Synthesis and properties of novel polyurethanes containing 3,4‐dioxybenzylidenecyanoacetate group as a nonlinear optical chromophore

Methyl 3,4‐di‐(2′‐hydroxyethoxy)benzylidenecyanoacetate ( 3 ) was prepared by hydrolysis of methyl 3,4‐di‐(2′‐vinyloxyethoxy)benzylidenecyanoacetate ( 2 ). Diol 3 was condensed with 2,4‐toluenediisocyanate, 3,3′‐dimethoxy‐4,4′‐biphenylenediisocyanate, and 1,6‐hexamethylenediisocyanate to yield polyurethanes 4 – 6 containing the nonlinear optical chromophore 3,4‐dioxybenzylidenecyanoacetate. The resulting polyurethanes 4 – 6 were soluble in common organic solvents such as acetone and dimethylformamide. Polymers 4 – 6 indicated thermal stability up to 300 °C in thermogravimetric thermograms with glass‐transition temperature values obtained from differential scanning calorimetric thermograms in the range of 78–102 °C. The second‐harmonic generation coefficients (d₃₃) of the poled polymer films were around 6.9 × 10^?9 esu. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1742–1748, 2002     

Determination of gold in geological samples by x-ray fluorescence spectrometry after extraction with tributyl phosphate

The behaviour of gold and elements impeding its x-ray fluorescence spectrometric (XRF) determination, namely zinc, lead and arsenic, was studied during their extraction from hydrochloric acid, nitric acid, and aqua regia solutions using tributyl phosphate as a solid extractant [SE(TBP)]. Extraction of gold from pulps after aqua regia leaching was found to be the most favourable approach for the quantitative and selective recovery of gold. The gold distribution ratio, D_Au, is ca. 10⁴ ml g^?1. For extraction from hydrochloric acid solutions the D_Au value also exceeds 10⁴ in the whole range of gold concentrations studied (10^?8?10^?4 M), but it decreases substantially with increasing extraction temperature, from 5 × 10⁵ ml g^?1 at 20°C to 9 × 10³ ml g^?1 at 70°C. An anomalously high distribution ratio of lead, D_Pb ≈ 10³ ml g^?1, was observed during extraction from hydrochloric solutions in the presence of chlorine. This could be explained by the formation of the chloro complexes of lead(IV). An XRF method for the determination of gold in natural samples was developed, which includes back-extraction of gold from SE(TBP) using a hot 0.025 M thiourea solution, providing a thin sample layer for secondary XRF. For 25 g of sample material the limit of determination is 10 ng g^?1 (10^?6%). The accuracy of the technique was checked using different reference materials. The results agreed within 10%.     

火焰原子吸收光谱法测定茶叶中的锰

介绍悬浮液进样-次灵敏线火焰原子吸收光谱法测定茶叶中的锰的方法。以琼脂为悬浮剂，将茶叶样品均匀、稳定地悬浮于琼脂溶胶中，直接喷入空气-乙炔火焰中，利用锰280.1nm次灵敏线，以工作曲线或标准加入法测定锰的含量，方法简便、快速，用于测定茶叶和桃叶样品中的锰，结果准确。     

硒芳香杂环化合物的光谱和电化学性质

用紫外光谱，荧光光谱和循环伏安法研究了含硒芳香杂环化合物（苤硒脑）在不同溶剂中的谱学和电化学性质，对不同分子结构或取代基的苤硒脑化合物的性质进行了比较，并初步探讨了溶剂对苤硒脑化合物谱学性质的影响规律。     

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between heptamethylene cyanine and Alcian blue 8GX

A new method based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic heptamethylene cyanine (HMC) and a polycationic phthalocyanine dye, Alcian blue 8GX, is presented for the determination of nucleic acids. With a maximum excitation wavelength at 766 nm and a maximum emission wavelength at 796 nm, the fluorescence recovery is linear with the concentration of nucleic acids added. Factors including the acidity of the medium, the reaction time, the optimal ratio of the two reagents, as well as the influence of foreign substance were all investigated. Meanwhile, the mechanism of fluorescence recovery was also studied. Under the optimal conditions, the linear ranges of the calibration curves were 10-250 ng ml⁻¹ for calf thymus DNA (CT DNA) and 10-200 ng ml⁻¹ for yeast RNA. The detection limits were 6.8 ng ml⁻¹ for CT DNA and 6.3 ng ml⁻¹ for yeast RNA, respectively. The method has been applied to the analysis of practical samples and the recovery results were satisfactory.     

Thermodynamic properties of the gaseous barium silicates BaSiO2 and BaSiO3

In the present study, the stability of gaseous barium silicates was confirmed by the high temperature mass spectrometry. On the basis of equilibrium constants measured for gas-phase reactions, the standard formation enthalpies were determined for gaseous barium silicates as (−510 ± 15) kJ · mol⁻¹ and (−884 ± 18) kJ · mol⁻¹ at 298 K; standard atomization enthalpies as (1637 ± 17) kJ · mol⁻¹ and (2318 ± 20) kJ · mol⁻¹ at 298 K for BaSiO₂ and BaSiO₃, respectively. Based on the results obtained the critical analysis of the literature data was carried out.     

Effects of different alkali metal ions on the cationization of poly(ethylene glycol)s in matrix-assisted laser desorption/ionization mass spectrometry: a new selectivity parameter

The cationization of poly(ethylene glycol)s, PEG 4000 and PEG 6000, under matrix-assisted laser desorption/ionization conditions was studied by using different concentration ratios of the sodium ion, as the reference ion, and another alkali metal ion (Li(+), K(+), Rb(+), Cs(+)). A linear correlation was found between the intensity ratio of the sodiated PEGs and PEGs cationized with alkali metal ions versus the initial concentration ratio of sodium and alkali metal ions. The slopes of these straight lines are proposed as a novel selectivity ratio for the ionization process. The intensity distribution of the cationized PEGs was also investigated. It was found that the cationized oligomers follow Poisson statistics. The M(n) and M(w) values were also evaluated. An explanation for the observed effects is given.     

Determination of Glimepiride in Human Plasma by LC-MS-MS and Comparison of Sample Preparation Methods for Glimepiride

A sensitive and selective method for quantitation of glimepiride in human plasma was established using liquid chromatography-electrospray ionization tandem mass spectrometry. Three different methods for the sample preparation of glimepiride and an internal standard were investigated (liquid-liquid extraction, solid-phase extraction and protein precipitation). Glipizide was used as an internal standard. Compounds were separated on a C₁₈ column with 80% acetonitrile and 20% deionized water (adjusted to pH 3.5 with acetic acid), as mobile phase at a flow rate of 200 L min^–1. By use of multiple reaction monitoring mode in MS-MS with liquid-liquid extraction and solid-phase extraction, glimepiride and glipizide were detected without severe interference from the human plasma matrix. Glimepiride produced a protonated precursor ion ([M+H]⁺) at m/z 491 and a corresponding product ion at m/z 352, and the internal standard produced a protonated precursor ion ([M+H]⁺) at m/z 446 and a corresponding product ion at m/z 321. The limit of quantitation was 0.1 ng mL^–1, 0.5 ng mL^–1 and 1.0 ng mL^–1 when using liquid-liquid extraction, solid-phase extraction and protein precipitation, respectively. The validation, reproducibility, stability, and recovery of the different sample preparation methods were comparable and all the methods gave reliable results. The method has been successfully applied to pharmacokinetic study of glimepiride in human plasma.     

Improved Fluorometric DNA Determination Based on the Interaction of the DNA/Polycation Complex with Hoechst 33258

When DNA is mixed with the cationic polyelectrolyte poly(diallyldimethyl ammonium chloride) (PDDA), the DNA/PDDA complex is formed instantaneously at room temperature. This complex is much more efficient in enhancing the fluorescence of Hoechst 33258 (H 33258) than DNA alone. Based on the interaction of H 33258 with the DNA/PDDA complex, a new fluorescence assay for DNA is described. At pH 7.3 in Tris-HCl buffered solution, the DNA/PDDA complex causes a sharp enhancement in fluorescence intensity of H 33258. Simultanously, the emission maximum wavelength of H 33258 blueshifts from 490nm to 450nm, while the excitation redshifts from 345 to 350nm. The calibration graphs for calf thymus DNA (ctDNA) and herring sperm DNA (hsDNA) are both linear up to 5.0µgmL^–1 when the concentration of H 33258 and PDDA are fixed at 1.5×10^–6 and 1.6×10^–5molL^–1, respectively. The method is specific for native DNA. The 3 detection limits for ctDNA and hsDNA are 1.8 and 5.6ngmL^–1, respectively, i.e. much lower than in the presence of H 33258 alone. Four synthetic samples were determined satisfactorily. This method can also be developed to investigate the formation and the nature of the complexes between DNA and polycations, which have recently been widely applied in some fields such as genetic engineering and gene therapy.     

Synthesis and Electrospray Ionization Mass Spectra of N-（1,3, 2-Dioxaphosphorinan-2-ylmethyl）thiophosphoramidates

N-（1,3,2-Dioxaphosphorinan-2-ylmethyl）thiophosphoramidates were synthesized and determined by NMR spectra and positive ion electrospray ionization mass spectrometry （ESI-MS） in conjunction with tandem mass spectrometry （MS/MS）. The fragmentation pathways were investigated. The results show that these characteristic ions in ESI mass spectra are useful in the structural determination of N-（1,3,2-dioxaphosphorinan-2-ylmethyl）- thiophosphoramidates.