistance ≥18.2 MΩ/cm.
1H NMR and 13C NMR spectra of the compound were acquired on a Bruker AVANCE 400 MHz in CD3OD with tetramethylsilane (TMS) as an internal standard. The UV-visible spectrophotometer was carried out on BIOCHROM Model Libra S80. HORIBA Model Fluor Max 4P was used to measure a fluorescent value and activation energy at wavelength 270 nm recorded in a range of 300 – 450 nm. HR-ESI mass spectrum was measured on a Bruker Micro TOF spectrometer. Frequency range 4000 to 400 cm−1 infrared result (IR) was obtained on a JASCO Model FT/IR-4100 spectrophotometer with KBr pellet and Bruker Hong Kong Limited model ALPHA.
2.1 2-(pyridin-2-yl)oxazolidine-4,4-diyl)dimethanol (TN)
A synthetic route of the oxazolidine derivative for fluorescent probe was showed in Scheme 1. To a solution of tris(hydroxymethyl)aminomethane (1.21 g, 10.0 mmol) in ethanol (10 cm3) in a round-bottomed flask equipped with a stir bar, a solution of 2-pyridinecarboxaldehyde (0.95 g, 10.0 mmol) in ethanol (10 cm3) was slowly added. The solution mixture was refluxed under boiling temperature of ethanol for 4 hours. The resulting product was purified by column chromatography on silica gel with ethyl acetate/petroleum ether (60:40 v/v) as mobile phase. The expected product was separated after removing out of organic solvent in vacuo and freeze-dried for 3 hours. The pale yellow solid was obtained in high purity (1.53 g, 82%). 1H NMR (CD3OD, 400 MHz) ppm δ 8.58 (d, J = 4.0 Hz, 1H, CH=N in pyridine), 7.89 (t, J = 8.0 Hz, 1H, CH in pyridine ring), 7.61 (d, J = 8.0 Hz, 1H, CH in pyridine ring), 7.42 (dd, J = 8.0, 4.0 Hz, 1H, CH in pyridine ring), 5.52 (s, 1H, O–CH–N), 3.90 – 3.83 (m, 2H, CH2), 3.71 – 3.61 (m, 4H, CH2OH), 2.06 (s, 1H, NH). 13C NMR (CD3OD, 100 MHz) δ 157.1 (Cq=C), 148.6 (C=C), 137.5 (C=C), 124.1 (C=C), 122.0 (C=C), 91.7 (O–C–N), 69.5 (Cq), 67.2 (O–C–C), 63.0 (C–OH), 62.4 (C–OH). FTIR (KBr) cm–1 3342, 3274, 2934, 2878, 1651, 1596, 1460, 1436, 1042, 772, 750, 692, 618. HRMS-ESI-TOF m/z 211.1183 [M+H]+ (calcd for C10H15N2O3, 211.1983).
2.2 DFT calculations
Tridentate based-oxazolidine (TN) and its coordination of cerium(III) (TN-Ce3+) were performed by using the density functional theory (DFT) with the B3LYP level of theory, Becke’s three-parameter (B3) [21] nonlocal exchange with the correlation functional of Lee, Yang, and Parr (LYP) [22]. B3LYP level has been utilized widely to predict molecular geometries, estimate HOMO-LUMO energy gaps, and, propose a coordination complex with the metal ions [20, 23-25]. DFT calculations were carried out at the B3LYP/6-31G(d,p) [26] level for C, N, O, and H atoms, except the Ce atom, which was described by using the Stuttgart/Dresden effective core potential (SDD) basis set [27]. The solvent effects were simulated in the water phase using the polarizable continuum model (PCM). All computations were carried out by using the Gaussian09 suite of programs [28].