Selective fluorescence sensor based on ion-imprinted polymer-modified quantum dots for trace detection of Cr(VI) in aqueous solution.

A new fluorescence sensor (QDs-IIP), based on ion-imprinted polymers (IIP) as recognition element and Mn-doped ZnS quantum dots (QDs) as fluorophore, was synthesized for the selective and sensitive determination of hexavalent chromium (Cr(VI)) ions. The QD was first coated by SiO2 layer, and then modified with Cr(VI)-imprinted polymer. Several parameters affecting fluorescence intensity such as tetraethylorthosilicate (TEOS) volume, ZnS:Mn@SiO2 amount, and radiation time were investigated and optimized. The QDs-IIP was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). Furthermore, the fluorescence quenching mechanism was investigated by using UV-VIS and fluorescence spectrophotometer, and it was found that internal filtration effect was the main fluorescence quenching mechanism. The relative fluorescence intensity (F0/F) increased linearly with the increase of Cr(VI) concentration in the range of 20 µg L-1-1.0 mg L-1. The QDs-IIP sensor showed high recognition selectivity for Cr(VI) in comparison with the QDs-NIP sensor with an imprinting factor (IF) of 2.53, and it could be reused 5 times. In addition, an analytical method of Cr(VI) based on the QDs-IIP sensor was established with a limit of detection of 5.48 µg L-1, and was then applied to actual water samples with satisfactory results. Therefore, QDs-IIP can be deemed as a practicable fluorescent sensor for trace Cr(VI) detection. Graphical abstract.

Determination of dopamine hydrochloride by host-guest interaction based on water-soluble pillar[5]arene.

The supramolecular interaction between the water-soluble pillar[5]arene (WP[5]) as host and dopamine hydrochloride (DH) as guest was studied by spectrofluorometry. The fluorescence intensity of DH gradually decreased with increasing WP[5] concentration, and the possible interaction mechanism between WP[5] and DH was confirmed by 1H NMR, 2D NOESY, and molecular modelling. Based on significant DH fluorescence, a highly sensitive and selective method for DH determination was developed for the first time. The fluorescence intensity was measured at 312nm, with excitation at 285nm. The effects of pH, temperature, and reaction time on the fluorescence spectra of the WP[5]-DH complex were investigated. A linear relationship between fluorescence intensity and DH concentration in the range of 0.07-6.2µgmL-1 was obtained. The corresponding linear regression equation is ΔF=25.76 C+13.56 (where C denotes the concentration in µgmL-1), with the limit of detection equal to 0.03µgmL-1 and the correlation coefficient equal to 0.9996. This method can be used for the determination of dopamine in injection and urine samples. In addition, the WP[5]-DH complex has potential applications in fluorescent sensing and pharmacokinetics studies of DH.

The mechanisms for N-heterocyclic olefin-catalyzed formation of cyclic carbonate from CO2 and propargylic alcohols.

The mechanistic details of N-heterocyclic olefin-catalyzed formation of cyclic carbonate from CO2 and propargylic alcohols were investigated by DFT calculations. Six mechanisms, four for the formation of five-membered cyclic carbonate (M-A, M-B, M-B' and M-C), and two for six-membered cyclic carbonate (M-D and M-E), were fully investigated. The energy profiles in dichloromethane showed that M-B is the predominant reaction with the lowest barrier of 31.99 kcal mol(-1), while M-C and M-D may be kinetically competitive to M-B. The very high activation energy of 45.37 kcal mol(-1), 57.07 kcal mol(-1) and 59.61 kcal mol(-1) for M-A, M-B' and M-E, respectively, suggest that they are of lesser importance in the overall mechanism.

N,N'-Bis(4-nitro-phen-yl)biphenyl-2,2'-dicarboxamide.

In the title compound, C(26)H(18)N(4)O(6), the amide units are approximately coplanar with the benzene ring bonded to the N atom [dihedral angles of 10.59 (10) and 24.00 (12)°], but twisted significantly out of the plane of the benzene ring bonded to the carbonyl C atom [dihedral angles of 57.82 (9) and 58.05 (9)°]. The dihedral angle between the two rings of the biphenyl unit is 77.66 (4)°. Intra-molecular N-H⋯O hydrogen bonds and weak C-H⋯O inter-actions occur. The crystal structure is stabilized by inter-molecular N-H⋯O hydrogen bonds and C-H⋯O contacts.

N,N'-Bis(2-methoxy-phen-yl)biphenyl-2,2'-dicarboxamide.

In the title compound, C(28)H(24)N(2)O(4), the dihedral angle between the two rings of the biphenyl unit is 75.34 (9)°. The outer aromatic rings form dihedral angles of 66.96 (1) and 85.69 (8)° with the rings to which they are attached . The mol-ecular structure is stabilized by intra-molecular C-H⋯O and N-H⋯O hydrogen bonds. In the crystal structure, inter-molecular N-H⋯O inter-actions are observed.

9,10-Bis{2-[1-(2-pyridylmeth-yl)imidazolium-3-yl]eth-oxy}anthracene bis(hexa-fluoridophosphate).

The cation of the title compound, C(36)H(34)N(6)O(2) (2+)·2PF(6) (-), lies across a crystallographic inversion centre. The imidazole and pyridine rings form dihedral angles of 82.28 (5)° and 11.87 (7)°, respectively, with the anthracene ring system. The crystal packing is stabilized by π-π inter-actions between the pyridine ring and the central ring of anthracene, with a ring centroid-centroid distance of 3.684 (3) Å. The PF(6) (-) anion is disordered over three different positions with occupancies of 0.284 (6), 0.354 (8) and 0.362 (9).