Analytical Sciences

The 1H{19F} saturation transfer difference (STD) experiment presented here incorporates the WATERGATE W5 sequence to observe protein–ligand interactions in a human serum albumin (HSA)-fleroxacin complex. In conventional STD experiments, 1H of proteins are first saturated, and the ligands bound to these proteins are then observed. The method proposed here reverses this process: fluorine atoms in fleroxacin are selectively saturated, and saturation transfer then occurs to protons of fleroxacin as well as to those of HSA. The combined use of the present 1H{19F} STD and conventional STD methods is expected to provide better insight in the analysis of the role of fluorine atoms in a fluorinated compound.

Local crystalline structures of LiCoO2 nanothin film cathodes in a lithium ion battery have been spectroscopically elucidated through confocal Raman imaging analysis at high spatial resolution of several hundred nanometers. A significant difference in the crystalline structure is found between the nanometric thin films and bulk powders. Thermally induced local decomposition of LiCoO2 into an impurity phase on the films has also been revealed along with the mechanism of the temperature-triggered decomposition process. Moreover, frequency-based Raman imaging enables us to locally probe spatial separation between stoichiometric (LiCoO2) and non-stoichiometric (Li1-xCoO2, 0 < x < 1) crystal phases on the thin films. Such local crystalline analysis is a promising approach to provide new insights into the degradation mechanism of lithium-ion batteries, which would result in improving the performance of thin film-based lithium ion batteries.

Nanoparticles of cadmium telluride coated with mercaptoacetic acid were prepared in the water phase. Further, an assay of lysozyme with a sensitivity at the nanogram level is proposed. At pH 7.28, lysozyme with positive charges can interact with CdTe nanoparticles. The resonance light-scattering (RLS) signals of functionalized nano-CdTe were greatly enhanced by lysozyme in the region of 300 - 600 nm, characterized with peaks located at 367, 470 and 533 nm. A linear relationship could be established between the enhanced RLS intensity and the lysozyme concentration in the range of 0.06 - 4.0 μg mL-1. The limit of detection was 9.5 ng mL-1. The contents of lysozyme were determined with recoveries of 95.6 - 104.8% and RSD of 1.5 - 2.3%, respectively. This method is sensitive, rapid, accurate and simple, and provides a new and reliable means for the quantity determination of lysozyme.

A number-average molecular weight measurement was tested as a direct and simple method for the confirmation of polymerization of the metal complex in organic solvent. This method was applied to the complexes of thallium(I), lead(II) and nickel(II) with O.O’-dialkyl dithiophosphates (alkyl groups=methyl, ethyl, propyl and butyl) in benzene, chloroform and acetonitrile. In the cases of lead(II) and nickel(II) complexes, the number-average molecular weight in any solvent did not depend on the concentration of these complexes, while it agreed with the molecular weight of each monomer of these complexes. On the other hand, the magnitude of the number-average molecular weight for thallium(I) complexes increased with increasing the concentration of the complex but did not go up to beyond twice the molecular weight of monomer in any solvent. The dimerization constants of thallium(I) complexes were obtained by analyzing the relationship between the number-average molecular weight and the concentration of the complex. The values of dimerization constants were little affected by the alkyl group in the ligand. But the values were affected by solvents and became smaller in the order: chloroform, benzene and acetonitrile.

A highly sensitive and selective fluorescence method of quantitative detection for mercury in soil was developed using non-labeled molecular beacon (MB), single-stranded nucleic acid (ssDNA) and fluorescent dye Hoechst 33258. In this analytical method, the loop of MB was designed to be a sequence that was complementary to the ssDNA with multiple T-T mismatches, the stem of MB was completely designed as C-G base pairs, and both ends of the MB are not modified by any fluorophore and quencher. In the absence of Hg2+, the interaction between Hoechst 33258 and the MB was very weak, and the fluorescence signal of Hoechst 33258 was very low. In the presence of Hg2+, the MB and ssDNA with multiple T-T mismatches formed a double-stranded nucleic acid (dsDNA) via the T-Hg2+-T coordination structure which provided binding sites for Hoechst 33258. Then Hoechst 33258 binded to A-T base pairs of dsDNA, and the fluorescence intensity of Hoechst 33258 was significantly enhanced. Thus, a highly sensitive fluorescence quantitative detection method for Hg2+ can be realized. In this strategy, the optimal determination conditions for Hg2+ were a buffer solution pH of 8.2, an incubated temperature of 50°C, an incubated time of 5 min and NaCl of 60 mmol L−1. Under the optimum conditions, the fluorescence intensity of Hoechst 33258 exhibited a good linear dependence on the concentration of Hg2+ in the range of 5 × 10−9 − 400 × 10−9 mol L−1. The fitted regression equation was ΔI = 2.1084C − 8.9587 with a correlation coefficient of 0.9943 (R2), and the detection limit of this method was 3 × 10−9 mol L−1 (3σ). The proposed method had a high selection; the common substances in soil such as Ca2+, Mg2+, Mn2+, Fe3+, Cu2+, Pb2+, Al3+, K+, Na+, Ni2+, Cd2+, Cr3+, SiO32−, Cl−, PO43−, NH4+ and S2− had no interference to the detection of mercury. The proposed method had a high accuracy, and it was applied to detect mercury of ten different types of soil; the recoveries were 97.65–103.22%. In addition, the proposed method had a low background emission, fast detection speed and low detection cost.

Icaritin (ICT), a major component in herb Epimedium brevicornum Maxim., shows beneficial effects for the treatment of osteoporosis and various cancers, and is predominantly metabolized to glucuronidated icaritin (GICT). Although clinical trials of ICT have exhibited good safety and tolerance, the dynamic bioditributions of ICT and GICT have not been reported. In the present study, the chemical structure of GICT was firstly reported, and a reliable ultra-high performance liquid chromatography-tandem mass spectrometry method (UHPLC-MS/MS) was firstly established for the simultaneous quantifications of ICT and GICT in rat tissues. The dynamic distribution of ICT and GICT in rat tissues and their pharmacokinetic parameters have been reported for the first time. ICT, GICT and the internal standard coumestrol were separated on a C18 column with a gradient mobile phase of acetonitrile and water containing ammonium formate and formic acid at a flow rate of 0.3 mL min−1. The analytes were quantified by a triple quadrupole tandem mass spectrometer in the negative ionization mode. The lower limit of quantification values for ICT and GICT were 0.2 and 2 ng mL−1, respectively. Good selectivity, linearity, accuracy, precision and recovery were achieved, and no significant matrix effect was observed. The UHPLC-MS/MS was firstly applied to a dynamic biodistribution study of ICT and GICT in rats, following an intraperitoneal administration of ICT at a dose of 10 mg kg−1.