Synthesis and characterization of fluorescent starch using fluorescein as fluorophore: potential polymeric temperature/pH indicators

A convenient method for attaching fluorescein (via its epoxy derivate) to natural starch and its temperature/pH‐sensitive qualities of fluorescence were investigated. 3‐epoxypropoxy fluorescein (EPF) was first synthesized through the reaction between fluorescein and epichlorohydrin, and starch‐bearing fluorescein (ST‐EPF) was prepared via ring‐opening reaction with EPF in dimethyl sulfoxide (DMSO) solution, in the presence of NaH as a catalyst. Both of them were characterized by the methods of ¹H NMR, MS, IR, XRD, UV–Vis, and luminescence spectra, respectively. The chemiluminescent and photophysical behaviors of the dye fluorescein derivative and the polymer‐containing fluorescein were studied. The results indicated that ST‐EPF could still provide temperature and pH sensitivity similar to that of fluorescein and could achieve better long‐term stability and fast equilibrium response. ST‐EPF had an excellent linear response between relative fluorescence intensity and temperature in the range of 0–60°C and a nonlinear relationship between relative fluorescence intensity and pH in the wide range of 0.0–12.0, and so it has promise as an optical transducer for temperature and pH value determinations. Copyright © 2008 John Wiley & Sons, Ltd.     

Structure elucidation and NMR spectral assignments of three new lignan glycosides from Akebia trifoliata

Three new lignan glycosides (1-3) were isolated from the stems of Akebia trifoliata. Their structures were elucidated as (7R,8R,7'R,8'R)3,3',5,5'tetramethoxy-4,4'dihydroxy-7,9':7',9-diepoxylignan-4-O-beta-D-glucopyranoside (1), (7S,8S,8'R)-4,4',9-trihydroxy-3,3',5,5'-tetramethoxy-7,9'-epoxylignan-7'-one 9-O-beta-D-glucopyranoside (2), (7R,8R,8'S)-4,4',9-trihydroxy3,3',5,5'-tetramethoxy-7,9'-epoxylignan-7'-one 9-O-beta-D-glucopyranoside (3) by spectral analyses, primarily NMR, MS and CD. The NMR assignments for the compounds were carried out using 1H, 13C, DEPT, COSY, HSQC, HMBC and ROESY NMR experiments.     

湛江市几种蔬菜的营养成分分析

对湛江产芥菜,芫荽和麦菜的微量元素,氨基酸进行了定量分析。结果表明营养元素如Ｃｕ、Ｚｎ、Ｆｅ、Ｃａ、Ｍｇ、Ｋ、Ｍｎ、Ｎａ等的含量较丰富,也含有多种人体必需的氨基酸,但共同的特征是均缺乏赖氨酸。     

V2O5电致变色薄膜的Raman光谱

近年来,通过向过渡金属氧化物薄膜注入Ｌｉ 制作可调节光透过率的电变色器件已越来越引起广泛的重视[1、2].由于Ｖ2Ｏ5薄膜的稳定性差,限制了它在实际中的应用.因此,为了获得变色效率高、稳定性和可逆性能好的Ｖ2Ｏ5薄膜,使用了多种制备方法,如磁控溅射法[3、6]、电化学沉积法[7、8]、溶胶凝胶法[9、10]、旋涂法[11、12]、真空蒸镀法[13、14]等.但是,无论那种方法都要解决Ｖ2Ｏ5本身在Ｈ2Ｏ或醇等的电解质溶液中电致变色时的溶解问题,通常采用控制薄膜的沉积温度或者退火处理来提高薄膜的电致变色性能[3、4、11].为了探明薄膜结构与电致变色…     

Reversible redox-switchable second-order optical nonlinearity in polyoxometalate: a quantum chemical study of [PW11O39(ReN)]n- (n = 3-7)

In this paper, the relationship between the reversible redox properties and the second-order nonlinear optical (NLO) responses for the title series of complexes has been systematically investigated by using the time-dependent density functional theory (TDDFT) method combined with the sum-over-states (SOS) formalism. The results reveal that the successive reduction processes of five PW11ReN redox states should be PW11ReVII (1) --> PW11ReVI (2) --> PW11ReV (3) --> PW11ReV1e ( 4) --> PW 11ReV2e (5). Furthermore, their electrochemical properties have been reproduced successfully. It is noteworthy that the second-order NLO behaviors can be switched by reversible redox for the present studied complexes. Full oxidation constitutes a convenient way to switch off the second-order polarizability (system 1). The incorporation of extra electrons causes significant enhancement in the second-order NLO activity, especially for the third reduced state (system 4), whose static second-order polarizability (betavec) is about 144 times larger than that of fully oxidized 1. The characteristic of the charge-transfer transition corresponding to the dominant contributions to the betavec values indicates that metal-centered redox processes influence the intramolecular donor or acceptor character. Therefore, these kinds of complexes with the facile and reversible redox states could become excellent switchable NLO materials.     

MALDI linear-field reflectron TOF post-source decay analysis of underivatized oligosaccharides: Determination of glycosidic linkages and anomeric configurations using anion attachment

Six different anionic species (fluoride, chloride, bromide, iodide, nitrate, and acetate) are tested for their abilities to form anionic adducts with neutral oligosaccharides that are detectable by MALDI-TOF mass spectrometry. Fluoride and acetate cannot form anionic adducts with the oligosaccharides in significant yields. However, bromide, iodide, and nitrate anionic adducts consistently appear in higher abundances relative to [M - H](-), just like the highly stable chloride adducts. Post-source decay (PSD) decompositions of Br(-), I(-), and NO(3)(-) adducts of oligosaccharides provide no structural information, i.e., they yield the respective anions as the main product ions. However, determination of linkage types is achieved by analysis of structurally-informative diagnostic peaks offered by negative ion PSD spectra of chloride adducts of oligosaccharides, whereas the relative peak intensities of pairs of diagnostic fragment ions allow differentiation of anomeric configurations of glycosidic bonds. Thus, simultaneous identification of the linkage types and anomeric configurations of glycosidic bonds is achieved. Our data indicate that negative ion PSD fragmentation patterns of chloride adducts of oligosaccharides are mainly determined by the linkage types. Correlation may exist between the linkage positions and fragmentation mechanisms and/or steric requirements for both cross-ring and glycosidic bond fragmentations. PSD of the chloride adducts of saccharides containing a terminal Glcalpha1-2Fru linkage also yields chlorine-containing fragment ions which appear to be specifically diagnostic for a fructose linked at the 2-position on the reducing end. This also allows differentiation from saccharides with a 1-1 linked pyranose on the same position.     

Analysis of fatty acids in sputum from patients with pulmonary tuberculosis using gas chromatography–mass spectrometry preceded by solid-phase microextraction and post-derivatization on the fiber

A method based on solid-phase microextraction (SPME) and post-derivatization on the fiber coupled to gas chromatography–mass spectrometry (GC–MS) was developed for the analysis of fatty acids in sputum from patients with pulmonary tuberculosis. The sputum specimens were digested, hydrolyzed, extracted, derivertized, injected and analyzed without cultivation or isolation of the microorganism. Under optimized conditions, the relative standard deviations (RSD, n = 5) for all analytes were below 17% and the limits of detection varied from 1.68 (C_24:0) to 150.4 μg L⁻¹ (C_12:0). Good linearity was observed for all the fatty acids studied except for C_12:0 within a wide concentration range of three orders of magnitudes with the correlation coefficients ranging from 0.91 (C_24:0) to 0.99 (C_14:0). Fatty acids in sputum specimens from 21 persons were directly analyzed using the proposed method. The results show that in all the sputum specimens from patients, who were clinically diagnosed with tuberculosis (TB), tuberculosis stearic acid (TBSA) was detected, while in all the sputum samples from persons without TB, TBSA was not found. The possibility of using the proposed method to detect mycobacterium tuberculosis (MTB) via the identification of TBSA in sputum was discussed. The comparison with other methods including sputum culture and microscopy of direct smears indicated that the proposed method is fast and sensitive for the analysis of fatty acids in sputum and offers an alternative for the detection of MTB in sputum.     

Synthesis and characterization of a novel complex [Pd(Bipy)2](Bpcc) · 11H2O

The complex [Pd(Bipy)₂](Bpcc) · 11H₂O has been synthesized and characterized (Bipy = 2,2′-bipyridyl, H₂Bpcc = 4,4′-biphenylcarboxylic acid). The supramolecular architecture was constructed through hydrogen bonding and π-π-stacking. The Pd atom is four-coordinated and forms a distorted square geometry. The free H₂O molecules form 1D infinite zigzag chains of water cluster, while the water cluster and Bpcc^2? form an organic-water framework.     

A Time‐Resolved Spectroscopic Study of the Bichromophoric Phototrigger 3′,5′‐Dimethoxybenzoin Diethyl Phosphate: Interaction Between the Two Chromophores Determines the Reaction Pathway

3′,5′‐Dimethoxybenzoin (DMB) is a bichromophoric system that has widespread application as a highly efficient photoremovable protecting group (PRPG) for the release of diverse functional groups. The photodeprotection of DMB phototriggers is remarkably clean, and is accompanied by the formation of a biologically benign cyclization product, 3′,5′‐dimethoxybenzofuran (DMBF). The underlying mechanism of the DMB deprotection and cyclization has, however, until now remained unclear. Femtosecond transient absorption (fs‐TA) spectroscopy and nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopy were employed to detect the transient species directly, and examine the dynamic transformations involved in the primary photoreactions for DMB diethyl phosphate (DMBDP) in acetonitrile (CH₃CN). To assess the electronic character and the role played by the individual sub‐chromophore, that is, the benzoyl, and the di‐meta‐methoxybenzylic moieties, for the DMBDP deprotection, comparative fs‐TA measurements were also carried out for the reference compounds diethyl phosphate acetophenone (DPAP), and 3′,5′‐dimethoxybenzylic diethyl phosphate (DMBnDP) in the same solvent. Comparison of the fs‐TA spectra reveals that the photoexcited DMBDP exhibits distinctly different spectral character and dynamic evolution from those of the reference compounds. This fact, combined with the related steady‐state spectral and density functional theoretical results, strongly suggests the presence in DMBDP of a significant interaction between the two sub‐chromophores, and that this interaction plays a governing role in determining the nature of the photoexcitation and the reaction channel of the subsequent photophysical and photochemical transformations. The ns‐TR³ results and their correlation with the fs‐TA spectra and dynamics provide evidence for a novel concerted deprotection–cyclization mechanism for DMBDP in CH₃CN. By monitoring the direct generation of the transient DMBF product, the cyclization time constant was determined unequivocally to be ≈1 ns. This indicates that there is little relevance for the long‐lived intermediates (>10 ns) in giving the DMBF product, and excludes the stepwise mechanism proposed in the literature as the major pathway for the DMB cyclization reaction. This work provides important new insights into the origin of the 3′,5′‐dimethoxy substitution effect for the DMB photodeprotection. It also helps to clarify the many different views presented in previous mechanistic studies of the DMB PRPGs. In addition to this, our fs‐TA results on the reference compound DMBnDP in CH₃CN provide the first direct observation (to the best of our knowledge) showing the predominance of a prompt (≈2 ps) heterolytic bond cleavage after photoexcitation of meta‐methoxybenzylic compounds. This provides insight into the long‐term controversies about the photoinitiated dissociation mode of related substituted benzylic compounds.     

A novel antioxidant isobenzofuranone derivative from fungus Cephalosporium sp.AL031

Bioassay-guided fractionation of metabolites from the fungus Cephalosporium sp.AL031 isolated from Sinarundinaria nitida led to the discovery of a new isobenzofuranone derivative, 4,6-dihydroxy-5-methoxy-7-methylphthalide (1), together with three known compounds: 4,5,6-trihydroxy-7-methyl-1,3-dihydroisobenzofuran (2), 4,6-dihydroxy-5-methoxy-7-methyl-1,3-dihydroisobenzofuran (3) and 4,5,6-trihydroxy-7-methylphthalide (4). The structure of the new compound 1 was determined based on MS, 1D and 2D NMR spectral data. Compounds 1-4 showed potent antioxidant activity with EC?? values of 10, 7, 22 and 5 μM by 1,1-diphenyl-2-picryhydrazyl (DPPH) radical-scavenging assay.